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Aggregation of stereoregular poly(methyl methacrylates)
Advances in Colloid and Inter/ace Science, 27 (1987) 81-150
81
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
AGGREGATION J. S P E V A C E K
OF S T E R E O R E G U L A R
POLY(METHYL
METHACRYLATES)
a n d B. S C H N E I D E R
Institute of M a c r o m o l e c u ~ r Chemistry, Czechos]ovak A c a d e m y 162 06 P r a g u e 6, C Z E C H O S L O V A K I A
of Sciences,
CONTENTS
I.
ABSTRACT
II.
INTNOIXJG~ION ................................ .......................
...........................................................
82
III.
C2-1ARAC'rI~IZATION OF S
83
~
~
A. Configurational structure
(stereoregularity)
B. Confornmtional structure of ~
IV.
V.
............................. of I ~
............
83
................................
85
C. Dynamic properties of stereoregular PMMA ........................
87
METHODS USED IN STUDIES OF RMMA AGGREGATION (A SHORT SURVEY OF THEIR POSSIBILITIES) ............................................
89
A. Methods for dilute solution studies
9]
...........................
B. Methods for studies of concentrated solutions, gels and of the solid state .....................................................
]00
C. Methods of molecular spectroscopy (NMR spectroscopy, vibrational spectroscopy) ...................................................
]04
FORMATION AND CHARACTER OF AGGREGATES OF PMMA ......................
]]0
A. Stoichiometry of ~
.............................
|] 0
B. Effect of degree of stereoregularity on the formation of aggregates (minimtRn length of aggregated sequences) ..................
stereocomplex
] ]3
C. Thermal stability and decomposition of aggregates
]]9
...............
D. Kinetics of aggregation and effects of thermal history E. Effect of solvent on the formation of aggregates VI.
LOCAL S
~
OF A C ~ T E D
.......... ]23
................
]26
SEQUENCES OF PMMA ....................
T30
A. C h a r a c t e r of the interactions of functional groups responsible for aggregation ................................................
VII.
!30
B. Conformmtional structure of the aggregates of stereoregular ...........................................................
]34
ORDERING AND MOBILITY OF CHAINS IN AGf~EGATES OF PMMA .............
]36
A. Effect of aggregation on segmental mobility of the chains
]36
B. Chain ordering VIII.
82
......
.................................................
]38
OF PMMA ..........................................
]4 ]
A. Interactions o f stereoreEular PMMA with MMA monomer o r with dimer model of PMMA ............................................
]4!
OTHER A ~ T E S
B. Replica polymerization of MMA ..................................
T42
C. Other systems
143
0001-8686/87/$24.50
..................................................
© Elsevier Science PublishersB.V.
82
IX.
CONCLUS IONS
X.
REFERENCES
I.
ABSTRACT
.......................................................
]4 3
........................................................
]4 6
I n t h i s r e v i e w , e x p e r i m e n t a l r e s u l t s o b t a i n e d i n s t u d i e s of a g g r e g a t i o n stereoregular evaluated.
of
(PMMA) a r e r e v i e w e d a n d c r i t i c a l l y
B e s i d e s a g g r e g a t i o n in s o l u t i o n , a t t e n t i o n is a l s o p a i d to t h e
corresponding aggregates
poly(methyl methacrylates)
ordered
structures
of s t e r e o r e g u l a r
in t h e solid s t a t e .
PMMA a r e d i s c u s s e d
T h r e e t y p e s of
in p a r a l l e l : 1) t h e
s t e r e o c o m p l e x of PMMA f o r m e d b y t h e m i x i n g of s o l u t i o n s of i s o t a c t i c {i) a n d s y n d i o t a c t i c (s) PMMA; 2) t h e s e l f - a g g r e g a t e s self-aggregates
of s-PMMA; a n d 3) t h e
of i-PMMA.
In the introductory
sections, information on the conformational structure
a n d d y n a m i c b e h a v i o r of s t e r e o r e g u l a r s t a t e is s u m m a r i z e d .
PMMA i n s o l u t i o n s a n d in t h e solid
I n P a r t IV, t h e p o s s i b i l i t i e s of v a r i o u s p h y s i c a l m e t h o d s
in o b t a i n i n g v a r i o u s t y p e s of i n f o r m a t i o n o n PMMA a g g r e g a t e s demonstrated.
PMMA a g g r e g a t e s
are cited.
T h e p r o b l e m s of t h e s t r u c t u r e following three parts.
of PMMA a g g r e g a t e s
t h e r m a l s t a b i l i t y of s t e r e o c o m p l e x a g g r e g a t e s in P a r t V.
a r e t h e s u b j e c t of t h e
I n f o r m a t i o n c o n c e r n i n g t h e s t o i c h i o m e t r y of t h e PMMA
s t e r e o c o m p l e x a n d t h e e f f e c t s of s t e r e o r e g u l a r i t y
discussed
are
With e a c h m e t h o d , t h e m a i n r e s u l t s o b t a i n e d i n s t u d i e s of
on the formation a n d
a n d s-PMMA s e l f - a g g r e g a t e s
is
F o r t h e s e s y s t e m s in v a r i o u s s o l v e n t s , t h e v a l u e s of
t h e m i n i m u m l e n g t h of s - s e q u e n c e s
necessary
for aggregation are given.
A t t e n t i o n i s a l s o p a i d to t h e t i m e - c o u r s e of a g g r e g a t i o n a n d to i t s v a r i o u s stages.
I n P a r t VI, b a s e d o n t h e r e s u l t s of NMR a n d v i b r a t i o n a l
s p e c t r o s c o p y , it i s s h o w n t h a t a g g r e g a t i o n b y i n t e r a c t i o n s of e s t e r g r o u p s . PMMA a g g r e g a t e s stereoregular
of s t e r e o r e g u l a r
PMMA i s c a u s e d
The backbone conformational structure
sequences assume an approximately tt structure.
t h e e f f e c t s of a g g r e g a t i o n o n t h e m o b i l i t y a n d m u t u a l o r d e r i n g in a g g r e g a t e s
are described.
double-helical structures are discussed.
in
i s a l s o d i s c u s s e d i n t h i s c h a p t e r ; it i s s h o w n t h a t t h e I n P a r t VII, of t h e c h a i n s
Experimental results indicating that
are formed in a g g r e g a t i o n
of s t e r e o r e g u l a r
PMMA
I n f o r m a t i o n o n s o m e o t h e r s y s t e m s d i r e c t l y r e l a t e d to t h e
a g g r e g a t i o n of s t e r e o r e g u l a r
PMMA ( i n c l u d i n g t h e " r e p l i c a p o l y m e r i z a t i o n " of
m e t h y l m e t h a c r y l a t e ) is s u m m a r i z e d i n P a r t VIII.
II.
INTRODUCTION I n 1961, W a t a n a b e e t al. ( r e f . 1) r e p o r t e d
t h a t i n s o m e s o l v e n t s , m i x i n g of
t h e s o l u t i o n s of s y n d i o t a c t i c (s) PMMA a n d i s o t a c t i c (i) PMMA l e a d s to t h e f o r m a t i o n of a g g r e g a t e s ,
connected with pronounced
c h a n g e s of t h e
83 rheological properties
of t h e m i x t u r e .
c a l l e d " s t e r e o c o m p l e x PMMA". aggregation
solvent.
Further
and the properties
with the stereoregularity
The aggregates
thus formed were
r e s u l t s i n d i c a t e d t h a t t h e d e g r e e of
of t h e a g g r e g a t e s
of t h e i n t e r a c t i n g
are critically connected
p o l y m e r s a n d with the kind of
O p i n i o n s o n t h e n a t u r e of t h e i n t e r a c t i o n s l e a d i n g to s t e r e o c o m p l e x
formation have undergone
c o n s i d e r a b l e c h a n g e s in t h e c o u r s e of time.
N e v e r t h e l e s s , s i n c e t h e v e r y f i r s t p u b l i c a t i o n s , it h a s b e e n q u i t e c l e a r t h a t the aggregation
is c a u s e d b y w e a k i n t e r a c t i o n s , w i t h t h e i r r e s u l t s
by cooperative effects.
geometrical and dynamical structure of p a p e r s .
enhanced
T h e c o n d i t i o n s of s t e r e o c o m p l e x f o r m a t i o n a n d i t s h a v e b e e n t h e s u b j e c t of a g r e a t n u m b e r
I n t h e c o u r s e s of t h e s e s t u d i e s , it w a s a l s o f o u n d t h a t s-PMMA
a n d i-PMMA a l o n e c a n f o r m a g g r e g a t e s
i n s o m e s o l v e n t s ( r e f . 2,3).
it w a s r e c o g n i z e d t h a t i n t h e a g g r e g a t e s chains form helical structures helical structures
Gradually,
of s t e r e o r e g u l a r
PMMA, t h e PMMA
which are in some r e s p e c t s
a n a l o g o u s to t h e
of b i o l o g i c a l p o l y m e r s .
B e c a u s e of t h i s a n a l o g y a n d the
circumstance that stereocomplex formation strongly affects the properties PMMA m e m b r a n e s ( r e f . 4), s t u d i e s of t h e p r o p e r t i e s streoregular
PMMA a g g r e g a t e s
still a t t r a c t
In the s t u d i e s of s t e r e o r e g u l a r
and structure
considerable attention.
PMMA a g g r e g a t e s ,
various physical and physico-chemical methods.
u s e h a s b e e n m a d e of
I n t h i s r e v i e w , we h a v e
m a d e a n a t t e m p t to d i s c u s s all t h e m o r e i m p o r t a n t f i n d i n g s i r r e s p e c t i v e the method by which they were obtained.
of
of
of
Nevertheless, the conclusions are
certainly strongly affected by the circumstance that our own speciality is NMR a n d v i b r a t i o n a l s p e c t r o s c o p y .
III.
CHARACTERIZATION OF STEREOREGULAR
Of the structural parameters affecting P M M A
PMMA aggregation, the most
important factors are the configurational and conformational structure of PMMA
and the mobility of the various P M M A
functional groups; therefore, in
this part, the most important results of the studies of these parameters and the conventions used in their description will be summarized.
A. C o n f i ~ u r a t i o n a l s t r u c t u r e
(stereoregularity)
of PMMA
T h e d i f f e r e n c e s in t h e c o n f i g u r a t i o n a l s t r u c t u r e
o f PMMA a r e t h e r e s u l t o f
t h e c i r c u m s t a n c e t h a t C~ c a r b o n s o f t h e PMMA m o n o m e r u n i t s f o r m pseudoassymmetric centers.
A l t h o u g h t h e Ca c a r b o n i s n o t o p t i c a l l y a c t i v e ,
t h e d a n d 1 c o n f i g u r a t i o n of t h e Ca a t o m s c a n b e d i f f e r e n t i a t e d of the chain.
by inspection
A d i a d c o n t a i n i n g two C~ c a r b o n s of e q u a l c o n f i g u r a t i o n ( d d o r
U) i s d e s c r i b e d a s a n i s o t a c t i c d i a d ( s o m e t i m e s a l s o a m e s o [m] d i a d ) . d i a d f o r m e d b y two Ca c a r b o n s of u n e q u a l c o n f i g u r a t i o n (dl o r Id) is d e s c r i b e d a s a s y n d i o t a c t i c diad (sometimes also as a racemic [r] diad).
The
84 I 3 Ca
--
CH 2
I C
=
0
I
0
\ CH 3
B y configurational structure of P M M A , diads in the polymer. a linear b a c k b o n e chain.
T h e purely i - P M M A
we mean
the distribution of m a n d
consists of m diads only a n d with
structure, all ester g r o u p s are situated on one side of the
T h e purely s - P M M A
consists of r diads only; with a linear b a c k b o n e
structure, the ester g r o u p s alternate on both sides of the chain. configurational determination
r
structure of P M M A
can be most simply described
of the content of m a n d r diads.
The b y the
This result alone does not
yield a n y information on the distribution of m a n d r diads in longer sequences
which
determine
the content of i- a n d s-sequences
strongly affects the aggregation
information on the m e c h a n i s m
the sequence parameter
unit is independent
chain, then the g r o w t h is determined length distribution is determined
Pm(PrZl-Pm)
In order to
of the g r o w t h of the polymer chain is needed.
If the addition of a n y m o n o m e r the polymer
of P M M A .
of various length, some
of the configuration of b y Bernoulli statistics a n d
b y a single probability
which is defined b y the content of m a n d r diads
( r e f . 5). A l r e a d y in 1H NMR s p e c t r a m e a s u r e d a t 60 MHz, t h e c o n t e n t o f ram, m r a n d rr triads
( o f t e n d e s i g n a t e d a s I,H a n d S, r e s p e c t i v e l y , a n d g i v e n i n %) c a n
be d e t e r m i n e d f r o m t h e r e l a t i v e i n t e n s i t i e s of t h e =-CH 3 b a n d c o m p o n e n t s (ref. 5).
D e t e r m i n a t i o n s of t h e c o n t e n t of I,H,S t r i a d s h a v e s h o w n t h a t o n l y
PMMA s a m p l e s p r e p a r e d
by radical polymerization exhibit sequence
populations corresponding samples prepared
to B e r n o u l l i s t a t i s t i c s .
I n o t h e r c a s e s (PMMA
b y a n i o n i c p o l y m e r i z a t i o n ) , t h e c o n f i g u r a t i o n of t h e c h a i n
e n d h a s to b e c o n s i d e r e d i n t h e d e s c r i p t i o n of c h a i n g r o w t h . h a s to be d e s c r i b e d depends
by Markov statistics.
Such growth
In c a s e s w h e r e monomer a d d i t i o n
o n t h e c o n f i g u r a t i o n of o n l y t h e l a s t d i a d , f i r s t o r d e r M a r k o v
s t a t i s t i c s a r e s u f f i c i e n t f o r t h e d e s c r i p t i o n of c h a i n g r o w t h a n d t h e two necessary
probability parameters
I,H,S t r i a d s .
c a n b e d e t e r m i n e d f r o m t h e c o n t e n t of t h e
By m e a n s of 1H a n d 13C NMR s p e c t r a m e a s u r e d a t h i g h e r
magnetic fields, the content of e v e n longer sequences
can be determined
(e.g., tetrads a n d pentads from the analysis of the C H 2 a n d a - C H 3 b a n d s in IH N M R
spectra m e a s u r e d
of first order M a r k o v
higher order prepared
at 220 MHz) in order either to verify the validity
statistics or to determine the parameters
s t a t i s t i c s ( r e f . 5).
For most s t e r e o r e g u l a r
of s o m e
PMMA s a m p l e s
by conventional methods, first order Markov statistics are adequate
f o r t h e d e s c r i p t i o n of t h e c o n f i g u r a t i o n a l s t r u c t u r e
of PMMA.
85 T h e e q u a t i o n s r e l a t i n g t h e c o n t e n t s of I,H,S t r i a d s w i t h t h e two independent first order
probability parameters
d e t e r m i n i n g c h a i n g r o w t h a c c o r d i n g to
M a r k o v s t a t i s t i c s a n d p e r m i t t i n g t h e c a l c u l a t i o n of t h e c o n t e n t of
i- and s-sequences
of v a r i o u s l e n g t h a r e g i v e n in P a r t V-B.
B. C o n f o r m a t i o n a l s t r u c t u r e
of PMMA
I n PMMA, c o n f o r m a t i o n a l i s o m e r s c a n be g e n e r a t e d
by rotation about three
t y p e s of s i n g l e b o n d s : 1) t h e b o n d s b e t w e e n t h e m e t h y l e n e g r o u p a n d t h e quaternary
c a r b o n , CH2-C; 2) t h e b o n d s b e t w e e n t h e q u a t e r n a r y
and carbonyl
c a r b o n s , C-CO; a n d 31 t h e b o n d s b e t w e e n t h e c a r b o n y l c a r b o n a n d o x y g e n , CO-O.
R o t a t i o n a b o u t b o n d 1 (CH2-C) d e t e r m i n e s t h e c o n f o r m a t i o n a l s t r u c t u r e
of t h e c h a i n b a c k b o n e a n d r o t a t i o n a b o u t b o n d 2 (C-CO) d e t e r m i n e s t h e o r i e n t a t i o n of t h e e s t e r g r o u p s w i t h r e s p e c t
to t h e c h a i n .
Rotation about
b o n d 3 (CO-O) n e e d n o t b e c o n s i d e r e d i n s t u d i e s of t h e c o n f o r m a t i o n a l structure
of PMMA b e c a u s e in all s i m p l e m e t h y l e s t e r s a n a l y z e d so f a r , t h e
e s t e r g r o u p w a s f o u n d to h a v e a p l a n a r s t r u c t u r e g r o u p in cis o r i e n t a t i o n with r e s p e c t assumed that this structure
with the ester methyl
to t h e c a r b o n y l ; t h e r e f o r e , it m a y b e
of t h e e s t e r g r o u p i s p r e s e r v e d
CH
CH
131
- c
a l s o in PMMA.
1- i 3 cH
c
--
2
The structures described
generated
i n t e r m s of t r a n s
b y r o t a t i o n a b o u t CH2-C b o n d s a r e o f t e n (t) a n d g a u c h e (g) f o r m s e v e n if t h e y d e v i a t e
somewhat from the strictly staggered In this
chain with a planar arrangement a s tt, t h e s t r u c t u r e s by & 120"as tg.
of t h e b a c k b o n e c a r b o n a t o m s i s d e s i g n a t e d
w i t h o n e of t h e b o n d s 1 o r 2 t u r n e d
o u t of t h e p l a n e
By r o t a t i o n a b o u t b o n d 2 (C-CO), s i x d i f f e r e n t o r i e n t a t i o n s
of t h e e s t e r g r o u p w i t h r e s p e c t structure
structures.
"staggered a p p r o x i m a t i o n " , t h e c o n f o r m a t i o n a l f o r m of t h e PMMA
to t h e c h a i n c a n be g e n e r a t e d
(ref. 61.
The
w i t h t h e ~-CH 3 g r o u p c o p l a n a r w i t h t h e e s t e r g r o u p a n d o r i e n t e d
t o w a r d s t h e c a r b o n y l is d e s i g n a t e d a s " c i s (or s y n ) o r i e n t a t i o n of t h e e s t e r group with respect
to a-CII3"; t h e s t r u c t u r e
w i t h t h e a-CH 3 g r o u p c o p l a n a r
with t h e e s t e r g r o u p a n d o r i e n t e d a w a y from t h e c a r b o n y l is d e s i g n a t e d as "trans
(or a n t i ) o r i e n t a t i o n o f t h e e s t e r g r o u p w i t h r e s p e c t
Structures
to ~-CH3".
with -CH2-groups coplanar with the ester group can also appear
in PMMA, a s t h e s e c a n a g a i n b e e i t h e r of c i s ( s y n ) o r t r a n s
(anti) t y p e .
86
R
C
C C
0 syn R
0 anti
(cis R)
(trans
R R)
I. i-PMMA. T h e f i r s t c o n s i d e r a t i o n s a b o u t t h e c o n f o r m a t i o n a l s t r u c t u r e i-PMMA w e r e c o n n e c t e d w i t h t h e a n a l y s i s of X - r a y p a t t e r n s i-PMMA w h i c h w e r e o r i g i n a l l y i n t e r p r e t e d
of
of c r y s t a l l i n e
b a s e d o n t h e a s s u m p t i o n ( r e f . 7)
t h a t t h e c h a i n s of i-PMMA i n t h e c r y s t a l l i n e s t a t e f o r m a h e l i x w i t h f i v e m o n o m e r u n i t s p e r two t u r n s the conformational structure as tg.
([5/2] helix).
I n t e r m s of t h e s t a g g e r e d
forms,
of t h e c h a i n in s u c h a helix c a n be a p p r o x i m a t e d
A better agreement with the X-ray patterns
c o u l d be o b t a i n e d w i t h
t h e ( 5 / i ) h e l i x ( r e f . 8) b u t e v e n t h i s model d i d n o t a g r e e w i t h t h e t h e o r e t i c a l c a l c u l a t i o n s ( r e f . 9,10), a c c o r d i n g to w h i c h t h e e n e r g e t i c a l l y m o s t f a v o r e d f o r m of i-PMMA c h a i n s is e v e n m o r e e x t e n d e d t h a n t h e 5/1 helix. ordering 11).
of t h e 5 / 1 h e l i c e s i n t h e u n i t cell p r e s e n t e d
some difficulties (ref.
T h e r e f o r e , a t h i r d model w a s p r o p o s e d w h i c h d e s c r i b e d
patterns,
the X-ray
a s s u m i n g t h a t t h e u n i t cell of c r y s t a l l i n e i-PMMA i s f o r m e d b y two
double-stranded
helices d i s p l a c e d by c/2 along the c axis (fiber axis) with
r e s p e c t to o n e a n o t h e r
( r e f . 11,12).
Each double strand
helices with identical sense and direction. structure
Also, t h e
c o m p r i s e s two 10/1
I n t h e 10/1 helix, t h e c h a i n
c a n b e d e s i g n a t e d a s t t , w i t h t h e a n g l e s ~ a n d ~' d e v i a t i n g f r o m
the strictly staggered
t t f o r m b y 25" a n d I 0 " , r e s p e c t i v e l y .
This is in v e r y
g o o d a g r e e m e n t w i t h t h e t h e o r e t i c a l c a l c u l a t i o n s of V a c a t e l l o a n d F l o r y ( r e f . 13), a c c o r d i n g to w h i c h i n t h e e n e r g e t i c a l l y m o s t f a v o r e d f o r m of i-PMMA t h e a n g l e s ~ a n d ~' d e v i a t e f r o m t h e s t a g g e r e d
t t f o r m b y 23" a n d I I ' ,
g r o u p s a r e c o p l a n a r w i t h ~-CH 3 w i t h a l t e r n a t i n g
the ester
syn(cis) and anti(trane)
ester group orientation. M e a s u r e m e n t s of w i d e - a n g l e X - r a y s c a t t e r i n g of a m o r p h o u s solid i-PMMA s a m p l e s i n d i c a t e ( r e f . 14) t h a t a l s o h e r e t h e t t c o n f o r m a t i o n a l s t r u c t u r e most populated with alternating
syn- and anti-ester
groups.
is t h e
Besides the tt
form, a m o r p h o u s s a m p l e s also c o n t a i n tg a n d g t forms, in a g r e e m e n t with t h e o r e t i c a l p r e d i c t i o n s of S u n d a r a r a j a n al. ( r e f . 15).
a n d F l o r y ( r e f . 9) a n d o f G r i g o r e v a e t
M e a s u r e m e n t s of e n d - t o - e n d
indicate that tt chain structures s o l u t i o n (ref. 16).
d i s t a n c e s i n s o l u t i o n s of i-PMMA
are the most highly populated even in
87 2. s-PMMA. F o r a l o n g time, c r y s t a l l i n e s-PMMA c o u l d n o t be p r e p a r e d ; therefore,
the first information on the conformational structure
of s-PMMA
w a s o b t a i n e d f r o m t h e o r e t i c a l c a l c u l a t i o n s ( r e f . 9,10), f r o m small a n g l e n e u t r o n and X-ray scattering
( r e f . 17) a n d f r o m w i d e - a n g l e X - r a y s c a t t e r i n g
a m o r p h o u s solid s a m p l e s ( r e f . 18). energetically most favored structure
Theoretical calculations indicated that the of s-PMMA i s t h e s l i g h t l y d e f o r m e d t t
f o r m of t h e c h a i n , w i t h s y n o r i e n t a t i o n of e s t e r g r o u p s w i t h r e s p e c t ( r e f . 9,10,19).
of
Calculations have further
to =-CH 3
s h o w n t h a t in a m o r p h o u s s-PMMA
a n d in s-PMMA s o l u t i o n s , t h e p r e s e n c e of t g f o r m s of t h e c h a i n a n d s y n a n d a n t i o r i e n t a t i o n s of e s t e r g r o u p s w i t h r e s p e c t
to t h e c h a i n a r e a l s o to be
expected.
T h e r e s u l t s of w i d e - a n g l e s c a t t e r i n g
( r e f . 18), of n e u t r o n
scattering
( r e f . 17) a n d d i e l e c t r i c m e a s u r e m e n t s
(ref. 20) h a v e c o n f i r m e d t h e
r e s u l t s of t h e t h e o r e t i c a l c a l c u l a t i o n s .
A n a l y s i s of i n f r a r e d
(IR) s p e c t r a
has
s h o w n ( r e f . 21,22) t h a t s-PMMA i n s o l u t i o n c o n t a i n s a l a r g e p r o p o r t i o n of l o n g sequences
of t h e t t s t r u c t u r e .
T h e c o n t e n t of l o n g t t s e q u e n c e s
d i f f e r s in
v a r i o u s s o l v e n t s b u t it i s a l w a y s l a r g e r t h a n in solod a m o r p h o u s PMMA. f i n d i n g i s in a g r e e m e n t w i t h t h e r e s u l t s of i n t e r m e d i a t e - a n g l e scattering
This
X-ray
(ref. 23) w h i c h i n d i c a t e s a c o n s i d e r a b l e c o n t e n t of 9 - to
ll-membered
s e q u e n c e s of t t s t r u c t u r e s
of t h e c h a i n in s o l u t i o n s of s-PMMA.
P a r t l y c r y s t a l l i n e s-PMMA c o u l d be p r e p a r e d crystallization.
A n a l y s i s of X - r a y p a t t e r n s
by solvent-induced h a s i n d i c a t e d ( r e f . 24) t h a t i n
c r y s t a l l i n e s-PMMA t h e p o l y m e r c h a i n s f o r m h e l i c e s w i t h a l a r g e n u m b e r of monomer units per turn
( f o r m o r e d e t a i l , s e e P a r t VI-B).
From this s h o r t s u r v e y ,
it c a n be s e e n t h a t t h e c o n f o r m a t i o n a l s t r u c t u r e s
of t h e c h a i n i n t h e e n e r g e t i c a l l y m o s t f a v o r e d f o r m s of i - a n d s-PMMA d i f f e r v e r y little; in b o t h c a s e s i n t h e m o s t f a v o r e d f o r m , t h e c h a i n s t r u c t u r e be a p p r o x i m a t e d a s t t .
can
T h i s f i n d i n g is i n a g r e e m e n t w i t h t h e a n a l y s i s of t h e
conformational structures
of d i m e t h y l e s t e r s o f g l u t a r i c a c i d d e r i v a t i v e s , t h e
s i m p l e s t m o d e l s of PMMA d i a d s ( r e f . 25).
In these models, represented
by the
g e n e r a l f o r m u l a (RI,R2,R3)C1-CH2-C3(R4,R5,R6), t h e r e l a t i v e s t a b i l i t y of c o n f o r m e r s i s l a r g e l y d e t e r m i n e d b y t h e i n t e r a c t i o n s of s u b s t i t u e n t s p a r a l l e l C1-Ri a n d C3-Rj b o n d s ( p a r a l l e l 1-3 i n t e r a c t i o n s ) .
on
It was s h o w n t h a t
p a r a l l e l 1-3 i n t e r a c t i o n s of t w o e s t e r g r o u p s a r e a p p r o x i m a t e l y e q u a l to t h o s e of o n e m e t h y l a n d o n e e s t e r g r o u p . possible straight models. structures
with the longest
s e q u e n c e of s p 3 c a r b o n a t o m s a r e p r e f e r r e d
in t h e s e
B o t h t h e s e e f f e c t s l e a d to t h e s i m i l a r i t y of t h e c o n f o r m a t i o n a l of s - a n d i-PMMA c h a i n s .
C. D y n a m i c p r o p e r t i e s PMMA
Moreover, structures
of s t e r e o r e g u l a r
PMMA
contains several types of single bond rotations, which lead to
various internal motions of the polymer.
The barriers to rotation about the
88 v a r i o u s t y p e s of b o n d s a r e of c o n s i d e r a b l y d i f f e r i n g h e i g h t a n d t h e r e f o r e t h e m o l e c u l a r m o t i o n s of PMMA a r e c o m p l i c a t e d a n d e x h i b i t a s t r o n g dependence.
T h e d y n a m i c b e h a v i o r of PMMA c a n be d e s c r i b e d
f u n c t i o n s of t h e i n t e r n a l m o t i o n s G(T).
by correlation
U s u a l l y it is a s s u m e d t h a t t h e
c o r r e l a t i o n f u n c t i o n i s of e x p o n e n t i a l c h a r a c t e r
so t h a t the d y n a m i c b e h a v i o r
of t h e v a r i o u s f u n c t i o n a l g r o u p s of PMMA c a n be c h a r a c t e r i z e d c o r r e l a t i o n time Tc o r b y t h e c o r r e l a t i o n f r e q u e n c y The temperature
temperature
by the
vc, w h e r e 1 / r c = 2~v c.
d e p e n d e n c e o f t h e c o r r e l a t i o n f r e q u e n c i e s o f s o l i d PMMA
o b t a i n e d f r o m NMR r e l a x a t i o n p a r a m e t e r s , d i e l e c t r i c m e a s u r e m e n t s a n d m e c h a n i c a l m e a s u r e m e n t s i s s h o w n i n Fig. 1, w h i c h is b a s e d o n t h e d a t a o f McCall ( r e f . 26).
F r o m t h i s f i g u r e , it c a n b e s e e n t h a t t h e e s t e r m e t h y l
g r o u p i s t h e m o s t mobile, e x h i b i t i n g l a r g e c o r r e l a t i o n f r e q u e n c i e s
e v e n below
90"K; t h e a - m e t h y l g r o u p i s s o m e w h a t l e s s mobile, w i t h t h e r o t a t i o n a b o u t t h e C-CH 3 b o n d s t o p p i n g
(on t h e NMR time s c a l e , Vc<104-105Hz) a t t e m p e r a t u r e s
ca. 140"K; c h a i n b a c k b o n e m o t i o n s e x h i b i t t h e l o w e s t c o r r e l a t i o n f r e q u e n c i e s and thus the lowest mobility at a given temperature;
somewhat h i g h e r is the
m o b i l i t y of t h e e s t e r g r o u p a s a whole, w h i c h i s p r o b a b l y c o u p l e d w i t h t h e backbone motions.
T h e d y n a m i c b e h a v i o r of solid PMMA i s s t r o n g l y a f f e c t e d
by stereoregularity.
The glass transition
in) l i e s a t t h e t e m p e r a t u r e i-PMMA ( r s f . 27).
around
{where the b a c k b o n e motions set
115"C f o r s-PMMA a n d a r o u n d 45°C f o r
The data on the glass transition temperature
Tg d i f f e r
s o m e w h a t a c c o r d i n g to t h e m e t h o d b y w h i c h t h e y w e r e o b t a i n e d ; w i t h e a c h s i n g l e m e t h o d , h o w e v e r , T g of s-PMMA is a l w a y s h i g h e r b y a b o u t 70°C t h a n Tg of i-PMMA.
T h e m i n i m a i n NMR r e l a x a t i o n time m e a s u r e m e n t s , of l o s s
a n g l e s in mechanical m e a s u r e m e n t s a n d in dielectric m e a s u r e m e n t s corresponding temperatures 27).
to v a r i o u s f u n c t i o n a l g r o u p s f o r s-PMMA t h a n
of PMMA a l w a y s lie a t h i g h e r
the corresponding
m i n i m a f o r i-PMMA ( r e f .
This difference indicates that the resistance
to t h e r e o r i e n t a t i o n of all
g r o u p s i s h i g h e r i n s-PMMA t h a n i n i-PMMA. I n g e l s c o n t a i n i n g 60% w / w o r m o r e of t h e p o l y m e r , i n t e r n a l m o b i l i t y i s s i m i l a r to t h e m o b i l i t y in a solid p o l y m e r ( r e f . 28). backbone appears mobile.
At r o o m t e m p e r a t u r e ,
the
a s r i g i d o n t h e NMR s c a l e a n d o n l y t h e m e t h y l g r o u p s a r e
T h e m o t i o n s of t h e CH2 g r o u p s
representing
backbone motions only
s e t i n a t c o n c e n t r a t i o n s of 60-50% of t h e p o l y m e r a t room t e m p e r a t u r e . more dilute solutions where aggregation
In
d o e s n o t t a k e p l a c e , t h e m o t i o n of
t h e c h a i n is i s o t r o p i c (ref. 29), t h e m o t i o n of t h e =-CIt 3 g r o u p c a n b e described
b y t h e m o d e l of d o u b l e r e o r i e n t a t i o n w i t h two c o r r e l a t i o n t i m e s , Vg,
characterizing
r o t a t i o n a b o u t t h e b o n d C-CH 3 a n d To, c h a r a c t e r i z i n g
i s o t r o p i c m o t i o n of t h e r o t a t i o n a x i s ( r e f . 28,29). model i s n o t a d e q u a t e f o r c h a r a c t e r i z i n g
the
The double reorientation
t h e m o t i o n of t h e e s t e r CH3 g r o u p ;
in v e r y d i l u t e s o l u t i o n s , i t s m o t i o n c a n b e d e s c r i b e d
b y m e a n s of t h e log ×2
89
8
6 ~4 2 0
I.
-2 -4
'
I
I
I
1031T K q
F i g . 1. T e m p e r a t u r e dependence of the correlation frequency, ~c, f o r t h e m o t i o n s i n PMMA: m a i n c h a i n m o t i o n (o); m o t i o n o f t h e e s t e r g r o u p a s a w h o l e (e); r o t a t i o n o f t h e = - C H 3 g r o u p (z~); a n d r o t a t i o n o f t h e e s t e r CH 3 g r o u p (m). T h e d a t a b a s e d o n t h e r e s u l t s o f NMR s p e c t r o s c o p y , dielectric studies a n d d y n a m i c m e c h a n i c a l m e a s u r e m e n t s a r e t a k e n f r o m r e f . 26. distribution depends
of correlation
on the stereoregularity
temperatures, than
t i m e s ( r e f . 30).
the values
for s-PMMA.
correlation
frequencies
i-PMMA a n d
IV.
of the chains
of correlation
Therefore,
Even in solutions,
in chloroform,
of the a-CH 3 group
Vo=2.6xl08Hz , ~g=l.6xl08Hz
( r e f . 29,31).
frequencies
self-aggregates various
and
structure
f o r i-PMMA
are
uo=Sxl08Hz, vg:l.6xl09Hz
for
f o r s - P M M A ( r e f . 29).
AGGREGATION
of the stereocomplexes
(A S H O R T
o f PMMA a n d o f t h e
o f i-PMMA, s - P M M A o r a t - P M M A * a l o n e h a s b e e n f o l l o w e d b y
physical
methods.
references
of papers
included.
This section
basic principles monographs
At corresponding
higher
for example, at 27"C the
METHODS U S E D IN S T U D I E S O F P M M A S U R V E Y O F T H E I R POSSIBILITIES)
The formation
are
the mobility
They are exhaustively
in which the respective will n o t b e c o n c e r n e d
of the various
methods
( e . g . , i n r e f . 32) b u t
the aggregation
of stereoregular
methods.
In this
section,
in studies
of the aggregation
rather
summarized
in Table 1 and
method was applied with the explanation
which
can be found
with a review
of
of the information
on
some specific
o f PMMA w h i c h w e r e g a r d
of the
in a number
PMMA w h i c h c a n b e o b t a i n e d
we shall also include
are
by these results
as interesting
obtained and
* T h e t e r m a t - P M M A will b e u s e d t o d e s c r i b e PMMAs w i t h s u c h low stereoregularity that they cannot be designated as i- or s-PMMA. Besides samples with relatively high contents of both S- and I-triads, we use this designation also for conventional radical-polymerized PMMA, a l t h o u g h t h i s would also be described as s-PMMA of lower steroregularity, in view of the low c o n t e n t o f I - t r i a d s .
90 TABLE 1 S u r v e y of m e t h o d s u s e d in s t u d i e s of f o r m a t i o n a n d s t r u c t u r e
of PMMA
s t e r e o c o m p l e x a n d PMMA s e l f - a g g r e g a t i o n Method
PMMA s t e r e o c o m p l e x PMMA s e l f - a g g r e g a t i o n
(ref.)
(ref.)
turbidimetry
33-37
38b
light scattering
39-45,157,158
38b,42a,46a,47a,b158 b
sedimentation
40,48-51
osmometry
37,43
s p i n l a b e l m e t h o d s (EPR, fluorescence,luminescence)
56-58
52c,53c,54b,55 c
t h i n - l a y e r a n d GPC c h r o m a t o g r a p h y 4 3 , 4 9 , 5 9 flow b i r e f r i n g e n c e
42,60,61
42a,46a,62a,63 c
viscometry
34-37,39-44,51,52, 64-77
38b,42a,46a,47a, b, 52c,53c,54b,66c,70 a, 76b,78c,79c,80b,81b, c
m e a s u r e m e n t of gel m e l t i n g p o i n t and cloud point
1,67,82-85
53c
dielectric measurements and thermally stimulated depolarization c u r r e n t s
52,86,87
52 c
d y n a m i c o - m e c h a n i c a l m e a s u r e m e n t s 85,88-91,154 c a l o r i m e t r y a n d similar m e t h o d s
35-37,50,51,90-99, 154,156
x-ray diffraction
33,37,49,50,69,83, 90,94,95,97,100, 154
spectrroscopy
22b,23b,c,24b,38b, 95b$97b,100b,101b, 102 ° , 22 b
electron microscopy
NMR
91 c
29,65,69,103-108
2a,b 3a, b,c,3 b, 47a,~,c,54b,102 b, 1 0 9 a , b , l l 0 a , b , l l 1b
i n f r a r e d a n d Raman s p e c t r o s c o p y
21,22,29,41, 112-114,129
other
61,155
22b~lo1b~102b~111 b,
I15U,116o,129 o
ai-PMMA
bs-PMMA Cat-PMMA w h i c h , b y t h e i r c h a r a c t e r , do n o t f i t i n t o a n y of t h e p a r a g r a p h s following s e c t i o n s { P a r t s V - VII}.
of t h e
We did n o t r e f r a i n from d e m o n s t r a t i n g
e v e n some c o n t r a d i c t o r y r e s u l t s o b t a i n e d b y t h e same m e t h o d b y v a r i o u s authors.
The l a r g e n u m b e r of m e t h o d s a n d of p a p e r s d e v o t e d to s t u d i e s of
t h e s t e r e o c o m p l e x (73 r e f e r e n c e s ) a n d to s t u d i e s of t h e e i n g l e s t e r e o r e g u l a r
91 PMMA's, including the aggregation of at-PMMA
(34 references) prevent a more
detailed analysis of various papers. In this section, all methods summarized in Table i have been divided into three groups: 1) methods for dilute solution studies (turbidimetry, light scattering, osmometry, sedimentation, chromatography,
spin label methods, thin-layer and GPC
mixing calorimetry, flow birefringence, viscometry);
2)
methods for studies of concentrated solutions, gels and of the solid state (viscometry, measurements of the gel melting point, dielectric measurements and thermally stimulated depolarization currents, dynamic-mechanical measurements, D S C calorimetry, X-ray diffraction, electron microscopyl; 3) methods of molecular spectroscopy (NMR spectroscopy, IR and R a m a n spectroscopyl. In our classification, solutions with a concentration less than ~1% were considered as dilute; naturally, this limit should not be regarded dogmatically.
The methods of molecular spectroscopy have been separated
partly because of their specific character and partly because this is our o w n specialization.
A. Methods for dilute solution studies I. Turbidity. Liquori et al. (ref. 33) have already shown that the formation of the P M M A
stereocomplex in polar solvents (DMF, acetonitrile) is manifested
by enhanced turbidity.
In these media, the size of the stereocomplex
aggregate particles evidently reaches such values that the particles precipitate from solution (size ranges ~i00 n m to several micrometers).
The
dependences of the turbidity on the composition of the i/s-PMMA mixtures exhibit a maximum which is used to estimate the stoichiometry
of the
stereocomplex (ref. 33-35,37). Turbidity increases also with increasing concentration of the solution (ref. 33). During heating, an abrupt decrease of turbidity is observed in a certain temperature range (refs. 33,36), indicating deaggregation of stereocomplex particles. The turbidimetric methods have been applied in a more complex manner in studies of s - P M M A
seif-aggregation in butyl acetate (BAC) (ref. 38).
In this
case, the integral and differential turbidity ratio methods were applied for characterization
of the aggregating particles; the turbidities were measured
at three different wavelengths.
The solution of s - P M M A which was studied in
B A C was dissolved at high temperature where aggregates are not present in the system and aggregate formation was then followed by the measurement of the time dependence of turbidity at various temperatures for solutions of various concentration;
attention was also paid to the effect of the thermal
history of the solution. From the ratios of turbidities measured at various wavelengths, the size of the aggregating particles could be determined (i.e.,
92 t h e m e a n p a r t i c l e d i a m e t e r , t h e i r c o n c e n t r a t i o n c [g cm - 3 ] a n d / o r number N [cm-3])--all this for various aggregation
times.
2. C l a s s i c a l l i g h t s c a t t e r i n g . A n g u l a r l i g h t s c a t t e r i n g m e t h o d of d e t e c t i n g t h e p r e s e n c e of a g g r e g a t e s c a s e s w h e r e t h e f r a c t i o n of t h e a g g r e g a t e d
their
is a v e r y s e n s i t i v e
in t h e s y s t e m e v e n in t h o s e
m a c r o m o l e c u l e s is so s m a l l t h a t it
c a n n o t be d e t e c t e d b y o t h e r m e t h o d s like o s m o m e t r y , v i s c o m e t r y o r NMR spectroscopy
( r e f . 38).
of t h e a g g r e g a t i o n transparent.
T h e f o r m a t i o n of a g g r e g a t e s
the self-aggregates apparent
C o n t r a r y to t u r b i d i m e t r y ,
it p e r m i t s c h a r a c t e r i z a t i o n
p r o c e s s e v e n a t i t s b e g i n n i n g w h e n t h e s o l u t i o n is q u i t e of t h e PMMA s t e r e o c o m p l e x (or of
of i - o r s-PMMA) l e a d s to a m a r k e d i n c r e a s e in t h e
v a l u e s of molecular w e i g h t ( l ~ ) a p p .
t h e v a l u e s of ( l ~ ) a p p
which are dependent
F o r t h e PMMA s t e r e o c o m p l e x ,
on the composition (i/s) exhibit a
maximum; s i m i l a r l y , a s in t h e c a s e of t u r b i d i t y ,
t h i s i s u s e d f o r e s t i m a t e s of
t h e s t e r e o c o m p l e x s t o i c h i o m e t r y (ref. 39,42}.
D u r i n g h e a t i n g , a d e c r e a s e of
( l ~ } a p p is o b s e r v e d
w h i c h i s a c o n s e q u e n c e of t h e
at certain temperatures,
d e c o m p o s i t i o n of t h e s t e r e o c o m p l e x a g g r e g a t e s i n c r e a s e of ( ~ ) a p p
( r e f . 40,42}.
The absolute
a s c o m p a r e d to t h e a d d i t i v e v a l u e of t h e m i x t u r e d e p e n d s
a l s o o n t h e c o n c e n t r a t i o n o f t h e s o l u t i o n ( r e f . 43).
T h e r e s u l t s o f Katime e t
al. ( r e f . 45) i n d i c a t e t h a t e q u i l i b r i u m v a l u e s of ( H ~ ) a p p a n d of t h e r a d i u s of g y r a t i o n Rg f o r t h e s t e r e o c o m p l e x i n DMF a r e r e a c h e d o n l y a f t e r a b o u t 10 days. Increased
v a l u e s of ( l ~ } a p p w e r e a l s o o b s e r v e d
in DMF ( r e f . 42,46) a n d i n BAC ( r e f . 47). certain critical temperature,
w i t h s o l u t i o n s of i-PMMA
By h e a t i n g t h e s o l u t i o n a b o v e a
a p a r t of t h e i-PMMA a g g r e g a t e s
is i r r e v e r s i b l y
d e c o m p o s e d ( r e f . 46,47} a n d in t h e f o l l o w i n g t h e r m a l c y c l e s t h e s c a t t e r i n g d i a g r a m s do not differ.
A c c o r d i n g to K u s a k o v e t al. ( r e f . 46), t h e a g g r e g a t e s
of i-PMMA i n DMF d e c o m p o s e a t 50"C; h o w e v e r , in s t u d i e s of i-PMMA in BAC, it w a s f o u n d t h a t a m o l e c u l a r s o l u t i o n c a n be p r e p a r e d heating at temperatures
a b o v e 100-130"C ( r e f . 47).
By m e a n s of l i g h t s c a t t e r i n g , a g g r e g a t i o n methylethylketone
of s-PMMA w a s p r o v e d i n
(MEK}, 2 - e t h o x y e t h a n o l a n d BAC ( r e f . 38,47).
yields molecular solutions at temperatures temperature,
only by prolonged
aggregation
t a k e s place.
s-PMMA
a b o v e 60"C; b y c o o l i n g to a l o w e r
T h e time c o u r s e of a g g r e g a t i o n of
s-PMMA i n BAC a t 55"C f o l l o w e d b y m e a s u r e m e n t s of l i g h t s c a t t e r i n g i n Fig. 2, w h i c h c l e a r l y s h o w s t h e g r a d u a l g r o w t h of s c a t t e r e d w i t h time.
E v e n w i t h s-PMMA, a g g r e g a t i o n
characterized aggregation
turns
light intensity
c a n be a p p r o x i m a t e l y
b y t h e i n c r e a s e i n t h e v a l u e s o f (Nl~)app.
from solution.
is s h o w n
into macroscopic separation
A f t e r s o m e time,
( p r e c i p i t a t i o n } of t h e p o l y m e r
93
I
I
I
1:=10
×
40
1'0
0'5
1"5
2"0
2'5
S,n 2 (el2} * c-~
F i g . 2. D e p e n d e n c e o f t h e r a d i a t i o n e n v e l o p e s o f s e l f - a g g r e g a t i n g s - P M M A (S = 91.5%, H = 7.5%) i n BAC a t 55"C o n t i m e T {rain); c o n c . 5 x l 0 - 3 g c m - 3 ; C : 0.02 m i n - 1 ( r e f . 47).
3. Osmometry. From t h e concentration dependence of osmotic pressure, the n u m b e r average molecular weight, Mn, can be determined.
The intermolecular
interactions of macromolecules in stereocomplex formation are manifested by an increase of the Fin values, while the absolute effect depends on the ratio (i/s) in the mixture (ref. 37,43). Osmometry was also applied in a study of aggregation of s - P M M A in toluene (ref. 54). Also in this case, several-fold higher values of FIn were observed, indicating participation of intermolecular interactions in the aggregation process.
The decomposition of s - P M M A
aggregates with increasing temperature is manifested by a decrease of FIn values. Aggregation of a t - P M M A polymerization)
was studied
s-PMMA, also in this case exists
concerning
aaddition
to papers
This could probably
finding
the solvent
plays
claiming aggregation be explained
prepared by radical
(ref. 52-55). a major role.
measurements
no aggregation
i n r e f . 52, o r p o s s i b l y
4. Sedimentation.
PMMA
in a similar way
the osmometric
also exists one paper
defined
(conventional
Some discrepancy
of at-PMMA in toluene.
in this
system
stereoregularity
different
molecular
In
(ref. 53,54), there
at at-PMMA in toluene
by different
by very
Similarly as with
( r e f . 52).
which is not
weight.
Similarly as in the preceding methods, the increase of
the weight of the aggregated molecules in the stereocomplex of P M M A
makes
possible their detection by the method of sedimentation velocities (ref. 40,48,49). From the areas under the gradient curves, the weight fraction of
94 stereocomplex aggregates
can be e s t i m a t e d .
d i a g r a m s , Miyamoto a n d I n a g a k i d e m o n s t r a t e
On t h e b a s i s o f s e d i m e n t a t i o n ( r e f . 49} t h a t in a d d i t i o n to t h e
s t e r e o c o m p l e x , f r e e m o l e c u l e s of PMMA a r e p r e s e n t
i n m i x t u r e s of i / s - P M M A in
a c e t o n e w i t h t h e r a t i o i / s = 1/1 a n d 2 / 1 , t h e n u m b e r of f r e e m o l e c u l e s b e i n g c o n s i d e r a b l y h i g h e r in t h e l a t t e r c a s e .
Ultracentrifugation was also applied
f o r t h e p h a s e s e p a r a t i o n of t h e p r e c i p i t a t e d of t h e y i e l d i n d e p e n d e n c e
stereocomplex and determination
o n t h e r a t i o (i/s} {ref, 50} a n d o n t h e c o m p o s i t i o n
of t h e mixed s o l v e n t (ref. 51}.
5. S p i n l a b e l m e t h o d s (EPR, f l u o r e s c e n c e ~ l u m i n e s c e n c e } .
A common f e a t u r e
of t h e s e m e t h o d s i s t h e a t t a c h m e n t , b y c h e m i c a l r e a c t i o n , of a l a b e l d e t e c t a b l e by the respective
m e t h o d , to i - o r s-PMMA.
T h e a t t a c h m e n t of a n i t r o x i d e
r a d i c a l to i-PMMA h a s m a d e PMMA s t e r e o c o m p l e x f o r m a t i o n a m e n a b l e to EPR studies
( r e f . 56}.
F r o m t h e i n t e n s i t y of t h e b r o a d l i n e d u e to l i m i t e d m o b i l i t y
of t h e r a d i c a l in t h e s t e r e o c o m p l e x , s t u d i e d i n d e p e n d e n c e o n t h e r a t i o {i/s} and on temperature,
the authors
m a k e c o n c l u s i o n s a b o u t t h e s t o i c h i o m e t r y of
the steroecomplex and about its "melting". i - a n d s-PMMA m a c r o m o l e c u l e s c a r r y i n g
T h e i n t e r m o l e c u l a r i n t e r a c t i o n s of
l u m i n i s c e n c e l a b e l s in d i l u t e DMF
s o l u t i o n s a r e a l s o m a n i f e s t e d i n t h e m e t h o d of p o l a r i z e d l u m i n e s c e n c e d u e to reduced
m o b i l i t y {ref. 58).
The authors
of t h i s p a p e r c h a r a c t e r i z e
q u a n t i t a t i v e l y t h e i n t r a m o l e c u l a r m o b i l i t y of t h e s y n d i o t a c t i c c o m p o n e n t of t h e s t e r e o c o m p l e x in d e p e n d e n c e on the s t e r e o r e g u l a r i t y solvent.
By t h i s m e t h o d , t h e time d e p e n d e n c e
c o u l d a l s o b e followed.
of s-PMMA a n d o n t h e
of s t e r e o c o m p l e x f o r m a t i o n
Contact carbazole and anthracene
s - a n d i-PMMA f a v o r t h e e n e r g y
transfer
l a b e l s a t t a c h e d to
a n d m a k e p o s s i b l e s t u d i e s of
s t e r e o c o m p l e x formation in dioxane by the f l u o r e s c e n c e t e c h n i q u e
6. C h r o m a t r o g r a p h i c m e t h o d s . a n a l y s i s of t h e p r o d u c t s c o u l d be s e p a r a t e d
( r e f . 57}.
By m e a n s of t h i n l a y e r c h r o m a t o g r a p h y
i n t o two c o m p o n e n t s :
a n d i-PMMA, r e s p e c t i v e l y
{ref. 49,59).
a m i x t u r e w i t h i / s = 1/1 p l u s s -
From this finding, the authors
c o n c l u s i o n s a b o u t t h e c o m p o s i t i o n of t h e p r i m a r y s t e r e o c o m p l e x .
measured
some
c o n c e r n i n g t h e s t e r e o c h e m i c a l c o m p o s i t i o n of t h e p r o d u c t s .
r e s u l t s of GPC c h r o m a t o g r a p h y
make
H o w e v e r , it
s h o u l d b e s t a t e d t h a t t h e 60 MHz 1H NMR s p e c t r a of t h e p r o d u c t s a t 30"C w e r e n o t well r e s o l v e d ( s e e r e f . 59}, t h u s i n t r o d u c i n g uncertainty
and
b y NMR m e t h o d s , t h e m i x t u r e s w i t h i / s = 1/2 o r 2 / 1
The
h a v e s h o w n t h a t t h e p a r t i c l e s of t h e PMMA
s t e r e o c o m p l e x i n DMF a s a w h o l e a r e c o n s i d e r a b l y l a r g e r t h a n t h e coils of i o r s-PMMA a l o n e ( r e f . 43}.
7. Mixing c a l o r i m e t r y .
Mixing c a l o r i m e t r y w a s a p p l i e d to
s t e r e o c o m p l e x s t u d i e s i n two p a p e r s
( r e f . 93,99).
PMMA
F r o m m e a s u r e m e n t s of t h e
95 h e a t o f mixing of s o l u t i o n s of i - a n d s-PMMA, Biro~ e t al. ( r e f . 93) h a v e d e t e r m i n e d t h e h e a t of s t e r e o c o m p l e x f o r m a t i o n , aHf, a n d h a v e a l s o s t u d i e d i t s d e p e n d e n c e on t h e r a t i o i / s , o n t h e s o l v e n t a n d on t h e s t e r e o r e g u l a r i t y of the s-component.
The l a r g e s t v a l u e s (aHf} w e r e f o u n d in DMF (conc. 1%},
w h e r e f o r i / s = 1/1.5 to 1/2 a n d s-PMMA of h i g h s t e r e o r e g u l a r i t y (S = 94%; H = 6%), aHf = -15 J / g .
Similar v a l u e s of AHf w e r e a l s o f o u n d in CC14 (ref. 99}.
8. Flow b i r e f r i n g e n c e . M e a s u r e m e n t s of flow b i r e f r i n g e n c e h a v e s h o w n t h a t t h e v a l u e s of s e g m e n t a l a n i s o t r o p y of t h e PMMA s t e r e o a o m p l e x in t o l u e n e a r e n e g a t i v e a n d of h i g h a b s o l u t e v a l u e , i n d i c a t i n g a c o n s i d e r a b l e d e g r e e of o r d e r i n g of t h e s e s y s t e m s (similar to t h a t , f o r example, in m a c r o m o l e c u l e s of t h e biological origin} ( r e f . 42,60).
The d e p e n d e n c e of t h e s e g m e n t a l
a n i s o t r o p y o n t h e r a t i o i / s i n d i c a t e d t h a t maximum o r d e r of s t e r e o c o m p l e x a g g r e g a t e s is a t t a i n e d a t t h e r a t i o i / s = 1/1.
The h e a v i e s t s t e r e o c o m p l e x
p a r t i c l e s f o r m e d at i / s = 1/2 a r e t h u s n o t n e c e s s a r i l y t h e b e s t o r d e r e d o n e s ( r e f . 60).
The a u t h o r s f u r t h e r
d e m o n s t r a t e t h e e f f e c t of t h e r m a l h i s t o r y o f
t h e s a m p l e s w h i c h c a n lead to f u r t h e r i n c r e a s e o f t h e o r d e r i n g in t h i s s y s t e m . N e g a t i v e v a l u e s of a n i s o t r o p y of h i g h a b s o l u t e v a l u e i n d i c a t i n g t h e p r e s e n c e of o r g a n i z e d s t r u c t u r e s
w e r e o b s e r v e d a l s o with t o l u e n e s o l u t i o n s of
i-PMMA (ref. 42,46,62} a n d w i t h PMMA of " s t e r e o b l o c k " s t r u c t u r e
(I = 46%; H =
28%; S = 33%); in t h e l a t t e r c a s e , t h e y a r e a s c r i b e d to i n t e r a c t i o n s of i - a n d s - s e q u e n c e s of t h e same molecule ( r e f . 62).
Negative and t e m p e r a t u r e
d e p e n d e n t v a l u e s of o p t i c a l a n i s o t r o p y w e r e a l s o o b s e r v e d w i t h n e t w o r k s of at-PMMA s w o l l e n in CC14. ( r e f . 63). 9. V i s c o m e t r y . As s e e n f r o m Table 1, v i s c o m e t r y is t h e most f r e q u e n t l y 1 5 1 5 u s e d m e t h o d in s t u d i e s of t h e s t e r e o c o m p l e x of PMMA. This c i r c u m s t a n c e ,
t o g e t h e r w i t h t h e c o m p l i c a t e d n a t u r e a n d c o m p l e x i t y of s t e r e o c o m p l e x a g g r e g a t e f o r m a t i o n , h a s led to a n u m b e r of e v i d e n t l y o r a p p a r e n t l y controversial findings.
S t e r e o c o m p l e x f o r m a t i o n is u s u a l l y a s s u m e d to b e
i n d i c a t e d b y t h e n o n a d d i t i v e d e p e n d e n c e of t h e r e d u c e d s p e c i f i c v i s c o s i t y ~ s p / C o n t h e r a t i o i / s in t h e m i x t u r e .
I n DMF (in w h i c h s t e r e o c o m p l e x
f o r m a t i o n h a s b e e n most o f t e n s t u d i e d } , t h i s d e p e n d e n c e e x h i b i t s a minimum a n d t h e c o r r e s p o n d i n g r a t i o i / s is a s s u m e d to c o r r e s p o n d to t h e s t o i c h i o m e t r y o f t h e s t e r e o c o m p l e x (ref. 34-37,43,68,76} (Fig. 3).
The time
d e p e n d e n c e o f ~sp/C in DMF e x h i b i t s a n i n i t i a l d e c r e a s e ( r e f . 44), w h e r e a s i t s temperature d e p e n d e n c e (ref. 40,64).
exhibits an increase in a certain temperature range
Also, in the d e p e n d e n c e of intrinsic viscosity [7] (although the
determination of this quantity is s o m e w h a t problematic - see further text) on the ratio i/s in DMF, a m i n i m u m w a s observed
(ref. 39,44). These results
indicate that in this m e d i u m the h y d r o d y n a m i c
volume of the stereocomplex
96
o
2
0
~
\----22222
I
0
I
I
I
0.2 0.4 0.{5Ys __0.8 1.0
F i g . 3. D e p e n d e n c e o f t h e r e d u c e d v i s c o s i t y , l s p / C v s . s - P M M A c o n t e n t Y s f o r m i x t u r e s o f i-PMMA (I : 94%; H = 3%) a n d s - P M M A (S : 80%; H : 7%} i n c h l o r o f o r m (x), b e n z e n e (o) a n d DMF (o) ( r e f . 35).
aggregates is smaller than would correspond to a mixture on non-interacting i- and s-PMMA molecules; i.e., compact particles are observed. A minimum in the dependence of reduced specific viscosity on the ratio i/s, besides in DMF, was also observed in acetonitrile, acetone, dimethylsufoxide (DMSO), methyl isobutyrate, tetrahydrofurane (THF), MMA, BAC and ethyl acetate (EtAc) (ref. 35,71). However, it has to be remembered that ,}sp/C also depends on further factors, especially on the time from the mixing of the solutions of i- and s-PMMA and on their concentration.
With increasing time and especially at
higher concentration (above 0.5%), the values of Wsp/C increase even in DMF, reaching finally higher than additive values (i.e., exhibiting a maximum in the dependence on the ratio i/s) (ref. 35,43,76). T h i s behavior is explained by a gradual formation of a three-dimensional network, with small regions of associated and
segments
concentration
playing may then
( r e f . 65,71) f o r m i x t u r e s Greater studies
a role of crosslink
of i- and
discrepancies
of stereocomplex
formation
In a number
dependence
o f ,~sp/C o n i / s i s c i t e d
weaker
of papers
of a three-dimensional
"tendency
contradiction
towards
of the result
Differences
in time
o f m i n i m a ( r e f . 35) o r m a x i m a
s-PMMA in acetone.
are found
or toluene.
formation
points.
explain the findings
in the results in nonpolar
obtained
aromatic
by viscometric
solvents
like benzene
(ref. 35,52,65,66,69), a maximum in the ( F i g . 3) a n d
network
formed
complex formation" documenting
this is connected
with the
as a consequence
of a
of these
the existence
solvents
( r e f . 35).
In
o f a m a x i m u m Wsp/C i n
97 t o l u e n e , b o t h f r o m m e a s u r e m e n t s of e q u i l i b r i u m v a l u e s ( a b o u t 1 m o n t h a f t e r m i x i n g of i - a n d s-PMMA s o l u t i o n s } ( r e f . 65,69} o r f r o m m e a s u r e m e n t s p e r f o r m e d 10 rain. a f t e r m i x i n g ( r e f . 35}, o t h e r p a p e r s i n d i c a t e t h a t i n t h i s solvent at concentrations
below 1%, t h e v a l u e s of Wsp/C i n d e p e n d e n c e
on
time, a f t e r s o m e i n i t i a l d e c r e a s e , a t t a i n e q u i l i b r i u m v a l u e s ( r e f . 67,74), sJLmilarly a s in DMF ( r e f . 44).
A s t e e p i n c r e a s e of Wsp/C w i t h t i m e i s h e r e
c i t e d o n l y f o r c o n c e n t r a t i o n s a b o v e 1%. observed
R e h a g e a n d W a g n e r ( r e f . 76) h a v e
a m i n i m u m e v e n i n t o l u e n e , if t h e m e a s u r e m e n t s w e r e m a d e
immediately a f t e r mixing of the solutions; a f t e r s e v e r a l h o u r s , t h e minimum p a s s e s o v e r into a maximum. indicate that the aggregates
T h e r e s u l t s of t h e l a t t e r p a p e r s
t h u s s e e m to
of t h e PMMA s t e r e o c o m l e x in DMF a n d in t o l u e n e
a r e of t h e s a m e t y p e . T h e v i s c o s i t i e s of m i x t u r e s o f s o l u t i o n s of i - a n d s-PMMA d e p e n d a l s o o n t h e m o l e c u l a r w e i g h t of t h e s t e r e o r e g u l a r their stereoregularity. the additive character
c o m p o n e n t s {ref. 37,65,71} a n d o n
Low s t e r e o r e g u l a r i t y of r e d u c e d
was probably the reason why
specific viscosity was observed
for
m~ixtures of i - a n d at-PMMA i n b e n z e n e o r i n t o l u e n e ( r e f . 70,71}. behavior indicating that interaction between highly stereoregular PMMA d o e s n o t t a k e p l a c e c a n be r e g a r d e d 3) ( r e f . 35,65 69}.
Additive f o r m s of
a s p r o v e d o n l y in c h l o r o f o r m (Fig.
L o h m e y e r e t al. ( r e f . 36} h a v e followed v i s c o m e t r i c a l l y t h e
i n t e r a c t i o n b e t w e e n i-PMMA a n d p a r t l y h y d r o l y z e d c o s y n d i o t a c t i c c o p o l y m e r MMA/MAA.
s-PMMA, w h i c h i s r e a l l y a
E v e n f o r r e l a t i v e l y h i g h d e g r e e s of
h y d r o l y s i s , w h e r e t h e m e a n l e n g t h o f MMA s e q u e n c e s i s r e l a t i v e l y s h o r t , in DMF a d e c r e a s e of v i s c o s i t y below t h e a d d i t i v e v a l u e w a s o b s e r v e d , characteristic
f o r t h e f o r m a t i o n o f t h e PMMA s t e r e o c o m p l e x .
which is
M e k e n i t s k a y a et
al. ( r e f . 74} s t a t e t h a t t h e r e s u l t s of v i s c o m e t r i c s t u d i e s c a n b e a f f e c t e d b y t h e c i r c u m s t a n c e t h a t two p r o c e s s e s
p r o c e e d in parallel:
1) f o r m a t i o n of s t
e r e o c o m p l e x p a r t i c l e s ; a n d 2) a g g r e g a t i o n o f t h e s e p a r t i c l e s . have observed
The authors
t h e a g g r e g a t i o n o f s t e r e o c o m p l e x p a r t i c l e s i n DMF, b u t n o t i n
toluene. I n a n u m b e r o f p a p e r s , t h e v a l u e s of i n t r i n s i c v i s c o s i t y w e r e o b t a i n e d b y e x t r a p o l a t i o n o f t h e v a l u e s of ~ s p / C to z e r o c o n c e n t r a t i o n a n d t h e i r d e p e n d e n c e o n t h e r a t i o i / s ( r e f . 39,44,70,71} o r o n t e m p e r a t u r e w a s followed.
( r e f . 42,71,74}
H o w e v e r , B e l n i k e v i t c h e t al. ( r e f . 44) call a t t e n t i o n to t h e
c i r c u m s t a n c e t h a t i n t r i n s i c v i s c o s i t i e s d e t e r m i n e d in t h i s w a y a r e n o t s u i t a b l e fox" c h a r a c t e r i z i n g aggregates.
unambiguously the hydrodynamic
b e h a v i o r of s t e r e o c o m p l e x
T h i s is b e c a u s e t h e t i m e d e p e n d e n c i e s of ~ s p / C e x h i b i t a
d i f f e r e n t c o u r s e f o r v a r i o u s c o n c e n t r a t i o n s , w h i c h is, i n t e r alla, m a n i f e s t e d a l s o so t h a t t h e v a l u e s of [~] d e t e r m i n e d b y d i l u t i o n of t h e b a s i c s o l u t i o n , w h i c h h a s b e e n s t a b i l i z e d f o r a c e r t a i n time, d e p e n d o n t h e c o n c e n t r a t i o n o f t h i s s o l u t i o n ( r e f . 40,44).
As s e e n f r o m Fig. 4, t h e v a l u e s of [W] i n
98
I
I
i
a 6o-
3o
I
I
}
b60
C
130
__
-
IOO
I
J
j
2
4
6
Cm × [0 3 (g cm-3)
F i g . 4. D e p e n d e n c e o f t h e i n t r i n s i c v i s c o s i t y o f m i x t u r e s o f s o l u t i o n s o f i-PMMA (I : 72%; H : 17%1 a n d s - P M M A (S : 91.5%; H = 7.5%) o n t h e t o t a l initial concentration c m a t m i x i n g i n DMF (a), d i o x a n e ( b ) , a n d c h l o r o b e n z e n e (c); . . . . . , a d d i t i v e v a l u e ( r e f . 44). dependence and
on the total concentration
below the additive
not mean that
aggregation
Viscometric results (ref. 42,46,47,76) and intrinsic
value.
viscosity
with measurement
does not take
also indicate
with increasing
was described
observed
at temperatures
and its measurements observed,
indicating
sufficiently indicating reduced
long time (several a slow generation
does
( r e f . 461 o f
i n DMF i s c i t e d .
an irreversible their
In agreement
decomposition
of a part
heating
a certain
above
(ref. 46,47).
60"C.
( F i g . 5). hours)
of large
behavior
have
After cooling of the solution
at 25"0, an increase association
specific viscosity
decrease
no anomalies in viscometric above
thus
o f i-PMMA i n s o l u t i o n
( r e f . 42) a n d
i n DMF o r BAC a f t e r
With s-PMMA in toluene,
lie b o t h a b o v e
value
place.
temperature
of light scattering,
critical temperature
with the additive
self-aggregation
both an increase
o f t h e i-PMMA a g g r e g a t e s
a t m i x i n g (c m) c a n t h e n
Agreement
of the values The values
increase
of ~sp/C with time is
~sp/C measured
with decreasing
formations
with time was observed
( r e f . 54).
been
f r o m 60"C
after
concentration,
A growth
also with solutions
of of
a
99
I
r
f
10
~8
2
~00
200
300 time,rain
Fig. 5. D e p e n d e n c e o f ~splc - [7] v s . time ([7] : 0.52, d e t e r m i n e d a t 60"C) f o r s a m p l e s-PMMA (S = 89.5%; H = 8.5%) in t o l u e n e a t 25"C: c : 4.47 (o); 2.79 ( , ) ; 2.03 (/'); 1.4 (-); 0.86 ($) gL -1 ( r e f . 54). s-PMMA in BAC.
An a n o m a l o u s c o n c e n t r a t i o n d e p e n d e n c e of Wsp/C a n d g r o w t h
o f v i s c o s i t y w i t h time, i n d i c a t i n g t h e f o r m a t i o n of a n e t w o r k s t r u c t u r e , was o b s e r v e d a l s o w i t h s-PMMA in t o l u e n e a n d o - x y l e n e ( r e f . 76).
Katime e t al.
( r e f . 80,81) h a v e d e t e c t e d a n o m a l i e s in t h e t e m p e r a t u r e d e p e n d e n c e o f [7] w i t h s-PMlVlA in d i f f e r e n t s o l v e n t s , w h i c h t h e y i n t e r p r e t b y a c o n f o r m a t i o n a l t r a n s i t i o n b u t a c o n n e c t i o n w i t h a s s o c i a t i o n is a d m i t t e d .
However, similarly
a s w i t h t h e s t e r e o c o m p l e x , a l s o in t h e s e p a p e r s t h e d e t e r m i n a t i o n of i n t r i n s i c v i s c o s i t y r a i s e s some d o u b t s (see r e f . 54). Contradictory data have been published concerning the aggregation b e h a v i o r of at-PMMA.
B o r c h a r d e t al. ( r e f . 52,66) h a v e o b s e r v e d a maximum
in t h e t e m p e r a t u r e d e p e n d e n c e of ~/sp/C, a s well a s a n a n o m a l o u s c o n c e n t r a t i o n d e p e n d e n c e w i t h s o l u t i o n s of at-PMMA in t o l u e n e ; t h i s t h e y e x p l a i n b y i n t r a m o l e c u l a r a s s o c i a t i o n of s h o r t i - a n d s - s e q u e n c e s i n t e r a c t i o n s of stereocomplex type).
(i.e.~ b y
C o n t r a r y to t h i s , t h e f i n d i n g t h a t a l s o
w i t h at-PMMA in t o l u e n e t h e v a l u e s of ~sp/C a r e t i m e - i n d e p e n d e n t a n d e x h i b i t the conventional linear concentration dependence argues against the existence of a g g r e g a t e s in t h e s e s y s t e m s ( r e f . 54,76).
In t h e s e cases, an important
f a c t o r p r o b a b l y is t h e m o l e c u l a r w e i g h t o f at-PMMA.
The r e l a t i v e l y h i g h
v a l u e s of t h e H u g g i n s c o n s t a n t (k H ~ 1) i n d i c a t e t h e e x i s t e n c e of some i n t e r m o l e c u l a r i n t e r a c t i o n s in s o l u t i o n s o f at-PMMA in a c e t o n i t r i l e , c h l o r o b u t a n e a n d p - x y l e n e ( r e f . 53,54,78,79).
100 B. M e t h o d s for studies of concentrated solutions, gels a n d of the solid state. i. Rheology. It follows already from the p a r a g r a p h concerning the viscometric behavior of dilute solutions that with increasing concentration and time, the interactions between s- a n d i - P M M A in D M F
lead to the
formation of a gel. Mixing of concentrated solutions of i- and s - P M M A several per cent) leads to almost instantaneous gel formation.
(conc.
F r o m the
macroscopic point of view, these gels exhibit a sharp melting point considerably d e p e n d e n t on the stereoregularity of s - P M M A
(ref. I).
Similarly,
a d e p e n d e n c e on the stereoregularity of i - P M M A could be expected but this has not been studied.
It w a s found that gel formation does not take place if
the molecular weight of i- or s - P M M A
decreases below a certain limit (N~ <
i000) (ref. 82,83). The d e p e n d e n c e of the gel melting temperature on the total concentration (ref. 1,85) and on solvent (ref. 67) w a s studied.
Gel
formation w a s observed also for mixtures of solutions of i- a n d a t - P M M A acetone (ref. 84). Methodically similar to the above-mentioned also are the studies of aggregation of a t - P M M A
in
investigations
in CCI 4 or in p-xylene from
m e a s u r e m e n t s of cloud-point curves (ref. 52). Viscometry w a s applied to studies of mixtures of concentrated solutions (conc. 2 - 10%) of i- a n d a t - P M M A
in benzene, D M F
a n d toluene (ref. 70,75).
In d e p e n d e n c e on the ratio i/at-PMMA, the viscosity exhibits an e x t r e m u m a n d approaches additive behavior with increasing temperature, with the nature of the solvent playing some role. F r o m the temperature d e p e n d e n c e of viscosity, 7, using the relation w - A exp[(AH ;~ - TaS~)/RT], the activation enthalpy AH ;~ a n d activation entropy aS ;~ of the viscous flow has been determined.
T h e relatively high values of these quantities found in D M F
(AH ;~
= 31 kcal/mol; AS~ = 70 cal/mol) indicate that the flow is accompanied b y decomposition of strong intermolecular b o n d s a n d b y a considerable disordering of supermolecular structures (ref. 75). T h e presence of rigid organized structures is indicated b y viscometry also in 10% solutions of i - P M M A alone in benzene (ref. 70). T h e viscoelastic behavior of gels of the P M M A
stereocomplex in o-xylene
(conc. 5-12%) w a s studied b y dynamicomechanical techniques (i.e., b y the m e a s u r e m e n t of the time d e p e n d e n c e s of the real a n d imaginary c o m p o n e n t s of t h e s h e a r m o d u l u s ( s t o r a g e m o d u l i G' a n d l o s s m o d u l i G") ( r e f . 88,89,91). A g r a d u a l l o w e r i n g of t h e t e m p e r a t u r e
to a v a l u e w h e r e g e l f o r m a t i o n t a k e s
p l a c e is m a n i f e s t e d b y a s t e e p i n c r e a s e of G' a n d G" ( t h e c h a n g e of G' in a narrow temperature
r a n g e a m o u n t s to 8 o r d e r s )
(Fig. 6).
Viscoelastic
m e a s u r e m e n t s i n d i c a t e t h e f o r m a t i o n of a n e t w o r k v e r y s i m i l a r to t h e g e l s of c h e m i c a l l y c r o s s l i n k e d p o l y m e r s a n d it i s a s s u m e d t h a t t h e c r o s s l i n k p o i n t s are represented
by v e r y small c r y s t a l l i n e r e g i o n s .
101 The t e m p e r a t u r e d e p e n d e n c e s of t h e l o s s t a n g e n t (tg6 = G"/G') of b l e n d s of i - a n d s-PMMA a n n e a l e d f o r 120 h r s at 140"C a r e a s y m m e t r i c a l a n d e x h i b i t
togS' tog
if,
G"534
0log ~.
0 -1
30
I
I
50
I
I
I
J
90 temperoture."C 70
Fig. 6. T e m p e r a t u r e d e p e n d e n c e of t h e s t o r a g e moduli G ' [ d y n cm -2] (o), of t h e l o s s moduli G" ( [ d y n cm -2] (o) a n d of t h e r a t i o G"/G' (Q) f o r m i x t u r e s o f c o n c e n t r a t e d s o l u t i o n s o f i-PMMA (I = 93%) a n d s-PMMA (S = 72%; H : 28%) in o - x y l e n e (mixing r a t i o r = 1.25) (ref. 88). a maximum s h i f t e d t o w a r d s h i g h e r t e m p e r a t u r e s a s c o m p a r e d to n o n a n n e a l e d samples; Feitsma etal.
( r e f . 90) c o n s i d e r t h i s a s i n d i c a t i o n of s t e r e o c o m p l e x
f o r m a t i o n in bulk.
2. D i e l e c t r i c m e a s u r e m e n t s a n d m e a s u r e m e n t s of t h e r m a l l y s t i m u l a t e d depolarization currents.
The monomer u n i t of PMMA h a s a p e r m a n e n t d i p o l e
moment ( p o l a r e s t e r g r o u p ) a n d t h e mean v a l u e of t h e d i p o l e moment of t h e whole m a c r o m o l e c u l e d e p e n d s on i t s c o n f i g u r a t i o n a n d c o n f o r m a t i o n ; in s t u d i e s of s o l u t i o n s o f s t e r e o r e g u l a r pMIV[A in t o l u e n e (conc. 1-5%), t h i s h a s made p o s s i b l e t h e a p p l i c a t i o n o f m e a s u r e m e n t s o f t h e t e m p e r a t u r e d e p e n d e n c e of b o t h c o m p o n e n t s (~',~") of t h e complex d i e l e c t r i c c o n s t a n t ( r e f . 52).
The
f o r m a t i o n a n d d e c o m p o s i t i o n o f t h e s t e r e o c o m p l e x in t h e t e m p e r a t u r e r a n g e 20 -
90"C is m a n i f e s t e d b y a c o n s i d e r a b l e time d e p e n d e n c e o f t h e m e a s u r e d
values and by t h e i r d e p e n d e n c e on the thermal h i s t o r y .
Similar e f f e c t s
i n d i c a t i n g a s s o c i a t i o n h a v e b e e n d e t e c t e d a l s o w i t h s o l u t i o n s of at-PMMA. I n t h e a p p l i c a t i o n of t h e m e t h o d of t h e r m a l l y s t i m u l a t e d d e p o l a r i z a t i o n c u r r e n t s , p e a k s a r e d e t e c t e d c o n n e c t e d w i t h t h e d e p o l a r i z a t i o n of o r i e n t e d -CO0 d i p o l e s in c o n s e q u e n c e of t h e t h e r m a l motion.
Measurements performed
102 with solid films o b t a i n e d b y p r e c i p i t a t i o n f r o m a m i x t u r e of s o l u t i o n s of i a n d s-PMMA in a c e t o n e h a v e r e v e a l e d a p e a k at 105 - 130°C, a s s i g n e d b y t h e a u t h o r s to Tg in t h e s t e r e o c o m p l e x (ref. 86,87).
With films i s o l a t e d d i r e c t l y
from t h e m i x t u r e s of b o t h s o l u t i o n s a t t h e r a t i o i / s -- I / l , a n a d d i t i o n a l p e a k was d e t e c t e d w h i c h c o r r e s p o n d e d to Tg of f r e e i-PMMA, s u g g e s t i n g c o n c l u s i o n s a b o u t t h e s t o i c h i o m e t r y of t h e s t e r e o c o m p l e x .
Only a p a r t of t h e
s t e r e o c o m p l e x a g g r e g a t e s p r e c i p i t a t e s from a c e t o n e solution; t h e o t h e r p a r t of t h e a g g r e g a t e s r e m a i n s in s o l u t i o n a n d a p p e a r s a s " d i s s o l v e d " ( r e f . 87). 3. DSC. By m e a n s of DSC, t h e m e l t i n g e n d o t h e r m of t h e c r y s t a l l i n e p a r t of t h e s t e r e o c o m p l e x was d e t e c t e d in solid s a m p l e s a n d a t t e n t i o n h a s also b e e n p a i d to t h e m e a s u r e m e n t of t h e g l a s s t r a n s i t i o n t e m p e r a t u r e ( r e f . 35).
For
solid s t e r e o c o m p l e x s a m p l e s o b t a i n e d b y p r e c i p i t a t i o n from s o l u t i o n , t h e e x i s t e n c e of two m e l t i n g e n d o t h e r m s a t =185"C a n d 210°C was d e e t e c t e d ( r e f . 50).
With t h e s t e r e o c o m p l e x p r e p a r e d in b u l k ( a f t e r p r o l o n g e d a n n e a l i n g of
t h e m i x t u r e of i- a n d s-PMMA a t 140°C), o n e m e l t i n g e n d o t h e r m at ~190"C was o b s e r v e d (two e n d o t h e r m s w e r e o n l y o b s e r v e d a t lower c r y s t a l l i z a t i o n t e m p e r a t u r e ) ( r e f . 90).
The a r e a of t h i s e n d o t h e r m d e p e n d s on t e m p e r a t u r e
a n d time of a n n e a l i n g a n d o n t h e r a t i o ( i / s ) in t h e mixture; t h e m e l t i n g p o i n t t e m p e r a t u r e d o e s n o t d e p e n d on ( i / s ) .
The d o u b l e m e l t i n g e n d o t h e r m ,
o r i g i n a l l y a s s i g n e d to t h e c r y s t a l s of s-PMMA a n d to t h e s t e r e o c o m p l e x ( r e f . 50)~ p r o b a b l y c o r r e s p o n d s o n l y to t h e s t e r e o c o m p l e x i t s e l f , p o s s i b l y a s a c o n s e q u e n c e of p r i m a r y a n d s e c o n d a r y c r y s t a l l i z a t i o n ( r e f . 37).
Katime e t al.
( r e f . 51,96) a s s i g n t h e h i g h - t e m p e r a t u r e e n d o t h e r m to t h e s t e r e o c o m p l e x i t s e l f a n d t h e l o w - t e m p e r a t u r e e n d o t h e r m to a g g r e g a t e s stereocomplex.
( c l u s t e r s ) of t h e
B l e n d s of i - a n d at-PMMA p r e p a r e d f r o m a c e t o n e s o l u t i o n
e x h i b i t o n e b r o a d m e l t i n g e n d o t h e r m a r o u n d 150"C ( r e f . 98).
M e a s u r e m e n t s of
Tg i n d i c a t e t h a t b o t h i - p o l y ( e t h y l m e t h a c r y l a t e ) (PEMA) a n d s - p o l y ( i s o b u t y l m e t h a c r y l a t e ) (PiBMA) form c o m p a t i b l e m i x t u r e s in t h e solid s t a t e , p r o b a b l y a s a c o n s e q u e n c e of s t e r e o c o m p l e x f o r m a t i o n in b u l k , with a m e l t i n g e n d o t h e r m a t 153"C (ref. 94). The m e l t i n g e n d o t h e r m was also d e t e c t e d in g e l s f o r m e d b y mixing of c o n c e n t r a t e d s o l u t i o n s of i - a n d s-PMMA in o - x y l e n e (conc. 20% a n d h i g h e r ) (ref. 91,95,97).
It was f o u n d t h a t c r y s t a l l i z a t i o n a n d n u c l e a t i o n in g e l s of
s-PMMA a n d in t h e s t e r e o c o m p l e x is b y s e v e r a l o r d e r s more r a p i d t h a n in i-PMMA.
Consequently, s - P M M A
and the stereocomplex crystallize even
without annealing, which in this case only affects the size distribution of crystals.
T h e similarity in the crystallization behavior of s - P M M A
a n d of the
stereocomplex is considered to be based on the circumstance that in both cases the crystallization behavior is affected b y the short lengths of s-sequences
(ref. 95). T h e quantitative determinations of the heat of melting
103 in PMMA g e l s c a n be c o m p l i c a t e d b y t h e o v e r l a p p i n g v a p o r i z a t i o n of t h e s o l v e n t .
e f f e c t of t h e h e a t of
F r o m t h e m e a s u r e d v a l u e s of t h e h e a t of m e l t i n g
a n d t h e d e g r e e of c r y s t a l l i n i t y , t h e e n t h a l p y of PhIMA s t e r e o c o m p l e x f o r m a t i o n was determined
(AH = - 2 4 J / g )
( r e f . 97); t h i s v a l u e is i n g o o d a g r e e m e n t w i t h
t h e v a l u e s o b t a i n e d b y m i x i n g c a l o r i m e t r y in s t u d i e s of d i l u t e s o l u t i o n s (ref. 93,99). 4. X - r a y d i f f r a c t i o n . T h e f i r s t s t u d i e s of t h e PMMA s t e r e o c o m p l e x h a v e a l r e a d y s h o w n t h a t t h e g e l s f o r m e d b y m i x i n g of c o n c e n t r a t e d a n d s-PMMA in DMF e x h i b i t a c r y s t a l l i n e X - r a y p a t t e r n t h a t f o u n d f o r t h e s o c a l l e d s t e r e o b l o c k ( r e f . 1,83). pattern
s o l u t i o n s of i -
of t h e s a m e t y p e a s
T h e s a m e t y p e of X - r a y
w a s f o u n d a l s o f o r t h e s t e r e o c o m p l e x g e l s in b e n z e n e a n d f o r solid
s a m p l e s of t h e s t e r e o c o m p l e x ( a f t e r r e m o v a l of s o l v e n t ) i s o l a t e d f r o m a c e t o n e , a c e t o n i t r i l e , b e n z e n e a n d o - x y l e n e s o l u t i o n ( r e f . 59,69,95).
The same
d i f f r a c t o g r a m a s t h a t Of t h e s t e r e o c o m p l e x i s o l a t e d f r o m a c t o n e s o l u t i o n w a s a l s o f o u n d f o r t h e s t e r e o c o m p l e x in b u l k o b t a i n e d b y p r o l o n g e d a n n e a l i n g of t h e m i x t u r e of i - a n d s-PMMA ( w i t h o u t s o l v e n t ) a t 140"C ( r e f . 90).
The
v a l u e s of t h e c r y s t a l l i n i t y of t h e solid s t e r e o c o m p l e x i s o l a t e d f r o m DMF o r o - x y l e n e s o l u t i o n d e p e n d o n t h e m o d e of p r e p a r a t i o n 30%9 r e s p e c t i v e l y , a t m o s t ( r e f . 50,97).
a n d a m o u n t to 40 a n d
These results prove that the
f o r m a t i o n of t h e s t e r e o c o m p l e x i s a t l e a s t p a r t l y c o n n e c t e d w i t h t h e c r y s t a l l i z a t i o n of s e g m e n t s of PMMA c h a i n s . concentrated
s o l u t i o n s of i - a n d s-PMMA in DMF, o r i e n t e d f i b e r s of t h e
stereocomplex have also been prepared the X-ray fiber patterns = 2/1 to 1/2).
( r e f . 33,37,100).
of
L i q u o r i e t al. ( r e f . 33), o n t h e b a s i s of t h e f i b e r
h o w e v e r , some d o u b t s
model of t h e PMMA s t e r e o c o m p l e x ;
have arisen concerning
t h e o r i g i n of t h e r e f l e c t i o n s
to t h e s y d i o t a c t i c c o m p o n e n t ( r e f . 41).
stereocomplex was recently proposed energy
The appearance
d o e s n o t d e p e n d o n t h e r a t i o ( i / s ) (in t h e r a n g e i / s
diffractogram, have proposed a structural
assigned
F r o m t h e g e l s of m i x t u r e s of
A r e v i s e d model of t h e PMMA
based on X-ray diffraction and potential
c a l c u l a t i o n s ( r e f . 100).
Q u i t e r e c e n t l y , it h a s b e e n s h o w n b y X - r a y d i f f r a c t i o n t h a t s-PMMA i s p a r t l y c r y s t a l l i n e o n l y in t h o s e c a s e s w h e n it is i s o l a t e d f r o m a s o l u t i o n w h e r e it h a s b e e n p r e s e n t
in the a g g r e g a t e d
c r y s t a l l i n i t y of s-PMMA p r e p a r e d temperature
s t a t e ( r e f . 22,102).
The
b y e v a p o r a t i o n of s o l v e n t a t r o o m
f r o m o - d i c h l o r o b e n z e n e , t o l u e n e , BACj d i e t h y l k e t o n e o r o - x y l e n e
s o l u t i o n a m o u n t e d to 30-40%; t h e s i z e of t h e c r y s t a l l i t e s w a s 4.6 - 6.5 nm ( r e f . 22,38,95,97,102).
The preparation
of o r i e n t e d f i b e r s of c r y s t a l l i n e
s-PMMA b y a b s o r p t i o n of c h l o r o a c e t o n e o r d i e t h y l k e t o n e v a p o r s 24,100,101) h a s a l s o b e e n d e s c r i b e d .
Intermediate-angle
i n d i c a t e s t h e e x i s t e n c e of s p e c i f i c l o n g - r a n g e s-PMMA ( r e f . 23).
(ref.
X-ray scattering
i n t e r a c t i o n s in a s o l u t i o n of
104 5. E l e c t r o n m i c r o s c o p y . T h i s m e t h o d w a s a p p l i e d in a s t u d y of s-PMMA ( r e f . 22).
A p r i n c i p a l l y d i f f e r e n t m o r p h o l o g y of s-PMMA s a m p l e s i s o l a t e d f r o m
various solvents was observed
w h i c h d e p e n d o n t h e e x i s t e n c e or
n o n - e x i s t e n c e of s e i f - a g g r e g a t i o n e f f e c t of t e m p e r a t u r e
of s-PMMA i n t h e r e s p e c t i v e
solvent.
The
o n t h e s t a b i l i t y of t h e r e s p e c t i v e m o r p h o l o g y w a s
investigated.
C. M e t h o d s of m o l e c u l a r s p e c t r o s c o p y
(NMR s p e c t r o s c o p y , v i b r a t i o n a l
spectroscopy 1. N___MRS p e c t r o s c o p y . spectroscopy
The paragraph
c o n c e r n i n g t h e p o s s i b i l i t i e s of NMR
in s t u d i e s of a g g r e g a t i o n of s t e r e o r e g u l a r
somewhat more detailed t h a n the p r e c e d i n g
PMMA will be
paragraphs,
e x p l a n a t i o n s of t h e b a s i c p o s s i b i l i t i e s of t h i s m e t h o d .
especially in This is c a u s e d by the
c i r c u m s t a n c e t h a t t h i s m e t h o d c a n y i e l d a lot of i n f o r m a t i o n n o t o b t a i n a b l e o t h e r w i s e ; a t t h e s a m e time, t h e a p p l i c a t i o n of NMR s p e c t r s o c o p y
in t h i s f i e l d
is n o t v e r y w i d e s p r e a d to d a t e . T h e a s s o c i a t i o n of s t e r e o r e g u l a r
PMMA { i n c l u d i n g s t e r e o c o m p l e x f o r m a t i o n )
h a s b e e n s t u d i e d b y v a r i o u s t e c h n i q u e s of NMR s p e c t r o s c o p y .
In h i g h
r e s o l u t i o n 1H NMR s p e c t r a , PMMA s t e r e o c o m p l e x f o r m a t i o n i s m a n i f e s t e d b y t h e r e d u c t i o n of i n t e n s i t y of all p o l y m e r b a n d s s o m e c a s e s to a c o m p l e t e d i s a p p e a r a n c e Self-aggregation
( r e f . 65,69,103,104), l e a d i n g i n
of t h e s p e c t r u m
(Fig. 7).
of i - o r s-PMMA is m a n i f e s t e d in h i g h r e s o l u t i o n 1H NMR
s p e c t r a in a s i m i l a r w a y (ref. 2,3,54,109).
Similar b e h a v i o r h a s b e e n o b s e r v e d
a l s o w i t h a n u m b e r of o t h e r a s s o c i a t e d p o l y m e r s y s t e m s ; t h e s e f i n d i n g s a r e b r i e f l y s u m m a r i z e d in r e f . 117.
T h e r e d u c t i o n of i n t e n s i t i e s is e v i d e n t l y
c a u s e d b y a d e c r e a s e of p r o t o n m o b i l i t y i n a s s o c i a t e d s t r u c t u r e s v a l u e s t h a t t h e w i d t h of t h e c o r r e s p o n d i n g hundreds
NMR l i n e s i s of t h e o r d e r of
of Hz o r m o r e , so t h a t t h e s e p r o t o n s e s c a p e d e t e c t i o n in h i g h
r e s o l u t i o n NMR s p e c t r a .
The observed
h i g h r e s o l u t i o n NMR s p e c t r u m
e x a m p l e , Fig. 7b) i n t h e s e s y s t e m s c o r r e s p o n d s units.
to s u c h
(see, for
to n o n - a s s o c i a t e d m o n o m e r
T h e r e f o r e , f r o m t h e d y n a m i c p o i n t of v i e w , t h e NMR s p e c t r a of PMMA
solutions, where aggregation
t a k e s place, can in principle be a n a l y z e d as
two-component systems, with one component corresponding
to a s s o c i a t e d u n i t s
a n d t h e o t h e r to n o n - a s s o c i a t e d u n i t s (ref. 3,103,104). A g g r e g a t i o n c a n b e f o l l o w e d q u a n t i t a t i v e l y f r o m m e a s u r e m e n t s of t h e integrated
i n t e n s i t i e s of h i g h r e s o l u t i o n NMR b a n d s
2,3,38,47,54,102-104,108-110).
The integrated
(ref.
b a n d i n t e n s i t i e s I in s y s t e m s
w h e r e a s s o c i a t i o n o c c u r s a r e g i v e n b y t h e r e l a t i o n ( r e f . 3,118):
I -- K ' N n ( T ) ' ( I / T ) ' a l / 2
(1)
105
I I
6
7
8
9
IE in ppm
F i g . 7. H i g h r e s o l u t i o n 1H NMR s p e c t r a o f s a m p l e s o f PMMA i n C6D 6 a t i d e n t i c a l i n s t r u m e n t s e t t i n g s a n d 27°C" (a) s - P M N A - 1 (S = 8 8 . 5 ~ , H ; 9%}; (b) m i x t u r e i - P N M A (I = 97%, H = 3%) + S - P N M A - 2 (S = 69%, H = 27.5%) (1:2); (c) m i x t u r e i-PMMA + s - P M M A - 1 (1:2) ( r e f . 103). where
K is a constant,
non-associated the absolute without
temperature
association,
analogous
Nn(T) is the temperature-dependent
nuclei in the unit volume contributing
and a is the so called saturation
integrated
band
unit volume which contribute possible
intensities,
to Eq. 1, w i t h N n s u b s t i t u t e d
to d e t e r m i n e
is the number comparison
number
to t h e g i v e n
band.
By means
of associated
T is
In systems
by a relation
b y No, t h e t o t a l n u m b e r
to t h e g i v e n
the fraction
of associated
factor.
Io, a r e g i v e n
of band,
of nuclei in
o f E q . 1, it i s
nuclei, p = Na/N o (where
Na
n u c l e i i n u n i t v o l u m e , No = Na + Nn) b y d i r e c t
of integrated
intensities
at negligible
saturation
(a -~ 1) a n d
temperature,
instrument
settings)
of high
resolution
NMR s p e c t r a
under
identical
conditions
with and
without
association:
measured
{concentration,
p : 1 - I / I o.
(2)
As in aggregation intensities corresponds
can be revealed
decreases
the temperature
dependence
dependence
s - P M M A (of h i g h demonstrating temperature
without
with increasing structures
of the integrated of integrated
of the fraction
stereoregularity)
band
behavior,
the value,
p,
monomer units.
also from the temperature
the decomposition range
of associated
of associated
by an increase
PMMA, t h e i n t e g r a t e d
exhibit identical
While i n s y s t e m s
monotonously
Eq. 1, t h e d e c o m p o s i t i o n
temperature
groups
to t h e f r a c t i o n
intensities.
will b e s h o w n
of stereoregular
proton
directly
Association integrated intensity
studies
of various
dependence
association temperature,
according
with increasing intensity
intensity
and
I.
of
the integrated to
temperature
As an example,
the corresponding
p for a mixture of solutions
of i- and
i n D M F - d 7 i s s h o w n i n F i g . 8, (melting) of stereocomplex
50 - 120"C ( s e e r e f . 105).
aggregates
in the
106
i
50
8 O o
c r-
nt~
)
-60
I
40 30 20
201 Fig. 8. T e m p e r a t u r e IH NMR s p e c t r a (o) m i x t u r e s o f i-PMMA m i x i n g r a t i o r -- 1.2
I
I
50
100
\
-
- 150 t e m p e r e t u r e , "C
d e p e n d e n c e of the i n t e g r a t e d i n t e n s i t y in h i g h r e s o l u t i o n a n d f r a c t i o n of a g g r e g a t e d m o n o m e r u n i t s p (e) f o r (I = 91%; H -- 7%) a n d s-PMMA (S = 85%; H = 12%) w i t h i n DMF-d 7.
By m e a n s o f t h e v a l u e s of t h e a s s o c i a t e d
fraction
followed.
I n t h i s w a y , t h e e f f e c t of s o l v e n t , r a t i o ( i / s ) , s t e r e o r e g u l a r i t y ,
studied found
factors
from high
IH NbIR s p e c t r a ,
and thermal history
the effect of various
p determined
resolution
on association can be
o n t h e f o r m a t i o n o f PMMA s t e r e o c o m p l e x a g g r e g a t e s
and their thermal stability was characterized
( r e f . 103,104).
t h a t i n t h i s c a s e t h e v a l u e s of p a r e p r a c t i c a l l y
independent
molecular weight
(if t h i s is h i g h e r
relatively weakly dependent
than a certain
on concentration
time was
It was of
limit) ( r e f . 103) a n d
( r e f . 119). T h u s , i d e n t i c a l v a l u e s
of p w e r e f o u n d
f o r m i x t u r e s o f i - a n d s-PMMA i n C6D6, w i t h a
number-average
m o l e c u l a r w e i g h t o f s-PMMA e q u a l t o 44000 in o n e c a s e a n d
t o 2600 i n a n o t h e r
(stereoregularity
of b o t h s-PMMA s a m p l e s w a s i d e n t i c a l ) .
A weak effect of molecular weight was also p rove d self-aggregatior/.
While f o r a n o - d i c h l o r o b e n z e n e
65%; H = 31%; I = 4%) of ~ stereoregularity
i n t h e c a s e o f s-PMMA s o l u t i o n o f at-PMMA (S =
= 45,000, p = 0, f o r at-PMMA of t h e s a m e
b u t m o l e c u l a r w e i g h t of a b o u t o n e million, in t h e s a m e
s o l v e n t p : 9% ( r e f . l l 9 ) .
The effect of conce ntra tion
detail for mixtures of i- and
was studied
s-PMMA i n t o l u e n e - d 8 ( r e f . I 1 9 ) .
in g r e a t e r
Although the
v a l u e s o f p f o r c = 0.2% (p =76%) a r e l o w e r t h a n f o r c = 10% (p : 93%), it i s
107 e v i d e n t t h a t e v e n in f a i r l y d i l u t e s o l u t i o n s t h e i - a n d s - P M M A in m u t u a l i n t e r a c t i o n .
concentration and stereoregularity also characterized determined
on s e l f - a g g r e g a t i o n
( r e f . 2,3,38,47,54,102,109,110).
(ref. 38,54).
was
By m e a n s of NMR s p e c t r o s c o p y ,
the
f o r m a t i o n in t o l u e n e - d 8 a n d in BAC w a s a l s o
M e a s u r e m e n t s of the i n t e g r a t e d
r e s o l u t i o n 1H NMR s p e c t r a w e r e u s e d to c h a r a c t e r i z e the diner
of i - o r s-PMMA w a s
a n d t h e t h e r m a l s t a b i l i t y of t h e s e l f - a g g r e g a t e s
k i n e t i c s of s-NMMA s e l f - a g g r e g e studied
molecules are
By m e a s u r e m e n t o f t h e p - v a l u e s , t h e e f f e c t of s o l v e n t ,
model of PMMA, t h e d i m e t h y l e s t e r of
i n t e n s i t i e s of h i g h the interaction between
2,2,4,4-tetramethylglutaric
a c i d (DMTMGA) a n d i - o r s-PMMA (ref. 108). B e s i d e s t h e v a l u e s of p, b a s e d o n d i r e c t m e a s u r e m e n t of t h e s i g n a l of non-associated units, further d y n a m i c s of a g g r e g a t e d aggregated
information concerning the structure
and
s e g m e n t s c a n be o b t a i n e d b y t h e m e a s u r e m e n t of t h e
c o m p o n e n t b y b r o a d - l i n e NMR s p e c t r a , t h e m e a s u r e m e n t of
non-selective relaxation times with a pulse spectrometer and by the a p p l i c a t i o n of the t e c h n i q u e s of m e a s u r e m e n t of s o l i d - s t a t e h i g h r e s o l u t i o n spectra.
I n o u r s t u d i e s of t h e a s s o c i a t i o n of s t e r e o r e g u l a r
we h a v e u s e d two s u c h m e t h o d s ; i.e., 1H NMR s p e c t r a magic-angle spinning
(MAS) a n d 13C NMR s p e c t r a
p r o t o n d e c o u p l i n g (ref. 104,106,110).
m e a s u r e d with s t r o n g
W h e n t h e b r o a d e n i n g of b a n d s of n u c l e i
in a s s o c i a t e d s e g m e n t s is c a u s e d b y n e a r - s t a t i c the spinning frequency
PMMA i n s o l u t i o n ,
measured with
dipolar interactions and when
v r in 1H NMR s p e c t r a o r t h e i n t e n s i t y of t h e
d e c o u p l i n g field YH2/2~ i s s u f f i c i e n t l y h i g h { l a r g e r t h a n t h e w i d t h of t h e p r o t o n b a n d i n t h e c o n v e n t i o n a l l y m e a s u r e d s p e c t r u m ) , a p p l i c a t i o n of t h e s e t e c h n i q u e s c a n l e a d to t h e n a r r o w i n g of t h e b r o a d b a n d of t h e a s s o c i a t e d s e g m e n t s a n d to t h e a p p e a r a n c e
of a h i g h r e s o l u t i o n NMR s p e c t r u m .
Thus,
a l r e a d y t h e s i m p l e s t a t e m e n t a b o u t t h e e f f e c t i v e n e s s of t h e s e t e c h n i q u e s contributes
to t h e c h a r a c t e r i z a t i o n of n o t i o n a l h i n d r a n c e in t h e a s s o c i a t e d
s e g m e n t s { p r e s e n c e o r a b s e n c e of n e a r - s t a t i c In stereocomplex gels generated of h i g h s t e r e o r e g u l a r i t y
dipolar interactions).
b y m i x i n g o f s o l u t i o n s o f i - a n d s-PMMA
a n d i n s-PMMA s e l f - a g g r e g a t e s
in t o l u e n e - d s , the
b r o a d e n i n g of b a n d s of a s s o c i a t e d s e g m e n t s i s n o t c a u s e d b y n e a r - s t a t i c dipolar interactions~ but by the reduced
v e l o c i t y of t h e e f f e c t i v e l y i s o t r o p i c
m o t i o n of t h e m a i n c h a i n ( r e f . 106,110).
In this respect, these systems
q u a l i t a t i v e l y d i f f e r from the swollen gels of chemically c r o s s l i n k e d p o l y m e r s where large linewidths are connected with rapid internal motions restricted s p a c e ( r e f . 120); in c h e m i c a l l y c r o s s l i n k e d g e l s , t h e s p a t i a l r e s t r i c t i o n of m o t i o n of m o s t m o n o m e r u n i t s i s a c o n s e q u e n c e of t h e e x i s t e n c e of a r e l a t i v e l y s m a l l n u m b e r of s t a t i c e r o s s l i n k p o i n t s .
The observed
different
b e h a v i o r i n d i c a t e s t h a t i n t h e f o r m a t i o n o f t h e PMMA s t e r e o c o m p l e x a n d in self-aggregation
of s-PMMA a d i r e c t c o n t a c t of l o n g c h a i n s e g m e n t s t a k e s
in
108 place and
that
the number
considerable. the fraction fraction
NMR s p e c t r o s c o p y stereocomplex,
(i/s).
segments
with other
In connection
formation,
the relaxation
Overhauser
factors,
structure
o f PMMA ( r e f . 29).
relaxation
p on
and in
measured
by the
differences
alone; the same is true
were
shape
for
o f 13C T 1 with cross
( r e f . 107).
as compared
the general
measured
the effect of solvent
13C MAS NMR t e c h n i q u e
were observed
concerning
t i m e s T 1 o f 1H
The values
(CP) f o r t h e s o l i d PMMA s t e r e o c o m p l e x
no remarkable
p in
of the fraction
associated
s-PMMA with the aim of determining
times were
observations,
o f NMR s p e c t r o s c o p y
on the conformational
polarization
of the
o f IR a n d
methods.
with stereocomplex
of i- and
measure
of the fraction
dependence between
advantage
13C n u c l e i , a s w e l l a s t h e n u c l e a r
solutions
i n Eq. 2 a s
In the case of the
by further trends
the sharp
is a great
a realistic
VI-A).
of the temperature and
is
p defined
(see also comparison
is also supported
T h e a b i l i t y to d i f f e r e n t i a t e
non-associated comparison
represent
contact
in the following text, Part
this conclusion
monomer units
of the fraction
thus
in direct
on stereoregularity
the ratio
and
units
by the character
depedence
interacting
high values
of the less mobile units
of associated
especially
of mutually
The observed
In this case,
to i - a n d of the
s-PMMA
13C CP MAS NMR
spectra.
2. I n f r a r e d suitable
(IR) a n d
method
the given
Raman sDectroscopy.
for studies
case for the detection
consequence
of association.
aggregation
of stereoregular
in studies
of solid samples
has shown
that
stereocomplex intensity
assigned
the shape
Various
and
intensity
bands
The authors
the dynamics
methyl
of the ester
the intensities
of the doublet
conformational
structure
formation manifested
by an increase
tendency
remains
situation
is illustrated
preserved
vibrations
o f t h e PMMA
that
changes
and
they
resemble
in terms
attention
to t h e
that
the is
even
in the solid state
a t 860 cm - 1 a n d
(ref. 21,22,113).
the spectra
of
w a s p a i d to
sensitive
It was observed
of the band
(ref.
(~1450 cm - 1 )
from the shape
these
and
studied.
as well as of the s-PMMA aggregates,
of the intensity
in
of
solutions
were
860 c m - 1 w h i c h a r e
i n F i g . 9, w h i c h e x h i b i t s
s o l i d PMMA s t e r e o c o m p l e x
bands
Considerable
o f s - P M M A ( r e f . 21).
of the stereocomplex,
group
of at-PMMA but
interpret
a t 843 a n d
from these
o f IR s p e c t r a
of these
group.
in
structure
both in studies
considerably
i n CC14 s o l u t i o n s
s o l i d a t - P M M A ( r e f . 114).
is a
of polymers,
(ref. 21,22,102,111,114,116}
methyl
i n CC14 ( c o n c . 1%) d i f f e r
of these
used
isolated
ranges
to t h e e s t e r
spectroscopy
structure
of conformational
were
PMMA i n s o l u t i o n
of the structure
of bands
of changes
IR s p e c t r a
21,22,101,102,111-113,115,116}. Analysis
Vibrational
of the conformational
this
This
of s-PMMA in the
(A), o f s - P M M A i n N u j o l m u l l (B) a n d o f s - P M M A
109 films isolated or does
stereocomplex change
from media where
{D,E) t a k e
place.
formation
two different
for the conformational addition
to t h e a b o v e
manifested carbonyl
and
especially stretching
structure
by the appearance
22,102,111).
This ordering
polymerization measurements stability
is preserved
aggregation
takes
place
in aggregation-promoting of the temperature
solid s-PMMA was characterized conformational
structure
with a
Based on measurements r e f . 21,22) w e r e
of new bands
groups
in t h e r a n g e
of
(ref. from
(ref. 22,102,111) or prepared
and
( r e f . 21,22).
of s-PMMA in solution
( r e f . 115).
o f IR s p e c t r a , of the ordered
is
in
in the aggregates
in solid s-PMMA isolated
dependences
proposed
In
1727 c m - 1 ( w e a k )
solvents
o f t h e s o l i d PMMA s t e r e o c o m p l e x
both
of s-PMMA in solution
a t 1742 cm - 1 a n d of ester
that
in the stereocomplex.
self-aggregation
vibrations
d o e s n o t (C)
indicate
are connected
of s-chains.
of s-chains
changes,
of mutual ordering
where
shown
m o d e l s {cf. r e f . 113 a n d
structure
consequence
solutions
of the polymer
which are
s-PMMA self-aggregation
of the conformational
o f IR s p e c t r a ,
self-aggregation
The changes
by
From the thermal structures
The effect of solvent was also studied
in
on the
( r e f . 21,22,29).
E
o
.o
!
g00
850
cm-1 800
Fig. 9. Part of IR spectrum of B-PMMA (S : 89.5%; H : 8.5%) films. Spectrum of s-PMMA in film of PMMA stereocomplex (i.e., normalized difference of
spectra of stereocomplex and i-PMMA) (A) and of B - P M M A in Nujol mull (B); spectra of s - P M M A films prepared by evaporation of solvent from s - P M M A in acetonitrile (C), o-dichlorobenzene (D) and toluene (E) at 25"C. All spectra measured at 25"C (ref. 22).
110
T h e solid PMMA s t e r e o c o m p l e x w a s a l s o s t u d i e d b y R a m a n s p e c t r a 21).
(ref.
Also b y t h i s m e t h o d , it w a s f o u n d t h a t t h e i n t e n s i t i e s of t h e b a n d s of
t h e s t e r e o c o m p l e x a r e n o t a n a d d i t i v e s u m of t h e i n t e n s i t i e s of t h e i - a n d s-components.
Raman spectroscopy
has also contributed
t h e o r i g i n of t h e s p l i t t i n g of t h e c a r b o n y l s t r e t c h i n g d i p o l e c o u p l i n g of e s t e r g r o u p s ) i n o r d e r e d
V.
FORMATION
AND CHARACTER
d e p e n d s on a n u m b e r
vibration (transition
s e q u e n c e s of s-PMMA (ref. l l l ) .
OF AGGREGATES
T h e formation and character of P M M A
to t h e e x p l a n a t i o n of
OF PMMA
stereocomplex aggregates in solution
of factors; e.g.: I) on the ratio i/s in the mixture; 2)
on the degree of stereoregularity of the components; 3) on temperature; 4) on the time from the mixing of the components; 5) on thermal history; a n d 6) on solvent.
If w e exclude the ratio i/s in the mixture, then the same factors
also affect self-aggregation of s - P M M A .
In the following text, the effects of
each of these factors will be discussed separately.
However, it has to be
kept in mind that in reality all these factors act as a complex and it m a y cause some difficulties to separate their effects.
After the paragraph
devoted to the question of the stoichiometry of the stereocomplex, all three forms of aggregation of stereoregular P M M A self-aggregates of i- and s - P M M A )
(i.e., stereocomplex and
will be discussed in parallel in the
following p a r a g r a p h s in order to stress the similarities a n d also the differences existing between these three forms. A. Stoichiometry of P M M A A large n u m b e r
stereocomplex
of papers (often presenting very differing views) were
devoted to the problem of the stoichiometry of the stereocomplex. Chiang eL al. (ref. 40) (based on sedimentation measurements)
While
conclude that
no defined stoichiometry of the stereocomplex exists, other authors a s s u m e parallel existence of sterecomplexes of the composition i/s = 2/1, i/I a n d 1/2 (ref. 34,41), while the remaining papers advocate stereocomplex formation at a given ratio i/s. Most papers find the stoiehiometry i/s = 1/2 (ref. 33,35,37,39,48,56,65,86,87,92) but papers indicating the stoichiometry i/s = i/I also exist (ref. 49,50,59,60,66,70).
At the same time, the possibility of
stereocomplex formation in the ratio i/s = 1/2 is also not excluded, assuming its generation from the primary complex with i/s = I/I in the presence of free s - P M M A
in the system (ref. 49,50,59).
T h e values cited above of the
ratio i/s refer to the weight ratio of both c o m p o n e n t s and not to the ratio of chains (sequences) in mutual interaction.
Therefore, there is no reason w h y
the stoichiometric ratio should be given only b y whole n u m b e r s I/2.
T h e results of N M R
as I/I or
spectroscopy a n d mixing calorimetry indicate i/s =
1/1.5 (ref. 103) a n d intermediate between i/s = 1/1.5 to I/2 (ref. 93), respectively.
111 The contradictory results concerning the stoichiometry of the stereocomplex
can have a number
of reasons
and
some of these
we s h o u l d
l i k e to p o i n t o u t n o w : (i) I n o u r o p i n i o n , a n u m b e r imperfect
stereoregularity
is not specified stereocomplex interactions depends
evident quantity
quantities authors
where
turbidity,
molecular
( r e f . 66,93} t r y
weight)
attains
Similar difficulties
contains
short
may appear
sequences
radical
polymerized
s-triads.
the weight
However, even
PMMA.
stereoregularity
this procedure
on the example of conventional
triads
it c a n n o t
in stereospecific
(units
marked
be excluded
interaction
component
by an asterisk that
even
respectively).
to u s e s a m p l e s
of i- and
certainly
in only several
higher
papers
the weight
s-PMMA in stereocomplex 90%; h o w e v e r ,
associated sequences
f .J.
LDLDLDL IDDDDLDLDIDLDLD IDL - s-PMMA DDD DDD
IDDDD_ I_PMMA
studies
participate
( r e f . 103) t h a t
the
to i s o t a c t i c
fractions
these
this condition
(ref. 34,35,37,50,56,65,103).
.I. .l.
below).
in t h e s c h e m e ) .
indicate compared
T h e o n l y w a y to e x c l u d e
than
scheme
can directly
m a x i m u m to a h i g h e r
Xi a n d Ys a r e
If the
r a t i o , we e l i m i n a t e t h e
suggested
component
l e a d s to a s h i f t o f t h e a s s o c i a t i o n
s-components,
units
as
PMMA (S ~
are present.
in our
these
o f NMR s p e c t r o s c o p y
of syndiotactic
m i x i n g r a t i o r (r : Y s / X i , w h e r e
tacticity,
for the weight
(e.g., in the manner
At t h e s a m e t i m e , t h e r e s u l t s lower stereoregularity
sequences
by
is problematic
only short
is substituted
Some
ratio of both components
practically
s-triads
also in
in non-negligible
to e l i m i n a t e t h e e f f e c t o f i n s u f f i c i e n t
PMMA b y r e p l a c i n g
a minimum or
specifically
heterotactic
it is
ratio of i- and
60%; H -- 30%), w h e r e
However,
which
contain
can be demonstrated
ratio of i- and
text,
one, then
to t h e s t o i c h i o m e t r i c
as is the case in conventional
the ratio of i- and
minimum length
to t h e p r e d o m i n a t i n g
sequences.
the polymer
of the interacting
in further
of intermolecular
If one or both components
opposite
not correspond
in the associated cases
a certain
by
ratio of i- or s-PMMA in the mixture at which some
(e.g., viscosity, need
can be caused
which in some papers
A s will b e s h o w n
than
of solvent.
the weight
results
polymers
place in consequence
longer
of configuration
maximum value
those
takes
of sequences
that
s-units
a t all ( r e f . 33,39,40).
formation
on the type
sequences
of contradictory
of the interacting
value of of i- and
complications
of possibly has been
is
highest fulfilled
112 (ii) S o m e a u t h o r s where
assume
the measured
the stoichiometry
quantity
reaches
33,48).
Mixtures
studied
a t all ( r e f . 3 5 , 6 0 , 6 5 , 8 7 ) .
quantity
with values
in dependence
distinction
between
i/s = 1/2 even
in those
cases
a m a x i m u m a t t h e r a t i o r = 1.5 ( r e f .
of r between
r = 1 to 2 w e r e
The observed
extreme
o n Ys s o m e t i m e s i s n o t s h a r p
the stoichiometries
i/s
sometimes
not
of the measured enough
to permit
= 1.5 o r 1 / 2 { r e f .
33,35,39,50,56,70,92). (iii) T h e o b s e r v e d that
differences
in some methods
measured
quantity
participating
is not directly
in stereocomplex
r need
not signify
ratio.
In other
differing
values
observed
that
that
various
quantities
Actually,
Kusakov
anisotropy t o r = 1. to other
associated
(p) a n d
differentiation
and
the components. spectra
of mixtures values
shown
determination
by the measurement
of solutions
of highly
of the stereocomplex
of solutions
i n F i g . 10.
of i- and
A comparison
a t r = 2, t h e m i n i m u m
of the stoichiometry
of the
of the
in the mixture; and
of the extent
of the ratio of components
at somewhat
( r e f . 60) h a v e
1) d i f f e r e n t i a t i o n
fractions
in this
of the aggregates
s-PMMA in the non-associated
Therefore,
various
stoichiometry
thus
in studies
(l-p)
extremes
Mekenitskaya are formed
make possible:
at some value
is stoichiometric
maximum ordering
used
non-associated
of i- and
chemical shifts)
mixtures
methods
1H NMR s p e c t r a
etc., the
of units
observed
could exhibit and
aggregates
indicating
to t h e n u m b e r
stereocomplex
of r.
of segmental
light scattering,
An extreme
words,
corresponds Contrary
proportional
heaviest
by the circumstances
turbidimetry,
formation.
the associated
while the
stereocomplex,
can also be caused
like viscometry,
part
stereoregular
(by differing
of association
of high
resolution i- and
can be obtained
( r e f . 103).
of lines corresponding
L
L
I
I
6
'7
8
9
of each of 1H NMR
s-PMMA at
r, reliable information
s - P M M A i n C6D 6 a t v a r i o u s
2)
on the Spectra
of
values
of r are
to i- and
s-PMMA
J
10 -r in ppm
F i g . 10. H i g h r e s o l u t i o n 1H NMR s p e c t r a o f m i x t u r e s o f s o l u t i o n s o f i-PMMA (I = 97%, H = 3%) a n d S - P M M A (S = 88.5%, H = 9%) i n C6D 6 w i t h m i x i n g r a t i o r = l(a), r = 1.5(b), r = 2(c). T h e s p e c t r a w e r e m e a s u r e d a t 27"C a l o n g t i m e after the mixing of both components, with identical instrument setting (ref. 103).
113 indicates
that
corresponds high
for r = 1 the residual predominantly
resolution
spectrum ratio.
NMR s p e c t r u m
of the mixture
high
resolution
to n o n - a s s o c i a t e d
NMR s p e c t r u m
i-PMMA; a t r = 2, t h e r e s i d u a l
is predominantly
that
w i t h r = 1.5 c o r r e s p o n d s
of s-PMMA.
At t h e s a m e t i m e , t h e t o t a l v a l u e o f p i s h i g h e s t
a t r = 2, p = 85%; w h e r e a s
a t r = 1, p = 75%.
also for mixtures
s - P M M A i n CD3CN, w h e r e
of i- and
spectrum
f o r r = 1 (p : 85%) c o r r e s p o n d s
67%} a n d
r = 4 ( p : 48%) o n l y to s - P M M A .
1 a large
part
confirmed currents
o f i-PMMA e x i s t s
also by measurements
stereocomplex
high
resolution
indicates
that
are always i/s
part
in mixtures
of mixing where units
the measured
incorporated
composition methods,
lies between
The formation
individual
high
used
is i/s
to t h e n u m b e r
that
only a very
mainly by the distribution
of
the stereocomplex
in associated
of the degree
i- and
both
has s-sequences
extreme
of a~gregates
of stereoregularity
of the
For the s-component, ( r e f . 103).
o f i-PMMA (I = 97%, H : 3%, S = 0) o f components
i n T a b l e 2.
table, it is evident
increases
considerably
All t h e s y n d i o t a c t i c
of ieotactic
of the syndiotactic
of different
From this
monomer units
of s-PMMA.
small number
of
o f 1H NMR s p e c t r o s c o p y
with syndiotactic
of associated
values}.
of quantitative
of stereo-association.
mixtures
of
the
of various
by means of the interaction
by the application
stereoregularity
that
= 1/2.
to t h e i m p o r t a n c e
i n C6D 6 a r e g i v e n
segments
of the heats
only one type
i/s = 1/1.5 to 1/2 (including
of p for several
i n C6D 6 t h e c o n t e n t
contain
that
to s u m m a r i z e
in studies
stereoregularity
with increasing
proportional
By a combination
its stoichiometry
of the effect
stereoregularities that
= 1.5 to 1 / 2 .
points
was solved
The values
from measurements
is roughly
of the stereocomplex
components
this problem
p values,
r, the associated
of stereoregularity on the formation of a~re~ated sequences}
sequences
characterization
method,
with the ratio of units
in the interval
stereoregular
i/s
it is possible
B. E f f e c t o f d e g r e e (minimum length
very
and
stoichiometry,
somewhere
The composition
from the residual
with the ratio of monomer units
e t al. ( r e f . 37) c o n f i r m
exists
It seems that unique
of a primary
i n t h e c o m p l e x , B i r o ~ e t al. ( r e f . 93) c o n c l u d e
Vorenkamp
stereocomplex
(cf, r e f . 4 9 , 5 0 , 5 9 ) .
composition
with r =
depolarization
the existence
as determined
s-sequences
value
NMR
was recently
with the corresponding
of different
By a further
resolution
in mixtures
state
stimulated
against
= 1/1
together
of i- and
= 1 / 1 . 5 ( r e f . 103}.
The fact that
of the mixture,
NMR s p e c t r u m
composed
argues i/s
were observed
the high
to o n l y i-PMMA, f o r r = 2.5 (p =
of thermally
with a composition
of the non-associated
to t h e m i x i n g
a t r = 1.5 (p = 89%};
Similar results
in the non-associated
( r e f . 86,87}; t h i s c l e a r l y
T h e NMR
approximately
triads
sequence
and
polymers
they
lengths.
differ
It can be
114 TABLE 2 F r a c t i o n of a s s o c i a t e d m o n o m e r u n i t s p a n d m i n i m u m l e n g t h s - s e q u e n c e s f o r s o m e m i x t u r e s o f i - a n d s-PMMA in C6D 6
T y p e of s y n d i o t a c t i c
component a
Mixing r a t i o b
p
r = Ys/Xi
s-PMMA
- I
(I = 2.5%; H:9%; S : 88%.5%; :Is = 20°7)
s- PMMA
q of a s s o c i a t e d
(%)
q (in m o n o m e r u n i t s )
i
75
9
1,5
89
9
- II
2
55
8-9
2
35-40
10
.%0
io-ii
(I : 3.5%; H = 27.5%; S : 69%; :is = 6.0)
s-PMMA - I I I (I = 3.5%; H : 31.5%; S : 65%; :Is = 5.1)
1.5
aI,H,S - d e n o t e t h e f r a c t i o n of i s o t a c t i e , h e t e r o t a c t i c a n d s y n d i o t a c t i c r e s p e c t i v e l y ; Ts = {2S + H ) / H i s t h e m e a n s y n d i o t a c t i c l e n g t h .
triads,
b _ w i t h i-PMMA (I = 97%; H = 3%; S = 0).
assumed
that there
exists a certain
sequences
w h i c h is n e c e s s a r y
associated
segments
minimum length
of s t e r e o r e g u l a r
for stereocomplex formation and that the
are separated
by non-associated
sequences
of t h e
macromolecules. A syndiotactic sequence
sequence
isotactic step.
assuming first-order sequences
m w h i c h can follow a f t e r an i s o t a c t i c
(Bis(m)) or a f t e r a s y n d i o t a c t i c
the original syndiotactic
illustrated
of l e n g t h
step is repeated
Isotactic sequences
sequence
( B s s ( m ) ) is d e f i n e d
so that
are defined
similarly; the s y s t e m is
by the following example:
that the polymers can be described blarkov statistics, containing
m units
by Bernoulli statistics
or by
the w e i g h t f r a c t i o n ws(m) of s y n d i o t a c t i c is g i v e n b y t h e r e l a t i o n ( r e f . 103,121):
115
2 ws'm'~) = m P s - Pisl~ 1
m-I
" PsiPss
, m • 2
.
(3)
I n t h i s e q u a t i o n , P s i s t h e p r o b a b i l i t y of s y n d i o t a c t i c a d d i t i o n , P s s is t h e p r o b a b i l i t y o f s y n d i o t a c t i c p l a c e m e n t to a s y n d i o t a c t i c d i a d a n d t h e p r o b a b i l i t i e s Psi a n d Pis a r e d e f i n e d in a n a n a l o g o u s way.
The probabilities
obey the following relations:
A/2 Ps
= S + H/2;
Psi
= S + H/2
H/2
.
'
Pis
S
= I + H/2
;
T h e w e i g h t f r a c t i o n of all s y n d i o t a c t i c s e q u e n c e s
Pss
(4 )
- S + H/2
is g i v e n b y t h e
r e l a t i o n ( r e f . 103,121):
1 fs(1)
= Ps
' Pss
+Psi
(5)
" 1 - PisPsi
F r o m a c o m p a r i s o n of t h e f o u n d v a l u e s of p w i t h t h e d i s t r i b u t i o n o f s y n d i o t a c t i c s e q u e n c e l e n g t h s , ws(m) , t h e m i n i m u m l e n g t h q of a s s o c i a t e d s y n d i o t a c t i c s e q u e n c e s c a n b e c a l c u l a t e d b y m e a n s of t h e r e l a t i o n ( r e f . 103):
q-I J
(Ys~s)
P = fs(I)
- Z m=2
(6}
Ws(m )
w h e r e Y~ i s t h e f r a c t i o n o f s y n d i o t a c t i c u n i t s i n a s s o c i a t e d s e g m e n t s ( f o r t h e s t o i c h i o m e t r y i / s = 1/1.5, Y~ = 0.6; f o r t h e s t o i c h i o m e t r y i / s = 1/2, Y~ = 0.67}. Eq. 6 i s a p p l i c a b l e f o r Ys ~ Y~, while t h e v a l u e s o f (Y~/Ys)P f o r Y~ -- 0.6-0.67 do n o t d i f f e r a p p r e c i a b l y . The dependence
d of f s ( 1 ) - ~
ws(m} o n t h e s e q u e n c e l e n g t h d f o r s-PHMA
s t u d i e d b y u s is s h o w n i n Fig. 11.
T h e e x p e r i m e n t a l l y f o u n d v a l u e s (Yo'/Ys} p
are indicated by arrows and dashed horizontal lines; the corresponding intercepts
on t h e h o r i z o n t a l axis indicate the v a l u e ( q - l ) .
T h e v a l u e s of q o b t a i n e d b y m e a n s of Eq. 6 f o r t h e m i x t u r e s of i - a n d s-PMMA in C6D 6 a r e s h o w n i n T a b l e 2.
I n all c a s e s , t h e a g r e e m e n t is g o o d ,
i n d i c a t i n g t h a t i n b e n z e n e t h e m i n i m u m l e n g t h of s - s e q u e n c e s a s s o c i a t i o n , q = 8 to 10.
V a l u e s of q a r o u n d
o-dichlorobenzene and benzaldehyde.
necessary
for
10 u n i t s w e r e a l s o f o u n d f o r
F o r m i x t u r e s of i - a n d s - P P M A w i t h r =
2 i n CCI 4, CD3CN a n d i n DMF-d7, a s s o c i a t i o n o f p r a c t i c a l l y all m o n o m e r u n i t s (p ~ 95%) w a s o b s e r v e d
e v e n in t h o s e c a s e s w h e r e the s t e r e o r e g u l a r i t y
s - c o m p o n e n t w a s n o t v e r y h i g h ( s - P M M A - t y p e III i n T a b l e 2). that the minimum s-sequence
length necessary
of t h e
This indicates
for s t e r e o c o m p l e x formation in
116
I
l
l
l
|
l
l
l
l
l
1.0
0.8 %4,", t E "-~ 0.6
0.4
0.2,
I
I
I
4
I tl
tl
I
I
I
I
I
8 12 16 20 d (in monomer units)
d F i g . 11. D e p e n d e n c e o f t h e v a l u e f s ( 1 ) -m-~ w s ( m ) o n t h e s - s e q u e n c e length d f o r s - P M M A - 1 (S = 88.5%, H = 9%) (o); s - P M M A - 2 (S = 69%, H = 27.5%} (•); s - P M M A - 3 (S -- 66%, H = 31%) (o). T h e e x p e r i m e n t a l l y f o u n d v a l u e s (Y~/Ys)P f o r m i x t u r e s o f b e n z e n e s o l u t i o n s o f i-PMMA a n d s - P M M A a r e i n d i c a t e d b y a r r o w s a n d d a s h e d h o r i z o n t a l l i n e s (cf. Eq. 6) ( r e f . 103}. these
solvents
is of the order
q = 3; i n t o l u e n e ,
of q are valid at or below room temperature; temperatures
will b e d i s c u s s e d
The effect of the degree
determined
all t h e s e (proven
stereoregularity,
b y NMR s p e c t r a j
spectroscopy) s-sequences it j u s t i f i e s
the assumption
minimum length where
interaction
take part
prerequisite
i n T a b l e 3.
The finding
that
in aggregation.
that
s-PMbIA-3 does not take
the presence
of self-aggregation;
that only s-sequences
of s-sequences
fraction
of s-PMMA samples
osmometry~ light scattering
( r e f . 22~47,54,111) i n d i c a t e s is a necessary
of the associated
solutions
of conventional
viscometryj
was also
0.2 - 10% ( r e f . 110) a n d
for several
are summarized
media self-aggregation
values
at elevated
on association
The values
in the range
f r o m NMR m e a s u r e m e n t s
of various
the situation
of stereoregularity
of concentration
The quoted
in the following paragraph.
followed for s-PMMA self-aggregation. p, i n d e p e n d e n t
q ~ 4-5.
longer
Contrary
with practically
than
and
IR
of long also, in this case a certain
to the stereocomplex,
perfect
in place
stereoregular
117
TABLE 3 Quantitative
characterization
of ordered
Polymer
s-PMMA b y NMR a n d IR s p e c t r o s c o p y
F r a c t i o n of associated monomer units p f r o m NMR (%)
Solvent
Solution
F r a c t i o n of o r d e r e d s-PMMA f r o m IR a (%)
Solution
Solid State
s-PMMA-I
toluene
85
29
25
(S : 89.5%; H : 8.5%)
o-dichlorobenzene
73
27
29
butyl acetate
ca 90
b
24
s-PMMA-2
toluene
76
b
b
toluene c
0
0
0
(S = 85%; H = 12%) s-PMMA-3 (S = 66%; H = 31%)
adetermined from integrated intensities s t r e t c h i n g v i b r a t i o n s ; c f P a r t VI-A.
after
separation
of b a n d s
o f C=0
bnot measured Cno a s s o c i a t i o n w a s a l s o o b s e r v e d solutions
i-PMMA c h a i n s w a s c o n s i d e r e d , interactions structure
of s - sequences
in o-dichlorobe nz e ne
butyl acetate
i n t h e c a s e o f s-PMMA s e l f - a g g r e g a t i o n
must be considered.
is f o r m e d b y m u t u a l i n t e r a c t i o n
a r e of t h e minumum length
and
If we a s s u m e
of two s-sequences
mutual
that a stable ( b o t h of w h i c h
q or longer), then for the non-associated
f r a c t i o n , w e c a n w r i t e ( r e f . 111):*
1 - p - fi(1)
q-1 = 2 z ws(m ) m=2
Making u s e of the identity a shape
analogous
(7)
fi(1) + f s ( 1 ) = 1, Eq. 7 c a n b e t r a n s f o r m e d
into
to Eq. 6:
*All s - s e q u e n c e s c a n b e m e n t a l l y d i v i d e d i n t o t w o p a r t s ( m a r k e d a s w h i t e a n d black, respectively) with interaction always taking place between white and black sequences. Both parts have the same length distribution and the same m i n i m u m l e n g t h , q. T h e n i n c o n s e q u e n c e o f i m p e r f e c t s t e r e o r e g u l a r i t y , both c o m p o n e n t s p a r t i c i p a t e e q u a l l y in the n o n - a s s o c i a t e d f r a c t i o n of s - s e q u e n c e s , 1 - p - fi(1).
118
q-1 p = fs(1) - 2 ~ Ws(m). m=2
(8)
d For the studied polymers, the plots of fs(1) - 2mz=2 ws(m) against the length of s-sequences d are s h o w n in Fig. 12.
T h e experimentally determined values
of the associated fraction p are indicated b y arrows and horizontal dashed lines in these plots.
The corresponding intercepts on the horizontal axis
indicate the value (q -1), w h e r e q is the sequences
(cf. Eq. 8).
m i n i m u m length of associated
Fig. 12 exhibits good agreement, indicating that the
m i n i m u m length of aggregated s-sequences for s - P M M A
self-aggregation in
toluene (and similarly in o-dichlorobenzene a n d BAC) is equal to 9 m o n o m e r units (ref. 54,111).
.~ 1"0I N~ ,
0.8
0.6
0.40,2O15 20 d (in monomer units}
10
d
Fig. 12. D e p e n d e n c e of the value fs(1) - ~=_z2 ws(m) on the s-sequence length d for s - P M M A - I (S -- 89.5%; H = 8.5%) (o);-s-PMMA-2 (S -- 85%; H = 12%)) (e); s - P M M A - 3 (S = 66%; H -- 31%) (A). T h e experimentally found values of associated fraction p for toluene-d 8 solutions of s - P M M A are indicated b y arrows a n d dashed horizontal lines (ref. 111).
ll9 C o n t r a r y to t h e m e n t i o n e d s o l v e n t s , in CC14 (which is a v e r y p o o r s o l v e n t f o r PMMA), a p p r e c i a b l e s e l f - a g g r e g a t i o n t a k e s p l a c e e v e n w i t h s-PMI~IA of low stereoregularity
{s-PMMA-3), a s i n d i c a t e d b y t h e r e s u l t s of NFIR, o s m o m e t r y
and cloud-point curves
( r e f . 3,53,55).
C. T h e r m a l s t a b i l i t y a n d d e c o m p o s i t i o n of a ~ g r e ~ a t e s The d e c o m p o s i t i o n of s t e r e o c o m p l e x a g g r e g a t e s in a c e r t a i n t e m p e r a t u r e r a n g e ( t h e i r " m e l t i n g " ) h a s b e e n p r o v e d b y v a r i o u s m e t h o d s a n d d e s c r i b e d in a n u m b e r of p a p e r s (ref. 1,33,40,42,56,60,64-66,69,74,75,82,83,98,103-105).
In
t h e c i t e d p a p e r s , v a r i o u s t e m p e r a t u r e r a n g e s c o r r e s p o n d i n g to t h e " m e l t i n g " of s t e r e o c o m p l e x a g g r e g a t e s a r e q u o t e d , d u e to t h e c i r c u m s t a n c e t h a t t h e s t a b i l i t y of t h e s t e r e o c o m p l e x s t r o n g l y d e p e n d s on t h e s t e r e o r e g u l a r i t y of t h e i n t e r a c t i n g p o l y m e r s a n d also on s o l v e n t . A l r e a d y in t h e f i r s t p a p e r s on t h e s t e r e o c o m p l e x , it was o b s e r v e d t h a t t h e m e l t i n g p o i n t of t h e gel d e c r e a s e s w i t h t h e d e c r e a s i n g t a c t i c i t y of t h e s - c o m p o n e n t , s i m i l a r l y a s t h e t e m p e r a t u r e s of a g g r e g a t e d e c o m p o s i t i o n d e t e r m i n e d f r o m t u r b i d i m e t r i c m e a s u r e m e n t s ( r e f . 1,33,82,83).
The c h a r a c t e r
of t h e t h e r m a l s t a b i l i t y of s t e r e o c o m p l e x a g g r e g a t e s in d e p e n d e n c e on t h e s t e r e o r e g u l a r i t y of t h e s - c o m p o n e n t was s t u d i e d in g r e a t e r d e t a i l b y NMR s p e c t r o s c o p y ( r e f . 103).
The t e m p e r a t u r e d e p e n d e n c e of t h e a s s o c i a t e d
f r a c t i o n p f o r m i x t u r e s o f i - a n d s-PMMA in b e n z e n e , w i t h v a r i o u s s t e r e o r e g u l a r i t y of t h e s - c o m p o n e n t , is i l l u s t r a t e d in Fig. 13.
At a g i v e n
t e m p e r a t u r e , " m e l t i n g " p r o c e e d s v e r y q u i c k l y u p to a c e r t a i n v a l u e of p which does not f u r t h e r
c h a n g e w i t h time.
From Fig. 13, it c a n b e s e e n t h a t
f o r all s a m p l e s , m e l t i n g b e g i n s a t a p p r o x i m a t e l y t h e same t e m p e r a t u r e (['40"C).
F o r m i x t u r e s w i t h s-PMMA of h i g h e r s t e r e o r e g u l a r i t y , t h e " m e l t i n g "
r a n g e b r o a d e n s and complete dissociation takes place at h i g h e r temperatures.
At t h e same time, t h e s h a p e of t h e t e m p e r a t u r e d e p e n d e n c e
d o e s n o t d e p e n d o n t h e mixing ratio.
A c o m p a r i s o n of t h e t e m p e r a t u r e
d e p e n d e n c e s of p f r o m Fig. 13 w i t h t h e c o r r e s p o n d i n g d e p e n d e n c e s of t h e d q u a n t i t y fs(1) -mZ=2 Ws(m) o n s e q u e n c e l e n g t h d (Fig. I I ) r e v e a l s t h a t t h e y a r e v e r y similar. aggregates
This i n d i c a t e s t h a t t h e d e c o m p o s i t i o n of s t e r e o e o m p l e x
b y h e a t i n g c o r r e s p o n d s to t h e d i s t r i b u t i o n of s e q u e n c e l e n g t h s o f
t h e s - c o m p o n e n t ( t h e i - c o m p o n e n t is almost p e r f e c t ) , while t h e minimum s e q u e n c e l e n g t h n e c e s s a r y f o r a s s o c i a t i o n (q) e x h i b t s a n a l m o s t l i n e a r t e m p e r a t u r e d e p e n d e n c e in a c e r t a i n t e m p e r a t u r e r a n g e .
With some
a p p r o x i m a t i o n , it c a n t h e r e f o r e be s t a t e d t h a t a d e f i n e d " m e l t i n g " t e m p e r a t u r e c o r r e s p o n d s to a c e r t a i n l e n g t h of a s s o c i a t e d s e q u e n c e s .
With m i x t u r e s of i -
a n d s-PMMA in b e n z e n e , t h e l e n g t h e n i n g of t h e s - s e q u e n c e b y o n e monomer u n i t i n c r e a s e s t h e m e l t i n g t e m p e r a t u r e b y ~2"C.
An a p p r e c i a b l e d e v i a t i o n
from a l i n e a r t e m p e r a t u r e d e p e n d e n c e o f t h e minimum l e n g t h q c a n
120
8O
60
40-
20
0
I
I
I
30 F i g 13. T e m p e r a t u r e for various mixtures i-PMMA + s - P M M A - 1 (l:l); ~ , i-PMMA + s - P M M A - 3 (S -- 66%; be observed
I
I
I
70 90 ternperGture, "C
dependence of the fraction p of associated monomer units o f i-PMMA (I -- 97%; H -- 3%) a n d s - P M M A i n b e n z e n e ; o, (S = 88.5%; H = 9%) (1:2); (o), i-PMMA + s - P M M A - I s - P M M A - 2 (S = 69%; H = 27.4%) (1:2); a, i-PMMA + H = 31%) (1:1.5) ( r e f . 103).
at temperatures
decomposition dependence
l
50
(cf. F i g s . l l
of fs(1) - z
approaching and
the temperature
13); t h i s i s q u i t e
ws(m) on the length
of complete
understandable
d approaches
because
the
zero
asymptotically. The character
of the temperature
( r e f . 103) i s s i m i l a r to t h a t and
observed
s-PMMA, the temperature
the used
solvent.
of stereocomplex high upper
range
The upper aggregates
stereoregularity
For a given
of stereocomplex
generated
"melting"
by interaction
lies at temperaturaes
i-PMMA a n d
f r o m NMR s p e c t r a )
of p in other
in benzene.
limit of the temperature
limits of the temperature
stereoregular
dependences
range
around
of "melting"
range
solvents
are
given
of i-
depends
on
of decomposition
of i- and
s-PMMA of
1 2 0 - 1 3 0 " C ( F i g . 8). for mixtures
s-PMMA of lower stereoregularity
for various
solvents mixture
The
of highly
(as determined
in Table 4 in Part
V-E.
It
can be seen that stereocomplex aggregates are most stable in CC14 a n d in toluene; the high thermal stability of the stereocomplex in toluene w a s also revealed b y m e a s u r e m e n t s of gel melting points (ref. 67,74). The finding that associated segments containing long s-sequences "melt" at higher temperatures than segments formed b y short s-sequences and a certain similarity of the described association with crystallization imply that the binding Gibbs e n e r g y (per tool of m o n o m e r
units) will be higher for
121 TABLE 4 Values of the fraction sequences
of associated
units,
of the minimum length
q (both at 25°C) and of the temperature
of stereocomplex of solubility
aggregates
parameters
3%; S : 0} a n d
Tm in different
5; v a l u e s
of complete
solvents
of p for mixtures
of dipole moments p and o f i-PMMA (I : 97%; H =
s - P M M A (I : 3%; H : 31%; S : 66%), w e i g h t
( d a t a f r o m r e f . 103 a n d
Solvent
unpublished
p
ratio i/s
p
(cal cm-3) I/2
q
T m
(%)
('C)
CC14
0
8.6
95
3
95 a
acetonitrile
3.4
11.9
95
3
70
DMF
3.8
12.1
90
3
_b
toluene
0.37
8.9
80
4-5
85
o-dichlorobenzene
2.5
10.0
38
9-10
70
benzene
0
9.2
35-40
8-10
60
benzaldehyde
2.8
9.4
25
12-13
60
chloroform
1.05
9.3
0
-
-
aEstimated to 75"C
from the course
= 1/2
data).
6
(debye)
of associated decomposition
of the temperature
dependence
of p measured
up
bNot measured
associated
segments
stereoregularity predominate heats
formed
by long s-sequences
of the i-component
in s-PMMA of high
is assumed)
stereocomplex
formation
depends
for higher
( r e f . 103).
stereoregularity.
o f m i x i n g , B i r o ~ e t al. h a v e a c t u a l l y
strongly
(a p r a c t i c a l l y
Long sequences
From measurements
proved
i n DMF c o r r e s p o n d i n g
on the stereoregularity
perfect
( r e f . 93) t h a t
to t h e s t o i c h i o m e t r i c
of the s-component
of the
the heat of
and
ratio
(i/s)
is higher
stereoregularity.
The temperature
dependence
of the fraction
p of associated
units
characterizing the thermal stability of i- and s - P M M A self-aggregates in o-dichlorobenzene (ref. 2,3,102) is demonstrated in Fig. 14.
The dependences
of the fraction p in toluene had a perfectly similar character and their concentration independence in the range 0.2-10% was likewise observed (ref. 54,109,110). Fig. 14 demonstrates the completely different thermal stability of the i- and
s-PMMA self-aggregates.
self-aggregates very results
stable
and
While the fraction
at room temperature they
of osmometry,
decompose viscometry,
is very
completely
p of s-PMMA
high, these
aggregates
at 60"C, in agreement
light scattering
and
are not with the
IR s p e c t r o s c o p y
(ref.
122
80 d.
60 s-PMMA 40
-
20 i-PMMA i~,
0
50
I
100
I
\ \
150 200 temperQture,°C
Fig. 14. T e m p e r a t u r e d e p e n d e n c e of t h e f r a c t i o n of a s s o c i a t e d monomer u n i t s p f o r s o l u t i o n s of i-PMMA ( ) a n d s-PMMA ( - - - ) in o - d i c h l o r o b e n z e n e ( r e f . 3,102).
47,54,102).
The amount of i-PMMA s e l f - a g g r e g a t e s at room temperature is
relatively small, but these a g g r e g a t e s exhibit a high thermal stability; temperatures above 160°C, comparable with the melting temperature of solid i-PMMA, are n e c e s s a r y for their complete decomposition. While for solutions of i-PMMA in toluene-d8 only a small content of a g g r e g a t e s (p = 10%) was observed even at -60"C and this content did not change in the r a n g e -60 to 110"C (ref. 119), for solutions of i-PMMA in BAC a
s h a r p i n c r e a s e of t h e a g g r e g a t e d f r a c t i o n p t a k e s p l a c e a t t e m p e r a t u r e s below 0"C, w i t h m a c r o s c o p i c s e p a r a t i o n of most of i-PMMA f r o m t h e s o l u t i o n ( r e f . 47).
Also, most of t h e s-PMMA is a g g r e g a t e d
c a s e , h o w e v e r , a t t e m p e r a t u r e s below 60"C.
( s e p a r a t e d ) in BAC; in t h i s
It is i n t e r e s t i n g t h a t b o t h i - a n d
s-PMMA s e p a r a t e from BAC s o l u t i o n a t t e m p e r a t u r e s a b o v e t h e o t e m p e r a t u r e of at-PMMA (-20"C). A c o m p a r i s o n of F i g s . 8,13 a n d 14 i n d i c a t e s t h a t t h e t h e r m a l s t a b i l i t y of s t e r e o c o m p l e x a g g r e g a t e s f o r m e d b y i n t e r a c t i o n of i - a n d s-PMMA of h i g h s t e r e o r e g u l a r i t y is c o n s i d e r a b l y h i g h e r t h a n t h e t h e r m a l s t a b i l i t y of t h e s e l f - a g g r e g a t e s of h i g h l y s t e r e o r e g u l a r s-PMMA.
Together with the finding
t h a t b y c o o l i n g of a m i x t u r e of t o l u e n e s o l u t i o n s of i - a n d s-PMMA f r o m 130" to 25"C no s e l f - a g g r e g a t e s a r e f o r m e d , b u t t h e s t e r e o c o m p l e x is g e n e r a t e d , t h i s i n d i c a t e s t h a t t h e i n t e r a c t i o n s of t h e s t e r e o c o m p l e x t y p e a r e s t r o n g e r t h a n t h e i n t e r a c t i o n s l e a d i n g to s-PMMA s e l f - a g g r e g a t i o n ( r e f . 22).
123 D. K i n e t i c s of a g g r e g a t i o n a n d e f f e c t of t h e r m a l h i s t o r y The time c o u r s e of PMMA s t e r e o c o m p l e x f o r m a t i o n w a s followed b y v a r i o u s m e t h o d s b o t h f o r d i l u t e s o l u t i o n s a n d f o r g e l s of c o n c e n t r a t e d s o l u t i o n s . V i s c o m e t r i c m e a s u r e m e n t s h a v e s h o w n t h a t t h e c h a n g e s of v i s c o s i t y w i t h time (i.e., i t s d e c r e a s e o r g r o w t h , in d e p e n d e n c e on s o l v e n t - - s e e P a r t IV-A, V i s c o m e t r y ) is t h e s h a r p e r , t h e h i g h e r t h e c o n c e n t r a t i o n of t h e s o l u t i o n (ref. 44,67).
M e a s u r e m e n t s of l i g h t s c a t t e r i n g h a v e y i e l d e d t h e time d e p e n d e n c e s
of /~/wapp a n d of t h e g y r a t i o n r a d i u s Rg f o r s t e r e o c o m p l e x a g g r e g a t e s in DMF ( r e f . 43).
While Flwapp i n c r e a s e s s h a r p l y a l r e a d y d u r i n g t h e f i r s t m i n u t e s ,
Rg r e m a i n s c o n s t a n t f o r a r e l a t i v e l y l o n g time a n d i t s i n c r e a s e is o b s e r v e d o n l y a f t e r a v e r y l o n g time (~ d a y ) .
A similar c h a r a c t e r of t h e time
d e p e n d e n c e s of Mwp p a n d Rg was also o b s e r v e d b y B e l n i k e v i t c h e t al. ( r e f . 44), who h a v e a l s o o b s e r v e d t h a t t h e s t e r e o c o m p l e x is f o r m e d more q u i c k l y in DMF t h a n in d i o x a n e .
The o b s e r v a t i o n t h a t t h e size of t h e s t e r e o e o m p l e x
a g g r e g a t e s d o e s n o t c h a n g e f o r a r e l a t i v e l y l o n g time while t h e i r m a s s i n c r e a s e s i n d i c a t e s a g r o w t h of t h e d e n s i t y of a g g r e g a t e d monomer u n i t s (i.e., the aggregates
g r o w more c o m p a c t w i t h time).
The i n c r e a s e of Rg a f t e r a
l o n g time is e x p l a i n e d b y t h e p r o c e s s of s e c o n d a r y a g g r e g a t i o n of s t e r e o c o m p l e x p a r t i c l e s a n d f o r m a t i o n of l a r g e r s t r u c t u r e s .
Such a secondary
p r o c e s s is a l s o i n d i c a t e d b y t h e r e s u l t s of v i s c o m e t r i c a n d DSC m e a s u r e m e n t s ( r e f . 51,74,96). NMR m e a s u r e m e n t s h a v e s h o w n t h a t w i t h m i x t u r e s of i - a n d s-PMMA in CD3CN o r CC14 ( c o n c e n t r a t i o n 10%) a t room t e m p e r a t u r e t h e p r o c e s s of s t e r e o c o m p l e x f o r m a t i o n is so r a p i d t h a t it c a n n o t be followed b y t h i s technique.
I n b e n z e n e , o - d i c h l o r o b e n z e n e a n d b e n z a l d e h y d e , a s s o c i a t i o n is
r a p i d o n l y a t t h e b e g i n n i n g , w h e n a v e r y q u i c k e s t a b l i s h m e n t of a c e r t a i n v a l u e of t h e a g g r e g a t e d f r a c t i o n p is o b s e r v e d ; f u r t h e r a s s o c i a t i o n is a v e r y slow p r o c e s s a n d t h e e q u i l i b r i u m s t a t e is r e a c h e d a f t e r a v e r y l o n g time ( r e f . 103).
At t h e same time, t h e r e l a t i v e n u m b e r of u n i t s t a k i n g p a r t in t h i s slow
p r o c e s s i n c r e a s e s with the d e c r e a s i n g s t e r e o r e g u l a r i t y of the s - c o m p o n e n t . T h i s i n d i c a t e s v e r y r a p i d a s s o c i a t i o n o f l o n g s - s e q u e n c e s a n d slow a s s o c i a t i o n of s h o r t s - s e q u e n c e s c o n n e c t e d p r o b a b l y w i t h some r e a r r a n g e m e n t of t h e already generated structure.
P y r l i k a n d R e h a g e ( r e f . 88,91) h a v e m e a s u r e d
t h e time d e p e n d e n c e s of t h e c o m p o n e n t s o f t h e s h e a r m o d u l u s f o r s t e r e o c o m p l e x g e l s in o - x y l e n e .
T h e y o b s e r v e d t h a t t h e e q u i l i b r i u m v a l u e s of
G' i n c r e a s e w i t h d e c r e a s i n g t e m p e r a t u r e ; t h i s t h e y e x p l a i n b y p r o c e e d i n g c r y s t a l l i z a t i o n w i t h d e c r e a s i n g t e m p e r a t u r e a n d t h u s a g r o w i n g d e g r e e of crosslinking (the crystallites act as crosslink points).
The r e a s o n f o r
p r o c e e d i n g c r y s t a l l i z a t i o n a t d e c r e a s i n g t e m p e r a t u r e is s e e n in t h e t e m p e r a t u r e d e p e n d e n c e of t h e minimum l e n g t h of s t e r e o r e g u l a r s - s e q u e n c e s n e c s s a r y f o r c r y s t a l l i z a t i o n , in a g r e e m e n t w i t h t h e r e s u l t s o f NMR
124 spectroscopy
(see p r e c e d i n g
paragraph).
T h e k i n e t i c s of s e l f - a g g r e g a t i o n
of s-PMMA i n t o l u e n e a n d BAC w a s
followed b y a c o m b i n a t i o n of NMR s p e c t r o s c o p y , light scattering
and turbidimetry
r a t e of s-PMMA s e l f - a g g r e g a t i o n
IR s p e c t r o s c o p y ,
( r e f . 38,47,54,111).
viscometry,
It w a s p r o v e d t h a t t h e
increases with decreasing temperature
and
with increasing concentration, with the solvent playing an important part.
At
t h e s a m e time, v a r i o u s m e t h o d s e x h i b i t v a r i o u s s e n s i t i v i t y to d i f f e r e n t p h a s e s of t h e a g g r e g a t i o n t h e time d e p e n d e n c e
process.
T h e s i t u a t i o n is i l l u s t r a t e d in Fig. 15, e x h i b i t i n g
of t h e f r a c t i o n of a g g r e g a t e d
NMR s p e c t r a a n d t h e time d e p e n d e n c e i d e n t i c a l s a m p l e of s-PMMA s o l u t i o n i n
units p determined from
of t h e t u r b i d i t y BAC.
t h a t while the f r a c t i o n p i n c r e a s e s from t h e v e r y turbidity
b e g i n n i n g , a g r o w t h of
o n l y t a k e s p l a c e a t a time w h e n t h e f r a c t i o n p a l m o s t d o e s n o t
c h a n g e a n y more.
Similarly as with the stereocomplex a g g r e g a t e s ,
p r i m a r y a n d a s e c o n d a r y p r o c e s s c a n be a s s u m e d . process
~- m e a s u r e d w i t h a n
Fig. 15 c l e a r l y d e m o n s t r a t e s
also here a
During the primary
( b e s i d e s NMR s p e c t r o s c o p y , t h i s i s a l s o d e t e c t e d b y IR s p e c t r o s c o p y ) ,
"intramolecular" ordering s-sequences
t a k e s p l a c e i n c o n s e q u e n c e of i n t e r a c t i o n s of
(the term "intramolecular" here also includes, for example,
d o u b l e - c h a i n i n t e r a c t i o n s ) a n d c r y s t a l l i t e - l i k e domains are formed (the so c a l l e d " g l o b u l a t i o n " s t a g e a c c o r d i n g to r e f . 38). certain temperature decreasing
At t h e s a m e time, in a
r a n g e , t h e e q u i l i b r i u m v a l u e s of p i n c r e a s e w i t h
temperature
of a g g r e g a t i o n
(Fig. 10); s i m i l a r l y a s in t h e c a s e of
the stereoeomplex, t h i s can be explained b y the d e c r e a s i n g s-sequences
necessary
for the interaction energy
e n e r g y of m o l e c u l a r m o t i o n a t d e c r e a s i n g t e m p e r a t u r e . the "globules" further
aggregate
m i n i m u m l e n g t h of
to e x c e e d t h e t h e r m a l With p r o c e e d i n g time,
(secondary process) under
f o r m a t i o n of
l a r g e r p a r t i c l e s , c a u s i n g , f o r e x a m p l e , t h e s h a r p i n c r e a s e of t u r b i d i t y (flocculation stage).
I
I
50
100
--IT
p
/ "t, min
150
Fig. 15. Correlation of (I) p - t and (2) ~-t c u r v e s for s-PMMA (S = 91.5%; H "7.5%) in BAC (cone. 9x10-3g cm-3) at 48"C; p is the fraction of immobilized monomer u n i t s determined by NMR, ~- is the t u r b i d i t y and t is the aggregation time (rain); p an ~" are expressed in a r b i t r a r y u n i t s (ref. 38).
125 T h e circumstance that for the stereocomplex aggregates in some solvents a v e r y long time is needed for the attainment of the equilibrium state leads to a different course of various quantities during heating and cooling. hysteresis curves for the P M M A
Such
stereocomplex have been observed in
viscosity (ref. 64), dielectric (ref. 52), dynamicomechanical
(ref. 91} a n d N M R
spectroscopic mesurements; the latter have also s h o w n that the stereocomplex in a solution which has not reached the equilibrium state at repeated heating e x h i b i t s a d i f f e r e n t b e h a v i o r ( t h e r a n g e of " m e l t i n g " c o r r e s p o n d i n g segments with short s-sequences spectroscopy,
it w a s f u r t h e r
i s m i s s i n g } ( r e f . 103}.
to
By NMR
s h o w n t h a t t h e a t t a i n m e n t of e q u i l i b r i u m v a l u e s
of p w h i c h f o r m i x t u r e s of i - a n d s-PMMA in b e n z e n e t a k e s a v e r y l o n g time at room t e m p e r a t u r e if a g g r e g a t i o n
( w e e k s to m o n t h s } c a n b e r e c h e d a l m o s t i n s t a n t a n e o u s l y
takes place at -70"C or even lower temperatures.
This is
p r o b a b l y a c o n s e q u e n c e of t h e c i r c u m s t a n c e t h a t t h e r a t e of a g g r e g a t i o n increases with decreasing aggregation
temperature
s o t h a t a t low t e m p e r a t u r e s
is p r o b a b l y e v e n m o r e r a p i d t h a n t h e p r o c e s s of s o l v e n t
solidification.
T h e time e f f e c t a l s o h a s to b e c o n s i d e r e d i n c o m p a r i s o n s of
v a r i o u s s t u d i e s of s-PMMA s e l f - a g g r e g a t i o n
{ref. 38,47,54}.
H o w e v e r , b o t h w i t h t h e s t e r e o c o m p l e x a n d w i t h s-PMMA s e l f - a g g r e g a t e s , e f f e c t s of t h e r m a l h i s t o r y h a v e b e e n o b s e r v e d than the above described
which have a different origin
k i n e t i c s of a g g r e g a t i o n .
In d y n a m i c a l - m e c h a n i c a l
m e a s u r e m e n t s , P y r l i k e t al. ( r e f . 88,89) h a v e o b s e r v e d
t h a t if t h e m i x t u r e of
i - a n d s-PMMA i n o - x y l e n e w a s h e a t e d to 120"C (i.e., o n l y a b o u t 10"C a b o v e t h e m e l t i n g p o i n t of t h e gel}, t h e n a f t e r c o o l i n g to 80"C g e l f o r m a t i o n p r o c e e d s m u c h m o r e r a p i d l y t h a n a f t e r p r e v i o u s h e a t i n g to 145"C.
From
t u r b i d i m e t r i c m e a s u r e m e n t s , a s i m i l a r e f f e c t of t h e r m a l h i s t o r y w a s o b s e r v e d also for aggregation
in d i l u t e s o l u t i o n s of s-PMMA in BAC ( r e f . 38}.
In both
c a s e s , t h i s b e h a v i o r is e x p l a i n e d b y t h e e x i s t e n c e o f s t a b l e n u c l e i w h i c h a r e a b l e to s u r v i v e f o r s o m e time a t t e m p e r a t u r e s "melting".
even above the upper
limit of
N u c l e a t i o n m e c h a n i s m s a r e a l s o u s e d to e x p l a i n t h e o b s e r v a t i o n
that the mechanical properties temperatures
of s t e r e o c o m p l e x g e l s g e n e r a t e d
differ considerably at a given temperature
c o m p a r i s o n of the r e s u l t s o b t a i n e d by light s c a t t e r i n g o s m o m e t r y , v i s c o m e t r y a n d NMR s p e c t r o s c o p y
at various
( r e f . 88,89).
A
w i t h t h e r e s u l t s of
i n d i c a t e s t h a t the f r a c t i o n of
s u c h n u c l e i i n s o l u t i o n s of s-PMMA in BAC m u s t be v e r y small {ref. 38}. this system, another spectroscopy
distinct "hysteretie"
when aggregates
( p r e c i p i t a t e } f o r m e d a t 25"C w e r e h e a t e d .
16 s h o w s t h a t t h e g i v e n " e q u i l i b r i u m " v a l u e of p r e a c h e d d u r i n g at a higher temperature
In
e f f e c t w a s f o u n d b y NMR
than the aggregation
temperature
Fig.
h e a t i n g lies
needed for
r e a c h i n g t h e s a m e " e q u i l i b r i u m " v a l u e of p ( d u r i n g t h e a g g r e g a t i o n process}.
This i n d i c a t e s t h a t some s t r u c t u r a l
rearrangements
s e e m to o c c u r
126
100 --', 80
""
~,
60 40!
2bl I1Q
20
40 60 80 ternperat ure,'C
Fig. 16. D e p e n d e n c e of t h e " e q u i l i b r i u m " v a l u e s of f r a c t i o n p ( a g g r e g a t e d m o n o m e r u n i t s ) o n t e m p e r a t u r e of s-PMMA iS = 91.5%; H - 7.5%; c o n c . 9.0 x 1 0 - 3 g c m -3) i n BAC ( l a ) a n d t o l u e n e - d 8 (2a), c o m p a r e d w i t h t h e t e m p e r a t u r e d e p e n d e n c e of f r a c t i o n p d u r i n g t h e h e a t i n g of a g g r e g a t e s f o r m e d a t 25"C ( c u r v e s l b a n d 2b) ( r e f . 38).
a l s o in t h e p r e c i p i t a t e ; t h e s y s t e m t e n d s to h i g h e r s t a b i l i t y a l s o d u r i n g a g e i n g of t h e p r e c i p i t a t e .
E. E f f e c t of s o l v e n t o n t h e f o r m a t i o n of a g g r e g a t e s The original papers
d e s c r i b e s t e r e o c o m p l e x formation only in polar
s o l v e n t s like DMF o r a c e t o n i t r i l e ( r e f . 1,33} b u t Liu a n d Liu {ref. 65} w e r e t h e f i r s t to o b s e r v e benzene or toluene.
s t e r e o c o m p l e x f o r m a t i o n a l s o i n n o n p o l a r s o l v e n t s like Solid s t e r e o c o m p l e x s a m p l e s i s o l a t e d f r o m a c e t o n e ,
acetonitrile or benzene solution exhibit the same X-ray pattern
( r e f . 69).
T h e e f f e c t o f s o l v e n t o n s t e r e o c o m p l e x f o r m a t i o n c a n be c o m p a r e d q u a n t i t a t i v e l y f r o m t h e r e s u l t s of NMR s p e c t r o s c o p y characterizing i n T a b l e 4.
( r e f . 103).
Data
s t e r e o c o m p l e x f o r m a t i o n i n a s e r i e s of s o l v e n t s a r e s u m m a r i z e d
V a l u e s of p f o r m i x t u r e s w i t h t h e s - c o m p o n e n t of l o w e r
stereoregularity
are cited intentionally.
high stereoregularity,
t h e v a l u e s of p a r e m u c h l e s s s e n s i t i v e to t h e n a t u r e
of t h e s o l v e n t (p = 85 - 100%}. corresponding
F o r m i x t u r e s of i - w i t h s-PMMA of
T h e s a m e i s t r u e of t h e t e m p e r a t u r e
values
to c o m p l e t e d e c o m p o s i t i o n , Tin, w h i c h o f t e n lie a b o v e t h e
b o i l i n g p o i n t o f t h e s o l v e n t w i t h s - c o m p o n e n t s of v e r y h i g h s t e r e o r e g u l a r i t y . F r o m T a b l e 4, it i s e v i d e n t t h a t t h e e x t e n t of s t e r e o c o m p l e x f o r m a t i o n i s n o t d e t e r m i n e d b y t h e p o l a r i t y of t h e s o l v e n t .
P r a c t i c a l l y all m o n o m e r i c u n i t s
a r e a s s o c i a t e d b o t h i n t h e h i g h l y p o l a r a e e t o n i t r i l e o r DMF a n d in n o n p o l a r CCI4.
Lower p values are observed
benzaldehyde)
in b o t h polar ( o - d i c h l o r o b e n z e n e ,
and nonpolar (benzene} aromatic solvents.
Neither can the
medium e f f e c t s u p o n s t e r e o c o m p l e x formation be c o r r e l a t e d with the solubility parameter
~ ( s q u a r e r o o t of t h e c o h e s i o n e n e r g y
association has been observed
density} alone.
No
i n c h l o r o f o r m , e v e n f o r m i x t u r e of i-PMMA w i t h
127 s-PMMA of h i g h s t e r e o r e g u l a r i t y
a t low t e m p e r a t u r e
(-50"C).
S o l v e n t s in
w h i c h s t e r e c o m p l e x f o r m a t i o n t a k e s p l a c e c a n b e c l a s s i f i e d a c c o r d i n g to t h e m i n i m u m l e n g t h of a s s o c i a t e d s - s e q u e n c e s ,
q.
In agreement with the
t e r m i n o l o g y i n t r o d u c e d o r i g i n a l l y b y C h a l l a e t al. (ref. 35), t h e s o l v e n t s w i t h q ~ 3 m a y be r e g a r d e d
a s s t r o n g l y c o m p l e x i n g , t h e s o l v e n t s w i t h q ~ 10 a s
weakly complexing and chloroform as non-complexing.
T h i s c l a s s i f i c a t i o n is
a l s o in a g r e e m e n t w i t h t h e c l a s s i f i c a t i o n g i v e n in r e f . 37, a n d it is s u m m a r i z e d i n T a b l e 5~ w h e r e s o m e f u r t h e r
solvents are also included.
Some
d i s c r e p a n c i e s exist c o n c e r n i n g the clas s ificatio n of toluene; c o n s i d e r i n g the v a l u e s of t h e m i n i m u m l e n g t h q, t h i s s o l v e n t is c l a s s i f i e d a s s t r o n g l y c o m p l e x i n g a n d t h i s is s u p p o r t e d
b y t h e r e l a t i v e l y h i g h t h e r m a l s t a b i l i t y of
t h e s t e r e o c o m p l e x i n t h i s s o l v e n t {Table 4 a n d r e f . 67,74).
On t h e o t h e r
h a n d , t h e v i s c o m e t r i c b e h a v i o r (ref. 35) a n d e s p e c i a l l y t h e c a l o r i m e t r i c a l l y d e t e r m i n e d v a l u e s of t h e h e a t of f o r m a t i o n of t h e s t e r e o c o m p l e x ( r e f . 93) classify toluene as weakly complexing.
The tendency
to s t e r e o c o m p l e x
f o r m a t i o n is v e r y w e a k i n c h l o r o b e n z e n e (ref. 44,65,77).
T h e s t e r e o c o m p l e x is
a l s o f o r m e d in s o m e o t h e r s o l v e n t s like o - x y l e n e ( r e f . 67,88), t r i m e t h y l b e n z e n e ( r e f . 67), m e t h y l a c e t a t e r e f . 58), e t h y l a c e t a t e a n d BAC ( r e f . 45,71).
TABLE 5 C l a s s i f i c a t i o n of s o l v e n t s a c c o r d i n g to t h e i r t e n d e n c y to s t i m u l a t e PMMA s t e r e o c o m p l e x f o r m a t i o n ( r e f . 35,37,103) Strongly complexing
Weakly complexing Non-complexing
CC14
DMSO
benzene
chloroform
acetonitrile
methyl isobutyrate
o-dichlorobenzene
dichloromethane
DMF
THF
benzaldehyde
acetone
MMA
dioxane thiophene ? ~- t o l u e n e -~ ?
T h e v a l u e s of t h e a g g r e g a t e d
? ~- c h l o r o b e n z e n e -~ ?
f r a c t i o n p, c h a r a c t e r i z i n g
self-aggregation
i-PMMA a n d s-PMIVIA i n v a r i o u s s o l v e n t s , a r e s u m m a r i z e d in T a b l e 6.
of
From
t h i s t a b l e , it c a n be s e e n t h a t t h e v a l u e s of p f o r i-PMMA a r e n o t v e r y h i g h a n d t h a t t h e y show little d e p e n d e n c e on s o l v e n t ( p e r h a p s with t h e exception of chloroform).
S e l f - a g g r e g a t i o n o f s-PMMA w a s m o s t l y o b s e r v e d
p o l y m e r of h i g h s t e r e o r e g u l a r i t y .
only for the
An e x c e p t i o n i s CC14, w h e r e a g g r e g a t i o n
e v e n of c o n v e n t i o n a l PMMA i s a p p r e c i a b l e .
H o w e v e r , f r o m a c o m p a r i s o n of
T a b l e s 5 a n d 6, it c a n be s e e n t h a t t h e e f f e c t of s o l v e n t o n s t e r e o c o m p l e x
128 TABLE 6 V a l u e s of t h e f r a c t i o n of a s s o c i a t e d u n i t s p (at 25"C) f o r i-PMMA a n d s-PMMA of v a r i o u s s t e r e o r e g u l a r i t y
in v a r i o u s s o l v e n t s {data f r o m r e f .
2,3,38,47,54,102,109,110)
Solvent
i-PMMA
s-PMMA-1
s-PMMA-2
(I:97% H:3% S : 0 ) (I:2.5% H:9% S:88.5%) (I:3.5% H:31.5% S:65%)
CC14
20-24
-~100a
40-48
toluene
10
85
0
o-dichlorobenzene
15
70-85
0
butylacetate
_b
90
0
DMF
17
18
0
acetonitrile
18-23
0-5
_b
benzene
12-15
5
0-4
chloroform
0-12
0
0
as-PMMA-1 could not be dissolved in CCI4 bnot measured
formation and on self-aggregation of s-PMMA is not parallel and this is most evident for acetonitrile.
Using a terminology analogous to that used for the
stereocomplex, then CCI4, butyl acetate, toluene, o-dichlorobenzene can be classified as strongly promoting self-aggregation whereas in acetonitrile, benzene and chloroform self-aggregation of s-PMMA practically does not take place, which is in agreement with the results of IR spectroscopy, osmometry and viscometry (ref. 22,54,102).
IR spectroscopy and X-ray diffraction
indicate that ordering of s-PMMA also takes place in 1,2-dichloroethane (ref. 115) and in diethyl ketone and chloroacetone (ref. 22,100,101). Aggregation of conventional PMMAis cited in p-xylene and in butyl chloride (ref. 53,55). T h e f o r m a t i o n of t h e PMMA s t e r e o c o m p l e x w a s a l s o s t u d i e d i n m i x e d solvents.
Sedimentation measurements have shown that the stereocomplex
e x i s t s i n m i x t u r e s of D M F / b e n z e n e a n d t h a t t h e s t e r e o c o m p l e x f r a c t i o n i n c r e a s e s w i t h i n c r e a s i n g c o n t e n t of DMF ( r e f . 48), w h i c h i s i n a g r e e m e n t w i t h t h e r e s u l t s of NMR s p e c t r o s c o p y
(cf. T a b l e 4).
T h e k i n e t i c s of
stereoeomplex formation was studied by light scattering
i n a m i x t u r e of
DMF/CC14and it w a s f o u n d t h a t e v e r y time t h e s t e r e o c o m p l e x a g g r e g a t e s t h i s m i x t u r e a r e l i g h t e r a n d s m a l l e r t h a n i n DMF a l o n e ( r e f . 45).
in
The results
of t h e m e a s u r e m e n t of p o l a r i z e d l u m i n e s c e n c e h a v e s h o w n t h a t i n d i l u t e s o l u t i o n s i n a m i x t u r e of D M F / c h l o r o f o r m , s t e r e o c o m p l e x d e c o m p o s i t i o n t a k e s p l a c e i n a n a r r o w r a n g e of s o l v e n t c o m p o s i t i o n (35-50 v o l t of c h l o r o f o r m ) ,
129 confirming the cooperative character s t e r e o c o m p l e x ( r e f . 58}.
of t h e i n t e r m o l e c u l a r b o n d s in t h e
B a s e d o n v i s c o m e t r i c a n d NMR m e a s u r e m e n t s , Liu a n d
Liu {ref. 65) f o u n d t h a t t h e s t e r e o c o m p l e x is n o t f o r m e d in a c e r t a i n c o m p o s i t i o n r a n g e of a m i x t u r e of a c e t o n i t r i l e / b e n z e n e ,
in s p i t e of t h e f a c t
t h a t it is f o r m e d i n t h e s i n g l e c o m p o n e n t s of t h i s mixed s o l v e n t . behavior was observed
A similar
b y Katime e t al. ( r e f . 51) f o r t h e s t e r e o c o m l e x in a
m i x t u r e of a c e t o n i t r i l e / C C 1 4 a n d a c e t o n i t r i l e / b u t y l c h l o r i d e strongly complexing solvents} and for aggregates m i x t u r e of C C 1 4 / b u t y l c h l o r i d e {ref. 55}.
(i.e, f o r m i x t u r e s of
of c o n v e n t i o n a l PMMA in a
The authors
interpret
t h i s e f f e c t in
t e r m s of e x c e s s G i b b s e n e r g y , w h e r e i n c o m p a t i b i l i t y o f t h e c o m p o n e n t s o f t h e c o s o l v e n t m i x t u r e l e a d s to p r e f e r e n c e to " d i s s o l u t i o n " of PMMA a g g r e g a t e s
of t h e p o l y m e r - s o l v e n t i n t e r a c t i o n a n d (ref. 51,55,122).
H o w e v e r , it s h o u l d be
n o t e d t h a t o u r p r e l i m i n a r y r e s u l t s o b t a i n e d b y m e a n s of NMR a n d IR spectroscopy
do n o t i n d i c a t e d e c o m p o s i t i o n of t h e p r i m a r y o r d e r of t h e
s t e r e o c o m p l e x i n c o s o l v e n t m i x t u r e s ( r e f . 123}. only the secondary hindered
process
We h o l d a s m o r e p r o b a b l e t h a t
{i.e., a g g r e g a t i o n of s t e r e o c o m p l e x p a r t i c l e s } i s
in c o s o l v e n t m i x t u r e s a n d t h i s i s a l s o in a g r e e m e n t w i t h t h e r e s u l t s
of DSC a n a l y s i s {ref. 96}. The e x p l a n a t i o n of the m e c h a n i s m b y which v a r i o u s s o l v e n t s promote or h i n d e r e t e r e o a s s o c l a t i o n in n o t q u i t e c l e a r s o f a r . aggregation
Some a u t h o r s
explain
of PMMA b y t h e t e n d e n c y of s o m e p o l a r s o l v e n t s {e.g.,
a c e t o n i t r i l e ) to s e l f - a s s o c i a t e ( l i q u i d o r d e r ) , w h i c h h i n d e r s w i t h t h e p o l y m e r ( r e f . 51,55,122}.
their interaction
However, s u c h a " p a s s i v e " role of the
s o l v e n t d o e s n o t e x p l a i n t h e c o m p l e t e l y d i f f e r e n t e f f e c t o f a c e t o n i t r i l e in s t e r e o c o m p l e x f o r m a t i o n a n d in s e l f - a g g r e g a t i o n
of s-PMMA.
On t h e o t h e r
h a n d , t h e r e e x i s t s t u d i e s a s s u m i n g a n " a c t i v e " r o l e of t h e s o l v e n t e v e n f o r ordering
o f s-PMMA i n t h e s o l i d s t a t e ( r e f . 24,100,101}.
In our opinion, the solvent can affect aggregation
of PMMA b y two
m e c h a n i s m s (ref. 22): 1} c h a n g e s of t h e c o n f o r m a t i o n a l s t r u c t u r e stereoregular
sequences
(conformer energy
of
d i f f e r e n c e s t h e n also become
i m p o r t a n t } w i t h p r o m o t i o n o r h i n d r a n c e of s t e r i c a l l y c o m p l e m e n t a r y i n t e r a c t i o n s ; a n d 2) h i n d r a n c e
(or p r o m o t i o n } of s t e r e o a s s o c i a t i o n b y s p e c i f i c
interactions with certain functional groups.
Concerning the first mechanism,
the e f f e c t of s o l v e n t on the conformational s t r u c t u r e has actually been observed
( e s p e c i a l l y o f s-PMMA}
f r o m 13C a n d 1H NMR r e l a x a t i o n m e a s u r e m e n t s a n d
b y m e a n s o f NMR s h i f t r e a g e n t s
( r e f . 29,124).
The e f f e c t of s o l v e n t on t h e
c o n f o r m a t i o n a l e q u i l i b r i u m o f s-PMMA i n s o l u t i o n i s i n d i c a t e d b y t h e r e s u l t s of IR s p e c t r o s c o p y
( r e f . 21,22,29}.
i n t e r a c t i o n s o f PMMA e s t e r g r o u p s
For the second mechanism, specific (these groups
are i m p o r t a n t in
s t e r e o a s e o c i a t i o n o f PMMA; s e e l a t e r o n i n t h e f o l l o w i n g p a r t } w i t h b e n z e n e molecules have been described
in t h e l i t e r a t u r e
( r e f . 125,126}.
The
130 experimental formed,
finding
that
in benzene
while the stereocomplex
interactions
of stereocomplex
unfavorable
effect of solvent,
self-aggregates
(cf. P a r t
circumstance
that
formation
takes
hydrogen
bonds
proved
Rehage
are
sufficient
while the weaker
neither
self-aggregation
place in chloroform between
between
chloroform
at-PMMA.
of stereoregular
LOCAL
STRUCTURE
A. C h a r a c t e r
to c o m p e n s a t e
for the
of s-PMMA
for this end.
Similarly, the
with the existence
carbonyls
which
have
of been
I n t h e s a m e w a y {i.e., b y c o m p l e x PMMA e s t e r
clarification
OF AGGREGATED
groups},
on association
Kock and of cross-linked
of the effect of solvent
PMMA d e s e r v e s
of the interactions
the stronger
of s-PMMA nor stereoeomplex
molecules and
However, a complete
so that
interactions
molecules and
( r e f . 127}.
solvent
of s-PMMA are not
could be connected
( r e f . 63) e x p l a i n t h e e f f e c t o f s o l v e n t
aggregation
VI.
type
V-C) a r e i n s u f f i c i e n t
in small molecules
formation
self-aggregates
is, could be explained
further
SEQUENCES
of functional
on the
study.
OF PMMA
groups
responsible
for
a~re~ation Concerning their
mutual
the
question
interaction
a s to w h i c h f u n c t i o n a l
f o r PMMA s t e r e o c o m p l e x
can be found
in the literature.
stereocomplex
is formed
groups
o f i-PMMA a n d
stereocomplex also formed
Liquori etal.
in consequence s-PMMA, thus
in polar solvents. in nonpolar
the basic role of ester self-aggregation Conclusive
results
( r e f . 104,106}.
groups,
it w a s f o u n d resolution bands pulse
and
of another
one of about
have
measured
of the polymer
and
in
o f i-PMMA a n d is essential;
From conventional
have
and
increases,
spinning spinning
whereas
protons shown
speeds speed,
the intensity
speed
(3"2:3).
that
of about
yield a high
{Fig. 17).
~-CH 3
The results
the spectrum
of this
and system
F r o m F i g . 17, i t
the intensity
o f t h e CH 2
o f t h e OCH 3 b a n d
does
m : ICH2+~-CH3/IOCH 3
t o 2.8 a t ~r = 5 kHz, w h e r e a s
of
of the
300 Hz w i d t h
1H MAS NMR s p e c t r a
At t h e s a m e t i m e , t h e r a t i o o f t h e i n t e n s i t i e s spinning
see Part
1H NMR s p e c t r a
o f t h e OCH3, CH 2 a n d
of a band
15-20 kHz width.
at various
with increasing
is
indicating
b y NMR s p e c t r o s c o p y
with a mixture
of respective
consists
with increasing
increases
formation
presented
in which the intensities
can be seen that
not.
the of ~-CH 3
of the
accumulated
(lower stereoregularity
NMR m e a s u r e m e n t s
part
a-CH 3 bands
were
was performed
to t h e n u m b e r
broad=line
that
the stereocomplex
a t 2 5 " C p = 40% (i.e., 60% o f m o n o m e r u n i t s
associated
been
gradually
r a t i o r = ( Y s / X i ) = 2.
NMR s p e c t r u m
correspond
that
by
opinions
interactions
the formation
both in stereocomplex
in this respect
The analysis
that
responsible
various
s-PMMA.
s-PMMA of lower stereoregularity VII-A) at the weight
explaining
evidence
are
( r e f . 33) a s s u m e d
of hydrophobie
After the finding
solvents,
of i- and
groups
formation,
the
131
-..--I C H 2 - - C - - L
(A)
...
(c)
Jn
(c)
(a)
/~
i
6
7
8
9
1'0
~in ppm
10
t i n ppm
(c)
(B) (a)
A 6
L 7
i 8
9
(c)
7
8
10
g
in ppm
Fig. 17. 1H MAS NMR s p e c t r a of t h e m i x t u r e i-PMMA (I : 97%; H : 3%) + s-PMNA (S = 65%; H = 31.5%) (1:2) in C6D 6 m e a s u r e d a t 60 MHz, 25"0, a n d d i f f e r e n t s p i n n i n g f r e q u e n c i e s Vr; (A): (u r ~ 1.5 kHz; (B): v r ~ 3.5 kHz; (C): v r ~ 5 kHz ( r e f . 104). value corresponding
to t h e n u m b e r of p r o t o n s i s 5 / 3 = 1.67.
As in t h e 1H
MAS NMR e x p e r i m e n t , we s e e o n l y t h e s p e c t r u m o f t h e u n a s s o c i a t e d p a r t of t h e p o l y m e r p l u s t h o s e l i n e s of t h e a s s o c i a t e d p a r t w h i c h h a v e b e e n n a r r o w e d b y t h e s p i n n i n g ; t h e a b o v e r e s u l t c a n be e x p l a i n e d s o t h a t o n l y t h e l i n e s of CH2 a n d ~-CH 3 g r o u p s of t h e a s s o c i a t e d p o l y m e r u n d e r g o
narrowing
by magic angle spinning.
By a s i m p l e c a l c u l a t i o n , it c a n b e s h o w n t h a t t h e
v a l u e m = 2.8 c o r r e s p o n d s
to t h e s i t u a t i o n w h e r e t h e 1H MAS NMR s p e c t r u m
r e v e a l s all t h e p r o t o n s o f t h e CH2 a n d =-CH 3 g r o u p s non-associated)
w h e r e a s t h e OCH 3 b a n d c o r r e s p o n d s
unassociated segments.
(both associated and o n l y to p r o t o n s of t h e
132 A s i m i l a r s i t u a t i o n w a s o b s e r v e d a l s o i n 13C NMR s p e c t r a m e a s u r e d w i t h t h e d e c o u p l i n g i n t e n s i t y ~H2/2~, ~ 5 kHz, w h e r e t h e i n t e g r a t e d t h e OCH 3 b a n d a m o u n t s to o n l y 79% of t h e q u a t e r n a r y a-CH 3 a n d CH2 c a r b o n s
i n t e n s i t y of
c a r b o n a n d of t h e
(a s a m p l e w i t h p -- 30% w a s s t u d i e d ) .
These results
i n d i c a t e t h a t t h e b a n d of 15-20 kHz w i d t h w h i c h c a n n o t b e n a r r o w e d b y m a g i c a n g l e r o t a t i o n a t v r ~ 5 kHz o r b y d i p o l a r d e c o u p l i n g a t 7H2/2~ = 5 kHz c o r r e s p o n d s corresponds
to OCH 3 g r o u p s , w h e r e a s t h e b a n d of 300 Hz w i d t h
to CH2 a n d ~-CH 3 p r o t o n s .
As t h e m o b i l i t y of t h e OCH 3 m e t h y l
g r o u p s i s r e l a t i v e l y h i g h e v e n in solid PMMA, it m u s t b e c o n c l u d e d t h a t in t h e s t e r e o c o m p l e x , t h e m o b i l i t y of t h e w h o l e e s t e r g r o u p i s g r e a t l y indicating that association takes place primarily through
reduced,
i n t e r a c t i o n of e s t e r
groups. C o n s i d e r a b l e h i n d r a n c e of e s t e r g r o u p m o t i o n i n t h e s t e r e o c o m p l e x is a l s o confirmed by the observed
n e g a t i v e v a l u e s of o p t i c a l a n i s o t r o p y
(ref. 42).
N e g a t i v e v a l u e s of o p t i c a l a n i s o t r o p y w e r e a l s o d e t e r m i n e d i n s e l f - a g g r e g a t e s of i-PMMA; a l s o , i n t h i s c a s e , t h e o b s e r v a t i o n w a s i n t e r p r e t e d ordering
of e s t e r g r o u p s a n d t h e i r c o o p e r a t i v e i n t e r a c t i o n s
by specific
( r e f . 42,46,62).
H i n d r a n c e of e s t e r g r o u p m o b i l i t y b y s t e r e o a s s o c i a t i o n i s a l s o i n d i c a t e d b y t h e r e s u l t s of d y n a m i c a l - m e c h a n i c a l m e a s u r e m e n t s , s h o w i n g t h a t i n s a m p l e s prepared
b y r a d i c a l p o l y m e r i z a t i o n of MMA p r o c e e d i n g in t h e PMMA
s t e r e o c o m p l e x g e l (or in i-PMMA " s o l u t i o n " ; in b o t h c a s e s , MMA s i m u l t a n e o u s l y s e r v e d a s " s o l v e n t " ) , t h e E - p r o c e s s i s d i s p l a c e d to h i g h e r t e m p e r a t u r e s 30-40"C) ( r e f . 85). the ordered
(by
T h e i m p o r t a n t r o l e of e s t e r g r o u p s i n t h e f o r m a t i o n of
stereocomplex structure
is also indicated by the viscometric
r e s u l t s of S h a c h o v s k a y a e t al. ( r e f . 72), i n d i c a t i n g t h a t in m i x t u r e s of i-PMMA w i t h MMA/MAA c o p o l y m e r s , t h e r e p l a c e m e n t of t h e e s t e r g r o u p s of t h e s-component by carboxyl groups
perturbs
t h e s t e r i c c o m p l e m e n t a r i t y of t h e
macromolecules. In the a bove cited p a p e r s ,
stereocomplex formation is supposed
to t a k e
p l a c e i n c o n s e q u e n c e of m u t u a l i n t e r a c t i o n s of t h e e s t e r g r o u p d i p o l e s of i a n d s-PMMA.
A somewhat d i f f e r e n t view c o n c e r n i n g the c h a r a c t e r
of
f u n c t i o n a l g r o u p i n t e r a c t i o n s l e a d i n g to s t e r e o c o m p l e x f o r m a t i o n w a s p u b l i s h e d b y C h a l l a e t al. ( r e f . 36,94,100).
Based on the finding that the
s t e r e o c o m p l e x i s f o r m e d b e t w e e n t h e i - c o m p o n e n t of PMMA a n d t h e s - c o m p o n e n t of e i t h e r PMMA, PiBMA o r PMAA a n d t h a t all t h e s e stereocomplexes exhibit the same X-ray pattern,
these authors
assume that
s t e r e o a s s o c i a t i o n t a k e s p l a c e i n c o n s e q u e n c e of i n t e r a c t i o n s of i-PMMA e s t e r g r o u p s w i t h t h e =-CH 3 g r o u p s of t h e s y n d i o t a c t i c c o m p o n e n t . T h e i m p o r t a n c e of e s t e r g r o u p d i p o l e i n t e r a c t i o n s i n s-PMMA self-aggregation
i s i n d i c a t e d b y t h e s p l i t t i n g of t h e C=0 s t r e t c h i n g
into three components with wavenumbers
vibration
e q u a l i n t h e solid s t a t e a n d i n
133 solutions
and
F i g . 18 a r e {a) a n d
of different
shown
120 rain (b) a f t e r
w h i c h all a g g r e g a t e s spectrum fraction
higher
self-aggregation
wavenumber
22,102,111,115).
indicating
( r e f . 111).
The absolute
determined
after
units
conclusion
that
(about
-
I
s-PMMA
in aggregated
of ordered
vibration
s-PMMA
s-PMMA in solution
i n IR s p e c t r a
are
of associated
monomer
( s e e T a b l e 3); t h i s l e a d s
one half) of the ester
I
at a
a t 1727 c m - 1 ( r e f .
in ordered
groups
It can
by a new band
bands
monomer units
I
(b) a f t e r
of the fraction
f r o m NMR s p e c t r a
I
groups
of ester
of the carbonyl
only a part
band
at as the
i n F i g . 18c.
o f t h e C--0 s t r e t c h i n g
of the fraction
the values
(immobilized)
c a .D
of ester
from spectrum
is shown
by a weak
In
of the aggregated
in this range
for the splitting
values
separation
p determined
aggregated
is exhibited
close contact
lower than
111).
a t 2 5 " C , 2 rain
(a) m a y b e r e g a r d e d
obtained
component)
dipole coupling
sequences,
(ref.
measured
T h e IR s p e c t r u m
spectrum
(1742 c m - 1 ) a n d
The reason
is the transition
spectrum
s-PMMA.
of the non-aggregated
that
IR s p e c t r a
c o o l i n g f r o m 100"C {i.e., f r o m a t e m p e r a t u r e
of s-PMMA (difference
considerably
in Raman and
of s-PMMA in toluene
are decomposed);
of non-aggregated
subtraction be seen
activity
IR s p e c t r a
to t h e
groups
in
are in close contact.
I
J
I
I
i
b
tO
..Q <[
,.
I
1790
I
I
1750
l
I
1710
I
I
,
-I 1670
cm Fig. 18. R a n g e of C:0 stretching vibrations in IR spectra of s - P M M A (S : 89.5%; H : 8.6~) in toluene m e a s u r e d at 25°C a n d 2 rain (a) or 120 rain {b) after cooling from 100°C. S p e c t r u m (c) s h o w s the range of C:0 stretching vibrations in IR spectrum of the aggregated fraction of s - P M M A (ref. 111).
134 Negative
values
mobility of ester The finding ordered ester
of optical anisotropy
groups that
interactions
structures
( r e f . 128).
the frequency
differences
coupling molecular
order
ester
Av b e t w e e n
and
of methyl
acetate
of the aggregates
structure
of i- and
diffraction
Liquori
and
of stereoregular
to these
structure
does
situated
above
mentioned,
and
diffractogram,
From energy
Boscher
assumes
form a double
is surrounded i/s
results
s-PMMA. original
structure
with a change
indicates
conformation
differs
(ref. 10-12).
of a slightly
found
theoretically somewhat
that
distorted
that
from Based i-PMMA 8/I
the i- and
radius
of ref. i00)
assume
the
a 60/4 helix. yield
of s-PMMA in the
the formation
Analysis
conformational that
structure
in stereocomplex
by Grigoreva
from the conformation
of the
of the stereocomplex
of s-PMMA is changed
proposed
(they
the lowest conformation
for s-PMMA forming
structure
of the backbone
chain conformation
with a glide plane,
only slightly
in
o f i-PMMA i n t h e s t e r e o c o m p l e x ,
that
M i h a i l o v e t al. ( r e f . 113) a s s u m e extended
deviating
b y m e a n s o f IR s p e c t r o s c o p y .
860 c m - I
chains
approximation)
(especially
on the conformational
a t 843 a n d
is connected
have
diffraction
more direct
doublet
the
with both
e t al. ( r e f . 100) c o n c l u d e d
authors
on the conformational
were obtained
to t h e c h a i n a x i s , below this plane.
and with the assumption
information
stereocomplex
to c o r r e s p o n d
propose
helical structure,
a 30/4 helix and
of X-ray
the
much from the
h e l i x i n w h i c h a n i-PMMA c h a i n o f s m a l l e r
these
f o r i-PMMA f o r m i n g
While the results
groups
studies
by an s-PMMA chain of larger
= I/2),
that
not differ
all e s t e r
the conformation
calculations
by
s-PMMA in the stereocomplex
the more recent
c h a i n f o r m (in t h e s t a g g e r e d
PMMA
was studied
with the glide plane parallel
o f i-PMMA i n t h e d o u b l e
in the stereocomplex
energy
that
Based on a fiber
time was assumed
authors,
t h e f o r m o f a 1 0 / 1 h e l i x ; i.e., i n a c o n f o r m a t i o n
stoichiometry
shown
in the
o f IR s p e c t r o s c o p y .
i-PMMA w h i c h a t t h a t
w i t h all ~ - C H 3 g r o u p s As we have already
radius
of
short-range
e t al. ( r e f . 33) c a m e t o t h e c o n c l u s i o n
According
has a conformational
s-PMMA chains
have
generates
s-PMMA chains
of pure
to t h e 5 / 1 h e l i x .
helix.
of model
isotropic
in the self-aggregates
conformation
also on a fiber
and
of
dependences
in simple esters
o f i-PMMA i n t h e s t e r e o c o m p l e x
the extended
of Raman spectra
the anisotropic
conformation
crystallization
l e a d to t h e f o r m a t i o n
of the concentration
vibration
of s-PMMA chains
of X-ray
diffractogram,
groups
structure
The conformational
the methods
groups
hindered
a t - P M M A ( r e f . 63).
in the liquid state,
B. C o n f o r m a t i o n a l
stereocomplex
considerably
also by studies
Measurements
o f t h e C=0 s t r e t c h i n g
of methyl
indicate
of crosslinked
of ester
was verified
systems
components
in associates
of
formation,
the
to a c o n f o r m a t i o n
e t al. ( r e f . 15); t h i s
proposed
i n r e f . 33.
135 H o w e v e r , r e c e n t d e t a i l e d a n a l y s i s h a s s h o w n t h a t t h e b a n d a t 860 cm -1, t h e i n t e n s i t y of w h i c h s t r o n g l y i n c r e a s e s in s t e r e o c o m p l e x f o r m a t i o n ( b o t h in s o l u t i o n a n d in t h e solid s t a t e ) , c o r r e s p o n d s to l o n g s - s e q u e n c e s in t h e e x t e n d e d c h a i n c o n f o r m a t i o n of t h e b a c k b o n e (in t h e s t a g g e r e d a p p r o x i m a t i o n ) ( r e f . 21,22; s e e Fig. 19a).
S e l f - a g g r e g a t i o n of s-PMMA in s o l u t i o n also l e a d s
to a n i n c r e a s e in t h e f r a c t i o n of long s - s e q u e n c e s in t h e e x t e n d e d c h a i n c o n f o r m a t i o n a n d t h i s t r e n d is m a i n t a i n e d also in solid s-PMMA i s o l a t e d from t h e s e s o l u t i o n s u n d e r c o n d i t i o n s w h e r e d e c o m p o s i t i o n of t h e a g g r e g a t e s d o e s n o t t a k e p l a c e ( r e f . 22).
In comparison with n o n - a g g r e g a t e d amorphous
s-PMMA w h e r e t t c o n f o r m a t i o n a l f o r m s also d o m i n a t e ( a c c o r d i n g to t h e o r e t i c a l c a l c u l a t i o n s a n d X - r a y d i f f r a c t i o n ; r e f . 9,17,18) in t h e s t e r e o c o m p l e x a n d in s e l f - a g g r e g a t e s , t h e e x t e n d e d c h a i n c o n f o r m a t i o n of s-PMMA p e r s i t s o v e r much l o n g e r d i s t a n c e s .
CH
c
o CH3
(o}s-PMMA
lb) OMTMGA
Fig. 19. E x t e n d e d c h a i n c o n f o r m a t i o n a l s t r u c t u r e of s-PMMA (a) a n d t h e e n e r g e t i c a l l y m o s t f a v o r e d c o n f o r m e r of DMTMGA (b) ( r e f . 108). T h e results of X-ray diffraction indicate that the conformational structure of s - P M M A
prepared b y solvent-induced crystallization (in vapors of
aggregation-promoting of s - P M M A
solvents) does not differ m u c h from the conformation
in the stereocomplex; K u s u y a m a
74/4 helix of large diameter.
et al. (ref. 24) propose for it a
At the same time, however, the fiber period 73.6
/~ of the 60/4 helix of s - P M M A
in the stereocomplex is roughly twice as long
as the fiber period (35.4 ~) a s s u m e d for the 74/4 helix in the ordered s-PMMA PMMA
alone (ref. 24,100).
It is clear that the conformational structures of
segments in helices with a large n u m b e r
of m o n o m e r
units per turn
(e.g., 60/4 or 74/4) can be generated from forms not differing m u c h staggered tt form.
from the
It m a y therefore be stated that the results of
conformational analysis obtained from IR spectra are in agreement with such helical b a c k b o n e structure.
In this sense, it is then possible to describe the
136 IR b a n d band
of long s-sequences
corresponding
I n t h e IR s p e c t r a for studies
found.
This is evidently bands
chain conformation
a conformationally
of the conformational due
structure
that
deuterated
o f PMMA ( r e f . 129) w a s a c o n f o r m a t i o n a l l y
analogs
crystalline
stereocomplex
X-ray
and
i-PMMA a n d
which is not present
in solutions
analysis
in the spectra
stating
o f i-PMMA. that
similar conformational
structure
of long sequences
not detected
in solutions
In addition the ester
groups
that
that
the mutual
energetically
in interaction
s-sequences be assumed
of
t h e i-PMMA c h a i n s
have
i-PMMA.
to
Contrary
a
structure
structure,
was
the orientation
cis orientation
o f C--0 a n d
( r e f . 130; s e e F i g . 1 9 b ) .
VIII-A), cis orientation
o f s - P M M A ( s e e F i g . 19a). by the results
of
C-CH 3 b o n d s
Based on the
w i t h i - o r s - P M M A , DMTMGA b e h a v e s
( r e f . 108; s e e P a r t
is supported
solid
the results
I n DMTMGA ( t h e d i m e r m o d e l o f
to exist also in s-PMMA chains
self-aggregates
band
of
of amorphous
confirms
with tt conformational
conformational
h a s to b e c o n s i d e r e d .
PMMA), it w a s f o u n d
of
o f i-PMMA.
to t h e b a c k b o n e
is the most favored finding
as in crystalline
sensitive
i n IR s p e c t r a
i n IR s p e c t r a
s-PMMA, the presence
of s-PMMA.
of the corresponding
This finding
in the stereocomplex,
band was not
of the stereocomplex
o f 800 c m - I , w h i c h i s p r e s e n t
deuterated
i-PMMA a n d
o f t h e IR s p e c t r a
bands
completed
in the range
sensitive
the conformationally
by stronger
Only in a recently
detected
( r e f . 22).
o f i-PMMA c h a i n s
to t h e c i r c u m s t a n c e
o f i-PMMA a r e o v e r l a p p e d study
a t 860 c m - 1 a s a
of the s-PMMA backbone
of the stereocomplex,
suitable
sensitive
in extended
to a helical structure
of ester
groups
in the stereocomplex In the latter
of the studies
s i m i l a r l y to
case,
of deuterated
may
and in
this assumption
s-PMMA analogs
( r e f . 116). As mentioned self-aggregates, appearance interesting one band
in the previous
paragraph,
mutual ordering
of ester
of a new carbonyl that
t h e IR s p e c t r u m
in the range
of s-PMMA in solutions
22).
This indicates
that
VII.
AND MOBILITY
Measurements s-PMMA
wavenumber.
vibrations,
aggregation
the mutual arrangement
is different
of s-PMMA
is manifested
by the
However, it is
of s-PMMA in the stereocomplex
where
self-aggregates
A. Effect of aggregation
at higher
o f C=0 s t r e t c h i n g
band
ORDERING
band
i n IR s p e c t r a groups
from that
exhibits
corresponding
does not take o f C=0 b o n d s
only
to t h e
place
(ref.
in s-PMMA
in the stereocomplex.
OF CHAINS
IN A G G R E G A T E S
OF PMMA
on segmental mobility of the chains
of 1H N M R
relaxation times T 2 in gels of mixtures of i- a n d
in C 6 D 6 (conc. 10%) have s h o w n
that in these systems,
present with the relaxation times T 2 : 36 ms, 0.9 m s a n d T h e first of these corresponds
protons are
15 /Js (ref. 104).
to relaxation times of pure i - P M M A
or s - P M M A
137
in C6D 6 s o l u t i o n a n d a g r e e s w i t h t h e l i n e w i d t h s in h i g h r e s o l u t i o n NMR s p e c t r a ; it i s a s s i g n e d shorter
to p r o t o n s in n o n - a s s o c i a t e d
u n i t s of PMMA.
relaxation times {indicating severely hindered
T h e two
mobility} a r e a s s i g n e d
to p r o t o n s of a s s o c i a t e d s e g m e n t s a n d t h e y a g r e e w i t h t h e s h a p e of t h e b r o a d - l i n e NhIR s p e c t r u m w h i c h c o n s i s t s of b a n d s of 300-400 Hz a n d of 15-20 kHz w i d t h .
As a l r e a d y m e n t i o n e d in P a r t VI-A, t h e b a n d of 15-20 kHz w i d t h
is a s s i g n e d
to e s t e r m e t h y l g r o u p s ~ w h e r e a s t h e b a n d of 300-400 Hz w i d t h is
assigned
to CH2 a n d ~-CH 3 p r o t o n s .
Also, w i t h t h e s e l f - a g g r e g a t e s
of
s-PMMA in t o l u e n e - d 8, s i m i l a r l i n e - w i d t h v a l u e s (A~ = 500 Hz} w e r e f o u n d f o r the backbone proton groups
( r e f . 110).
M e a s u r e m e n t s of 1H MAS N/*IR s p e c t r a a t v a r i a b l e t e m p e r a t u r e s NMR s p e c t r a
with strong
a n d of 13C
p r o t o n d e c o u p l i n g h a v e s h o w n t h a t with r e s p e c t
to
t h e b r o a d e n i n g o f t h e b a n d s of CH2 a n d ~-CH 3 p r o t o n s ~ t h e s y s t e m s s t u d i e d c a n be d i v i d e d i n t o two g r o u p s .
T h e f i r s t g r o u p is f o r m e d b y t h e m i x t u r e s
o f t h e s o l u t i o n s of i - a n d at-PMMA in C6D6~ w h e r e t h e v a l u e s of t h e a s s o c i a t e d f r a c t i o n a r e r e l a t i v e l y low (p = 30-40%} a n d w h e r e t h e m e n t i o n e d m e t h o d s l e a d to t h e n a r r o w i n g of b a n d s of 300-400 Hz w i d t h ( r e f . 104,106}. I n 1H MAS NMR s p e c t r a of t h e s e s y s t e m s , t h e b a n d s of p r o t o n s of a-CH 3 a n d CH2 g r o u p s
in a s s o c i a t e d s e g m e n t s h a v e the same width a s the c o n v e n t i o n a l l y
m e a s u r e d b a n d s of t h e p r o t o n s in n o n - a s s o c i a t e d
s e g m e n t s o r in s o l u t i o n s
w h e r e t h e a s s o c i a t i o n of PMMA d o e s n o t t a k e p l a c e . ~-CH 3 a n d frequency
CH2 g r o u p s
undergo
(in all t h e s e c a s e s } m o t i o n s a t a s i m i l a r
a n d t h a t t h e a s s o c i a t e d s e g m e n t s t h e r e f o r e c a n n o t be r e g a r d e d
static systems.
as
T h e w i d t h of 300-400 Hz e x h i b i t e d b y t h e b a n d s of a-CH 3 a n d
CH2 p r o t o n s i n c o n v e n t i o n a l l y m e a s u r e d s p e c t r a near-static
This indicates that the
is in t h i s c a s e limited b y
d i p o l a r i n t e r a c t i o n s w h i c h a r e a c o n s e q u e n c e o f t h e r e s t r i c t i o n of
t h e m o t i o n of t h e s e g r o u p s
in space~ i n c o n n e c t i o n w i t h t h e m u c h m o r e
s e v e r e r e s t r i c t i o n of t h e m o t i o n of t h e OCH3 g r o u p s .
All t h e s e d a t a f r o m t h e
m e a s u r e m e n t s o f l i t NMR s p e c t r a ~ t o g e t h e r w i t h t h e e v i d e n c e a b o u t t h e e x i s t e n c e of a s s o c i a t e d a n d n o n - a s s o c i a t e d
segments and the similarity with
t h e NMR b e h a v i o r of s w o l l e n g e l s of c h e m i c a l l y c r o s s l i n k e d p o l y m e r s , a r e c o m p a t i b l e w i t h t h e i d e a t h a t t h e s t e r e o c o m p l e x e s w i t h p = 30-40% h a v e t h e structure
of a n e t w o r k with the a s s o c i a t e d s e g m e n t s f o r m i n g the c r o s s l i n k
p o i n t s (Fig. 20a) {ref. 104,106,120}. The network structure
of t h e s t e r e o c o m p l e x o f PMMA w a s a l s o p r o p o s e d
by
R e h a g e e t al. ( r e f . 52,66p88~89~91) o n t h e b a s i s of v i s c o m e t r i c a n d dynamico-mechanical measurements.
It s h o u l d be mentioned t h a t also in t h e s e
s t u d i e s ~ g e l s of m i x t u r e s of i - a n d at-PMMA i n o - x y l e n e a n d i n t o l u e n e w e r e
investigated.
138
Fig. 20. S c h e m a t i c r e p r e s e n t a t i o n of t h e s t r u c t u r e s of PMMA s t e r e o c o m p l e x e s in s o l u t i o n s : (a) s t e r e o c o m p l e x w i t h p = 30-40% ( n e t w o r k model}; (b) s t e r e o c o m p l e x w i t h p ~ 95% ( d o u b l e h e l i c a l model} ( r e f . 106}. M i x t u r e s of s o l u t i o n s of i - a n d s-PMMA i n C6D 6 o r i n CD3CN w h e r e t h e v a l u e of t h e a s s o c i a t e d f r a c t i o n p is h i g h (more t h a n 80%) ( s i m i l a r l y a s t h e self-aggregates
o f s-PMMA i n t o l u e n e - d 8 ; p = 85%) e x h i b i t e d c o m p l e t e l y
d i f f e r e n t b e h a v i o r in NMR e x p e r i m e n t s ( r e f . 106,110).
C o n t r a r y to t h e
s t e r e o c o m p l e x w i t h p = 30-40%, s p i n n i n g a t t h e m a g i c a n g l e h e r e d o e s n o t a f f e c t t h e s h a p e of t h e IH NMR s p e c t r a ; a l s o , t h e p r o t o n d e c o u p l i n g w i t h 7H2/2w I 5 kHz d o e s n o t a f f e c t t h e s h a p e of t h e 13C NMR s p e c t r a of t h e s e systems.
T h i s i n d i c a t e s t h a t f o r t h e c o m p l e x e s w i t h p a b o v e 80% a n d a s well
as for the self-aggregates
of s-PMMA, t h e l i n e w i d t h ~ 400 Hz in 1H NMR
s p e c t r a is not limited by r e s i d u a l n e a r - s t a t i c s h a p e of t h i s b a n d s h o u l d r a t h e r
be d e s c r i b e d
with an effective correlation frequency a b o u t two o r d e r s
dipolar interactions but that the by motion isotropic in sp a c e
of 106-107 Hz; t h i s v a l u e is l o w e r b y
of m a g n i t u d e t h a n t h e c o r r e l a t i o n f r e q u e n c y
s-PMMA ( r e f . 106,110).
The retardation
of u n a s s o c i a t e d
of t h e m a i n c h a i n s e g m e n t a l m o t i o n is
e v i d e n t l y c a u s e d b y t h e h i g h d e n s i t y of c o n t a c t s (Fig. 20b). Also, t h e r e s u l t s o b t a i n e d b y t h e m e t h o d of p o l a r i z e d l u m i n e s c e n c e characterizing
the c h a i n mobility in s t e r e o c o m p l e x a g g r e g a t e s
DMF s o l u t i o n s ( r e f . 58) a r e i n v e r y
in v e r y d i l u t e
g o o d a g r e e m e n t w i t h t h e NMR r e s u l t s .
By
t h i s m e t h o d , it w a s f o u n d t h a t t h e m o b i l i t y of PMMA c h a i n s in t h e s t e r e o c o m p l e x is l o w e r b y a b o u t two o r d e r s n o n - a s s o c i a t e d PMMA.
of m a g n i t u d e t h a n f o r
E v e n t h e a b s o l u t e v a l u e s of t h e r e l a x a t i o n time Vw
d e t e r m i n e d f o r t h e s t e r e o c o m p l e x b y t h e m e t h o d of p o l a r i z e d l u m i n e s c e n c e a r e e q u a l to t h e v a l u e s of t h e c o r r e l a t i o n time Tc d e t e r m i n e d f o r t h e a s s o c i a t e d s e g m e n t s f r o m NMR s p e c t r a retardation
(v w a n d Tc a r e a b o u t 100 n s ) .
The pronounced
of t h e s e g m e n t a l m o b i l i t y of c h a i n s i n t h e s t e r e o c o m p l e x of PMMA
a n d i n s-PMMA s e l f - a g g r e g a t e s
w i t h a h i g h d e n s i t y of i n t e r a c t i o n s
indicates a completely different structure
(p £ 80%)
of t h e s e s y s t e m s f r o m t h a t of t h e
s w o l l e n g e l s of c h e m i c a l l y c r o s s l i n k e d p o l y m e r s (c.f. P a r t IV-C).
B. Chain ordering Studies of the stereocomplex of P M M A
and of s - P M M A self-aggregates b y
means of X-ray diffraction and vibrational spectroscopy have indicated that the conformationai s t r u c t u r e and ordering of chains of aggregates in solution
139 is t h e s a m e a s in solid s a m p l e s i s o l a t e d f r o m t h e s e s o l u t i o n s u n d e r preventing
d e c o m p o s i t i o n of t h e a g g r e g a t e s .
X-ray pattern
was observed
conditions
An i d e n t i c a l t y p e of c r y s t a l l i n e
f o r t h e s t e r e o c o m p l e x g e l s in b e n z e n e a n d f o r
solid s t e r e o c o m p l e x s a m p l e s ( r e f . 69).
A l t h o u g h c r y s t a l l i n i t y c o u l d n o t be
d e t e c t e d b y X - r a y d i f f r a c t i o n in c o n c e n t r a t e d
suspensions
of s-PMMA in BAC
( r e f . 38), a c l e a r c o n n e c t i o n b e t w e e n a g g r e g a t i o n of s-PMMA in s o l u t i o n a n d d e v e l o p m e n t of c r y s t a l l i n e s t r u c t u r e ( r e f . 22,38,102).
in solid s-PMMA c o u l d be d e m o n s t r a t e d
S i m i l a r l y , t h e r e s u l t s of IR s p e c t r o s c o p y
(in s e l f - a g g r e g a t e s
of s-PMMA, e s p e c i a l l y t h e e q u a l s p l i t t i n g of t h e c a r b o n y l v i b r a t i o n ) h a v e s h o w n t h a t b o t h i n t h e s t e r e o c o m p l e x a n d in t h e s e l f - a g g r e g a t e s the conformational structure the corresponding proved
of s - P H H A ,
of t h e s - c h a i n s is t h e s a m e in s o l u t i o n s a n d in
solid s a m p l e s (ref. 21,22,102,111).
by electron microscopy, self-aggregation
a f f e c t s t h e m o r p h o l o g y of solid s-PMHA ( r e f . 22). f r o m a c e t o n i t r i l e s o l u t i o n is s t r u c t u r e l e s s
At t h e s a m e time, a s
of s-PMMA in s o l u t i o n a l s o While solid s-PMMA i s o l a t e d
{Fig. 21b), solid s-PMHA i s o l a t e d
from toluene solution exhibits clearly fibrillar character
~a}
{Fig. 21a).
(b)
Fig. 21. Electron micrographs of s - P M M A (S -- 89.5%; H -- 8.5%) films prepared by evaporation of so]vent at room temperature from to]uene (a) and acetonitrile (b) solution (ref. 22). I n o n e of t h e o l d e s t p a p e r s c o n c e r n i n g t h e s t e r e o c o m p l e x of P M M A , e t al. (ref. 33) h a v e p r o p o s e d f o r t h i s s y s t e m a s t r u c t u r a l
Liquori
model w h e r e t h e
s-PMMA c h a i n s in a c o n f o r m a t i o n w i t h a g l i d e p l a n e lie i n " g r o o v e s " f o r m e d b y t h e 5/1 h e l i c e s of i-PMMA c h a i n e s (Fig. 22a).
H o w e v e r , in t h e c o u r s e of
time, e v i d e n c e is a c c u m u l a t i n g w h i c h i n d i c a t e s t h a t t h e f o r m a t i o n o f t h e s t e r e o c o m p l e x i s c o n n e c t e d w i t h t h e i n t e r a c t i o n of i - a n d s - s e q u e n c e s
which
a r e p a r e l l e l o v e r l o n g d i s t a n c e s , w i t h a b a c k b o n e c o n f o r m a t i o n n e a r to "all trans"
( s e e P a r t s V-B, V-C, VI-B, VII-A a n d VIII-B).
observation
Based on the
t h a t i n t h e s t e r e o c o m p l e x w i t h h i g h v a l u e s of t h e a s s o c i a t e d
f r a c t i o n p t h e s e g m e n t a l m o t i o n of t h e c h a i n s i s i s o t r o p i c a n d r e t a r d e d P a r t VII-A), t h e s t r u c t u r e
w a s p r o p o s e d f o r t h e f i r s t time ( r e f . 106; cf. Fig. 20b). diffraction and energy
(cf.
of t h e d o u b l e h e l i x o f t h e s t e r e o c o m p l e x of PMMA Based on X - r a y
c a l c u l a t i o n s , B o s s c h e r e t al. ( r e f . 100) a r r i v e d
at the
140
:C~c~ic l-Helix)
~Isotqctic
IC
le} F i g . 22. S c h e m a t i c r e p r e s e n t a t i o n of the chain ordering in the crystalline s t e r e o c o m p l e x o f PMMA: (a} m o d e l p r o p o s e d b y L i q u o r i e t al. ( r e f . 33}; (b} d o u b l e h e l i c a l m o d e l p r o p o s e d b y B o s s c h e r e t al. ( r e f . 100). T h e f i g u r e i s t a k e n f r o m r e f . 63.
conclusion
that
the stereocomplex
which an i-chain
consists
s-chain
with a 60/4 helical conformation
parallel
straight
agreement
chains
of i- and
with the structure
The self-aggregates with the stereocomplex Also, here
near
assumed forming
that
I01), based
has been
obtained
(together pairs
studies
12}; 2) t h e d e c r e a s e
the reaction
aggregation
s-sequences
than
of double
occurs
Quite recently,
of the aggregated
some minimum length
by interaction
with near-to-extended
further
mutual (cf. P a r t
V-B and
and
is the presence
of Pig.
with
the order
( r e f . 129} f a v o r s
chain conformation
interaction
formation
giving
of two chains;
fraction
stereoregularity
of s-PMMA self-aggregate
of s-PMMA self-aggregates
are paired,
e t al. ( r e f .
helices in s-PMMA aggregates
for s-PMMA of various
formation
it m a y b e
by Kusuyama
s-PMMA.
with a
segmental
of s-PMMA the chains
is admitted
of s-PMMA in the solution
of s-PMMA aggregate
for the generation
a long distance,
p = 0 f o r at-PMMA} i n d i c a t e
in the rate
concentration
in the solid state.
Based on this analogy,
( r e f . 111): 1) t h e v a l u e s
longer
of similar features
and
are parallel over
of crystalline
b y NMR s p e c t r o s c o p y
of s-sequences
The model assuming
chain form and with a retarded
structures
the existence
with the fact that
decreasing
where
sequences
(ref. 22,54,110).
on X-ray
supporting
by an
helix.
in solution
helix; this possibility
evidence
determined
of the double
also in the ordered
a double
(Fig. 22b).
of s-PMMA exhibit a number
to the extended
mobility in solution
helix in
is surrounded
s - P M M A ( r e f . 21} i s l i k e w i s e i n p r i n c i p l e
o f PMMA, b o t h
the interacting
conformation
of a double-stranded
with a 30/4 helical conformation
n = 2 of
a double
helix
3) a p r e r e q u i s i t e of long
in solutions.
Such
141 sequences
already
indicate
that
solutions
represent
the content
opinions
on the existence
( r e f . 24,101) s u p p o s e the existence solvent
sequences
solvent
studies
have
shown
that
condition
According
to t h e l a t t e r
for the formation conformational interaction
of the crystalline
structure
presence
structure
of s-PMMA chains
of long s-sequences
and
practically
thus
for the
structure On the
no residual
of solvent
of the crystalline
the solvent
e t al.
that
complexes with s-PMMA.
the simultaneous
references,
assume
of the crystalline
thin films containing
for the existence
Kusuyama
molecules is essential
of s-PMMA; they
inclusion
the effect of
in s-PMMA.
in the stabilization
crystalline
in ( r e f . 22).
in acetonitrile.
concerning
of solvent
structure
different
o-dichlorobenzene
not formed
structure
of very
necessary
are
of crystalline
directly
isomorphous
hand,
and
published
the presence
h e l i x ; IR r e s u l t s
is not very
toluene
been
that
have
of the crystalline
participates
forming
(nuclei) of a single
s-PMMA self-aggregates
Quite different
other
of these
of s-PMMA in acetonitrile,
In spite of that,
solvent
sections
is not a
form (ref. 22,38,102).
is a necessary
condition
o f s - P M M A ; it a f f e c t s
and
promotes
the stable
makes
possible
subsequent
only
the mutual
crystallization. This analysis
indicates
that
while s-PMMA and
one hand
and
i-PMMA o n t h e o t h e r
behavior
( r e f . 95,97), t h e s t r u c t u r e
i-PMMA, s - P M M A a n d it i s p r o b a b l y units
per
hand
by double
the stereocomplex very
of the crystalline
stereocomplex
formed
exhibit
PMMA (cf. P a r t
different phase
PMMA
is very
similar in
I I I - B ) ; i n all t h r e e
helices with a large
number
cases,
of monomer
turn.
VIII. OTHER AGGREGATES OF PMMA A. I n t e r a c t i o n s
of stereoregular
PMMA w i t h MMA m o n o m e r o r w i t h d i m e r
m o d e l o f PMMA Interactions
in the ternary
systems
PMMA-d8)/solvent
( r e f . 105) a n d
PMMA-d8)/eolvent
(ref.
MMA/(i- or s- or stereocomplex
DMTMGA/(i- or s- or stereocomplex
108) w e r e
studied
b y 1H NMR s p e c t r o s c o p y .
M/~
DMTMGA
HA ~.
/ CH3 C
/ HB
=
C
~H 3 CH 3
\
-
C
i H3 -
i COOCH 3
COOCH 3
CH 2
-
on
crystallization
- CH 3
I COOCH 3
142 The temperature NMR s p e c t r a
dependence
of solutions
interaction
of t h e c h e m i c a l s h i f t o f HA p r o t o n s
o f MMA i n v a r i o u s
o f MMA m o l e c u l e s w i t h DMF.
PMMA a c t s a s a f u r t h e r
component
solvents
revealed
In the system
interacting
Studies
of integrated
cases
a part
P M M A - d 8.
band
intensities
containing
This interaction
{10-15%} o f t h e DMTMGA m o l e c u l e s
In this interaction,
DMTMGA b e h a v e s
s-PMMA in interactions stereocomplex
{ r e f . 108).
arrangement
DMTMGA a n d aggregates These
in s-sequences
results
even
very
s-configuration contact
chain about
o f PMMA s t e r e o c o m p l e x
are in direct
relation
in the presence
short
oligomers
may be capable
chain
stable
The fact
( d i m e r s , t r i m e r s ~ etc.} i n
{on t h e NMR t i m e s c a l e }
with a certain
{ r e f . 105) f a v o r s
arrangement
the growth
o f MMA
of the nascent
tendency
o f MMA o f i-PMMA a n d
is active
the basis
of the so called replica
o f MMA p e r f o r m e d
also in the course
effect
studied
and in anionic
is identical
in the stereocomplex helix model.
of papers,
of stereoregular the structure
of i- and
supports
the double
o f i-PMMA p r o c e e d s
obtained
with an s-PMMA matrix are less unequivocal.
o f MMA i n t o l u e n e
systems;
the
PMMA h a s a l s o b e e n by
of the stereocomplex
While polymerization
the s-PMMA matrix on the stereoregularity
of
o f PMMA f o r m e d
are parallel over
definitely
is
both in radical
s-PMMA proves
presence
polymerization
and
polymerization
b y O r l o v a e t al. { r e f . 64),
with the structure
by the mixing of solutions s-chains
study
(ref. 49,62,113,138-140)
The observation'that
polymerization
process
o f MMA, w h e r e
in a number
o f MMA i n s o l i d m a t r i c e s
{ r e f . 141).
to s t e r e o c o m p l e x
o f i-PMMA l e a d s t o t h e f o r m a t i o n
Since the original
has been
(ref. 34,35,64,67,131-137} polymerization
s-PMMA chains
of the polymerization
polymerization
in the presence
s-PMMA and vice versa. the replica
polymerication
t h e i-PMMA m a t r i x .
The strong
i- and
of
or s-PMMA self-
o f i-PMMA ( s e e n e x t s e c t i o n ) .
of close and
formation
prepared
conformer
to t h e s o c a l l e d r e p l i c a
of the growing
t h e PMMA c h a i n s
B. R e p l i c a p o l y m e r i z a t i o n
replica
by the similarity of the
in the most favored
w i t h i-PMMA ( r e f . 108}, t o g e t h e r
molecules about
studied
can also replace
a n a n a l o g o f t h e PMMA
is explained
groups
in some
with
( s e e F i g . 19).
o f MMA p e r f o r m e d that
The behavior of ester
that
interact
s i m i l a r to s - P M M A {i.e.,
of s-PMMA and
w i t h i-PMMA, f o r m i n g
1H NMR s p e c t r a
shown
strongly
is
o f PMMA.
resolution
i- or s-PMMA-d 8 have
DMTMGA c a n l i n k u p i n s e l f - a g g r e g a t e s
geometrical
in high
1H
MMA/PMMA-d8/DMF,
w i t h MMA.
the same with i-PMMA-d8, s-PMMA-d 8 or the stereocomplex
o f DMTMGA i n s o l u t i o n s
in t h e
specific
by the replica
that
the
and
o f MMA i n t h e mechanism,
data
The negative
of the polymer
( r e f . 34,35,49,113,140}
again
long distances
generated
was explained
effect of by by
143 s e l f - a g g r e g a t i o n of s-PMMA; p r o b a b l y t h e g r o w t h of t h e p o l y m e r c h a i n c a n n o t p r o c e e d via r e p l i c a p o l y m e r i z a t i o n if a l m o s t all t h e s-PMMA matrix is p r e s e n t in t h e a g g r e g a t e d form in t h e p o l y m e r i z a t i o n s y s t e m (ref. 109).
C o n t r a r y to
t h e s t u d i e s b y Challa e t al. ( r e f . 34,35,132,133), in a r e c e n t p a p e r M a t s u z a k i e t al. ( r e f . 142) did n o t d e t e c t a n y e f f e c t of t h e s-PMMA matrix on t h e s t e r e o r e g u l a r i t y of t h e f o r m e d p o l y m e r d u r i n g p o l y m e r i z a t i o n in DMF a n d a c e t o n i t r i l e (i.e., in media w h e r e p r o n o u n c e d s e l f - a g g r e g a t i o n of s-PMMA d o e s n o t t a k e place).
F u r t h e r i n f o r m a t i o n on t h e r e p l i c a p o l y m e r i z a t i o n of MMA
c a n be o b t a i n e d from two r e v i e w a r t i c l e s ( r e f . 143,144}.
C. O t h e r s y s t e m s In t h i s s e c t i o n , we s h o u l d like to b r i e f l y m e n t i o n p a p e r s d e s c r i b i n g s t e r e o s p e c i f i c i n t e r a c t i o n s o f similar t y p e a s t h o s e of s t e r e o r e g u l a r PMMA, o b s e r v e d with o t h e r p o l y m e r s .
Challa e t al. ( r e f . 36,94,100,145,146) h a v e
s t u d i e d in d e t a i l i n t e r a c t i o n s in m i x t u r e s of s t e r e o r e g u l a r PMMA with s t e r e o r e g u l a r f o r m s of PMAA, b o t h in s o l u t i o n a n d in t h e solid s t a t e .
Of t h e
f o u r p o s s i b l e c o m b i n a t i o n s of s t e r e o r e g u l a r PMMA a n d PMAA, s t a b l e s t e r e o a s s o c i a t i o n t a k e s p l a c e o n l y in o n e c a s e (i.e.., b e t w e e n i-PMMA a n d s-PMAA).
The complex i-PMMA/s-PMAA, a l t h o u g h it is w e a k e r , r e s e m b l e s t h e
s t e r e o c o m p l e x of PMMA a n d a c c o r d i n g to X - r a y d i f f r a c t i o n , it h a s a p r a c t i c a l l y identical structure
( r e f . 94,100).
A n o t h e r a n a l o g of t h e s t e r e o c o m p l e x of PMMA h a s b e e n o b s e r v e d in m i x t u r e s of o p t i c a l l y a c t i v e e n a n t i o m e r s ; namely, i s o t a c t i c p o l y ( m e t h y l b e n z y l m e t h a c r y l a t e ) ( r e f . 147) a n d i s o t a c t i c p l y ( ~ - m e t h y l - ~ - e t h y l - ~ - p r o p i o l a c t o n e ) (ref. 148}.
The m e l t i n g p o i n t s o f t h e s e s t e r e o c o m p l e x e s in t h e solid s t a t e a r e
230"C a n d 202"C, r e s p e c t i v e l y ; in t h e s e c o n d c a s e , t h e m e l t i n g p o i n t o f t h e complex is h i g h e r b y a b o u t 40"C t h a n t h e m e l t i n g p o i n t s of t h e c o m p o n e n t s . Some e v i d e n c e also e x i s t s f o r t h e p r e s e n c e of a s t e r e o c o m p l e x c o m p o s e d of a c o m b i n a t i o n of i s o t a c t i e a n d s y n d i o t a c t i c p o l y ( m e t h y l ~ - c h l o r o - a c r y l a t e ) (ref. 149).
V i s c o e l a s t i c b e h a v i o r i n d i c a t e s t h e p r e s e n c e of s t r o n g i n t e r m o l e c u l a r
i n t e r a c t i o n s in t h e i - p o l y ( e t h y l m e t h a c r y l a t e ) w h i c h may be d u e to i - s e q u e n c e s ( r e f . 150).
I n t e r a c t i o n s of t a c t i c s e q u e n c e s a r e a l s o s u p p o s e d to
e x p l a i n t h e a g g r e g a t i o n b e h a v i o r o b s e r v e d w i t h s o l u t i o n s of p o l y m e t h a c r y l a t e s with m e s o g e n i c s i d e g r o u p s of t h e b e n z o i c acid p h e n y l e s t e r t y p e (ref. 151,152,153). IX.
CONCLUSIONS Long stereoregular sequences of PMMA have a strong tendency to mutual
interactions. B o t h the sequences of equal stereoregularity (i-i or e-s) and
s e q u e n c e s of d i f f e r i n g s t e r e o r e g u l a r i t y interaction.
(i-s) are capable of mutual
C o n s e q u e n t l y , t h e a g g r e g a t e s of s t e r e o r e g u l a r PMMA c a n be
144 d i v i d e d i n t o t h r e e t y p e s : 1) s e l f - a g g r e g a t e s
of i-PMMA; 2) s e l f - a g g r e g a t e s
of
s-PMMA; a n d 3) t h e s o c a l l e d s t e r e o c o m p l e x of PMMA f o r m e d b y t h e m i x i n g of s o l u t i o n s of i - a n d s-PMMA.
T h e s e t h r e e t y p e s of a g g r e g a t e s
t h e r m a l s t a b i l i t y a n d b y t h e e x t e n t of a g g r e g a t i o n self-aggregates
The
of i-PMMA e x h i b i t t h e h i g h e s t t h e r m a l s t a b i l i t y a n d t h e
self-aggregatres aggregates
differ by their
in t h e g i v e n s o l v e n t .
of s-PMMA e x h i b i t t h e l o w e s t t h e r m a l s t a b l i t y , w i t h t h e
of t h e s t e r e o c o m p l e x s o m e w h e r e i n b e t w e e n .
a t t e n t i o n h a s b e e n p a i d to t h e a g g r e g a t e s a l s o to t h e s e l f - a g g r e g a t e s
of s-PMMA.
The greatest
of t h e s t e r e o c o m p l e x a n d r e c e n t l y
Information about the self-aggregates
of i-PMMA i s s c a r c e d u e to t h e f a c t t h a t t h e c o n t e n t of t h e s e a g g r e g a t e s a l w a y s r e l a t i v e l y low, i r r e s p e c t i v e that the self-aggregates
close
of c r y s t a l l i n e i-PMMA m i g h t i n d i c a t e t h a t t h e
of i - P M M A i n s o l u t i o n a r e s m a l l c r y s t a l l i t e s .
The self-aggregates
of s-PMMA a n d t h e s t e r e o c o m p l e x of PMMA e x h i b i t a
n u m b e r of c o m m o n f e a t u r e s .
I n b o t h c a s e s , a g g r e g a t i o n is a v e r y c o m p l e x
p r o c e s s d e p e n d i n g on m a n y f a c t o r s . e f f e c t of time.
The observation
of i-PMMA a r e d e c o m p o s e d o n l y a t t e m p e r a t u r e s
to t h e m e l t i n g t e m p e r a t u r e self-aggregates
of t h e t y p e of s o l v e n t .
is
Of g r e a t i m p o r t a n c e i s , f o r e x a m p l e , t h e
T h e f o r m a t i o n of t h e " p r i m a r y " a g g r e g a t e s ,
r a p i d and which is p r o b a b l y p r e c e d e d conformational structure
w h i c h is r e l a t i v e l y
b y a n e v e n m o r e r a p i d c h a n g e of
of t h e s t e r e o r e g u l a r
s e q u e n c e s , i s followed b y t h e
v e r y slow p r o c e s s of t h e s o c a l l e d s e c o n d a r y a g g r e g a t i o n , w i t h s t e a d i l y i n c r e a s i n g particle size.
This p r o c e s s is d e t e c t e d with d i f f e r e n t s e n s i t i v i t y
by various physical methods. One of t h e d e c i s i v e f a c t o r s i n t h e s e l f - a g g r e g a t i o n s t e r e o c o m p l e x formation is the s t e r e o r e g u l a r i t y ordered
structure
interacting
of s-PMMA a n d i n
of p o l y m e r c h a i n s .
A stable
i s f o r m e d o n l y in t h o s e c a s e s w h e r e t h e l e n g t h of t h e
s e q u e n c e s is l o n g e r t h a n some minimum l e n g t h .
The actual values
o f t h i s m i n i m u m l e n g t h d e p e n d o n t h e s o l v e n t ; i n t h e c a s e of t h e s t e r e o c o m p l e x of PMMA, it w a s p o s s i b l e to c l a s s i f y t h e s o l v e n t s a s s t r o n g l y c o m p l e x i n g ( m i n i m u m l e n g t h of a s s o c i a t e d s - s e q u e n c e s a n d w e a k l y c o m p l e x i n g (q = 10 m o n o m e r u n i t s } . seif-aggregates
q : 3-4 m o n o m e r u n i t s }
I n t h e c a s e of
of s-PMMA, t h e e x p e r i m e n t a l l y f o u n d m i n i m u m l e n g t h q i s
e q u a l to 9 m o n o m e r u n i t s .
Also, t h e t h e r m a l s t a b i l i t y of t h e a g g r e g a t e s
determined by stereoregularity; formed by long stereoregular by short sequences.
the temperature
is
of " m e l t i n g " of a g g r e g a t e s
sequences is higher than for aggregates
The solvent has a less pronounced
formed
effect on the
t h e r m a l s t a b i l i t y of t h e a g g r e g a t e s . I n b o t h c a s e s ( s t e r e o c o m p l e x a n d s-PMMA s e l f - a g g r e g a t e s ) ,
t h e r a t e of
a g g r e g a t i o n i n c r e a s e s w i t h t h e i n c r e a s i n g c o n c e n t r a t i o n of t h e s o l u t i o n a n d it increases very rapidly with the decreasing temperature r o l e of s o l v e n t i n t h e a g g r e g a t i o n
of a g g r e g a t i o n .
p r o c e s s i s n o t q u i t e c l e a r so f a r .
The
145 Aggregation non-polar
of stereoregular solvents
the complexing such
PMMA t a k e s
even
which can strongly It is interesting
self-aggregation
For stereoregular
interact
basis
related
conformation
sequences turn. than
very
studies
near
sequences
of the i-chain,
stereocomplex
leading
i/s = I/1.5
to I / 2 .
The formation
by the much lower segmental in solution
the stereoregularity represent systems chains
of the components
where
the degree
participate
After removal of the solvent self-aggregates generated
aggregation
the morphological
turn;
crystalline
the chains
even
is very
the
in the solid state.
crystalline.
Thus,
Solid
the structure
of stereoregular
PMMA
As also for crystalline helix with a large
it may be stated
forms of stereoregular
In
o f PMMA e x i s t , t h e s t r u c t u r e
form a double
therefore,
helices can
formed.
or gels where
process.
that
the double
on
(p ~ 85%), a l m o s t a l l PMMA
properties
per
structure)
to
helices.
and
i-PMMA, it w a s f o u n d
Structures
is preserved
of the
helices is also
motion in the
network
by means of the aggregation
of monomer units
stereocomplex)
is large
from solutions
in this way is partially
can be affected
all three
on solvent,
of double
per
o f PMMA, i n d e p e n d e n c e
of s-PMMA or the stereocomplex
during
PMMA p r e p a r e d (including
and
of
helix is larger
stoichiometry
as compared
of the physical
of aggregation
in the formation
of the s-chain
2 orders
a
stereoregular
of the double
In the stereocomplex
points
The results
mobility; segmental
is slower by about
only the crosslink
o f PMMA a s s u m e
of monomer units
with the found
aggregates
segments.
structure.
o f PMMA, t h e r a d i u s
in agreement
The mobility
Both in the
the chains
number
of
role in the
to a g g r e g a t i o n .
the interacting
helix, with a large
manifested
non-associated
that
with some other
hindered.
chain
in both cases
In the stereocomplex
is so strong even
o f MMA.
with the stereocomplex
in the stereocomplex,
that
is not parallel.
the polymerization
play an important
is strongly
to the extended
indicate
form a double
that
groups
in the aggregates
of s-PMMA and
(e.g.,
on the
polymerization
to interaction
of s-PMMA and
the ester
of stereoregular
groups
aggregates
recent
that
formation
are formed
group
of solvent
in
polymers.
Both with the self-aggregates
interactions
the effect
of the so called replica
stereoregular
with
has not been observed
o f PMMA d u r i n g
PMMA, t h e t e n d e n c y
in
has no connection
with the carbonyl
to note that
s i m i l a r to t h e s t e r e o c o m p l e x
PMMA, it w a s f o u n d
of ester
Aggregation
of the stereocomplex
is the physical
chemically
parameter
of s-PMMA and on stereocomplex
The formation
aggregates
place both in polar and
the solubility
ability of the solvent.
solvents
chloroform).
process
and
that
number
the structure
of
PMMA (i-PMMA, s - P M M A ,
similar.
of the double
biological macromolecules.
helix type Stereoregular
so far
have
only been
PMMA's a r e t h e f i r s t
considered synthetic
with
146 polymers where double helices generated by physical interactions have been observed.
So f a r , t h i s s t r u c t u r a l a n a l o g y h a s n o t b e e n e x p l o i t e d in t h e
a p p l i c a t i o n s of s t e r e o r e g u l a r PMMA.
X.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
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149
114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150
P. S c h m i d t , B. S c h n e i d e r , S. Dirlikov a n d M. hlihailov, Eur. Polym. J., 11(1975}229. Z.A. K a r a p e t y a n , Ye.G. A t o v m y a n , V.P. R o s h c h u p k i n a n d B.R. S m i r n o v , Vysokomol. S o e d , A 25(1983)303. J. Dybal, B. S c h n e i d e r a n d FI. rdihailov, Coll. Czech. Chem. Commun., 49(1984)2259. J. S p ~ v a ~ e k a n d B. S c h n e i d e r , S c h u l t a g u n g " H F - S p e k t r o s k o p i e a n P o l y m e r e n " , R e i n h a r d s b r u n n , 1983, P r o c e e d i n g s , p. 78. J. S p ~ v ~ e k a n d B. S c h n e i d e r , Czech. J. P h y s . , B 24(1974)593. J. S p ~ v ~ e k , u n p u b l i s h e d . D. Dosko~ilov~ a n d B. S c h n e i d e r , P u r e Appl. Chem., 54(1982)575. U. J o h n s e n , Kolloid Z. P o l y m e r e , 178(1961)161. I. F e r n ~ d e z d e Pi~rota a n d A. Horta, Makromol. Chem., 182(1981)1705. J. S p ~ v ~ e k , I. F e r n a n d e z de Pi6rola a n d J. Dybal, u n p u b l i s h e d . Y. I n o u e a n d T. Konno, Makromol. Chem., 179(1978)1311. K.J. Liu, J. Polym. Sci., A-2,5(1967}1199. FI. Nagai a n d A. Nishioka, J. Polym. Sci., A-1,6(1968)1655. G.C. P i m e n t e l a n d A.L. McClellan, The H y d r o g e n Bond, F r e e m a n a n d Co., San F r a n c i s c o , 1960. J. Dybal, J. S t o k r a n d B. S c h n e i d e r , Coll. Czech. Chem. Commun., 47(1982) 2027. J. S p ~ v ~ e k , J. Dybal a n d B. S c h n e i d e r , E u r o p h y s . Conf. A b s t r . 9E(1985} P69. J. Dybal, J. S t o k r a n d B. S c h n e i d e r , Coll. Czech. Chem. Commun., 48(1983) 2072. R. B u t e r , Y.Y. Tan a n d G. Challa, J. Polym. Sci., P a r t A - l , 10(1972}1031. R. B u t e r , Y.Y. Tan a n d G. Challa, J. Polym. Sci., Polym. Chem. Ed., 11(1973)1003 R. B u r e t , Y.Y. Tan a n d G. Challa, J. Polym. Sci., Polym. Chem. Ed., 11{1973}1013. J. Cons, E.J. V o r e n k a m p a n d G. Challa, J. Polym. Sci., Polym. Chem. Ed., 13{1975}1699. J. Gons, W.O. S l a g t e r a n d G. Challa, J. Polym. Sci., Polym. Chem. Ed., 15{1977}771. J. Gons, E.J. V o r e n k a m p a n d G. Challa, J. Polym. Sci., Polym. Chem. Ed., 15(1977}3031. J. Cons, L.J.P S t r a a t m a n a n d G. Challa, J. Polym. Sci., Polym. Chem. Ed., 16(1978}427. L.K. Golova, Yu.B. Amerik a n d B.A. K r e n t z e l , Vysokomol. Soed, B 12(1970) 565. T. Fliyamoto, T. T o m o s h i g e a n d H. I n a g a k i , Plakromol. Chem., 176(1975)3035. M.H. Mihailov, S.K. Dirlikov, B. S c h n e i d e r , D. Dosko~ilov~, N. P e e v a a n d Z. G e o r g i e v a , Doklady Bolg. Akad. Nauk, 27(1974)1223. I-I. Yau a n d S.I. S t u p p , J. Polym. Sci., Polym. Chem. Ed., 23(1985)813. K. M a t s u z a k i , T. Kanai, C. I c h i j o a n d hi. Yuzawa, hiakromol. Chem., 185 (1984)2291. C.H. B a m f o r d , in " D e v e l o p m e n t s in P o l y m e r i z a t i o n - 2", Ed. R.N. Haward, A p p l i e d S c i e n c e P u b l i s h e r s , L t d . , L o n d o n , 1979, Chap. 5. G. Challa a n d Y.Y. Tan, P u r e Appl. Chem. 53(1981)627. J.H.G.M. L o h m e y e r , G. K r a n s e n , Y.Y. Tan a n d G. Challa, J. Polym. Sci., Polym. L e t t . Ed., 13(1975}725. J.H.G.hi. L o h m e y e r , Y.Y. Tan a n d G. Challa, J. hiacromol. Sci. - Chem. A, A14(1980)945. K. Hatada, S. Shimizu, Y. T e r a w a k i , K. Ohta a n d H. Yuki, Polym. J., 13 (1981)811. D. G r e n i e r a n d R.E. P r u d h o m m e , J. Polym. Sci., Polym. P h y s . Ed., 22(1984)577. G.R. D e v e r , F.E. K a r a s z , W.J. PlacKnight a n d R.W. L e n z , h i a c r o m o l e c u l e s , 8( 1975}439. J. t l r o u z , M. I l a v s k ~ , J. S p ~ v ~ e k a n d J. T r e k o v a l , Flakromol. Chem., 181(1980)277.
150 151 152 153 154. 155, 156' 157, 158,
J. S p r i n g e r a n d F.W. Weigelt, Makromol. Chem., 184(1983)1489. J. S p r i n g e r a n d F.W. Weigelt, Makromol. Chem., 184(1983}2635. H. Cackovie, J. S p r i n g e r a n d F.W. Weigelt, P r o g . Colloid Polym. Sei., 69(1984)134. P.E.M. Allen, D.M. Host, Van Tan T r u o n g a n d D.R.G. Williams, E u r . Polym. J., 21{1985)603. G. t e n B r i n k e , E. S c h o m a k e r a n d G. Challa, M a c r o m o l e c u l e s , 18(1985)1925. E. S c h o m a k e r , G. t e n B r i n k e a n d G. Challa, M a c r o m o l e c u l e s , 18(1985)1930. I. Katime, J.R. Q u i n t a n a a n d J. Veguillas, Eur. Polym. J, 21(1985)1075. E. S c h r 6 d e r , P l a s t e u n d K a u t s c h u k , 32{1985)321.
*References marked with an asterisk appeared very recently when the text was a l r e a d y c o m p l e t e ; t h e y a r e c i t e d in Table 1 only. ACKNOWLEDGEMENT The
authors
reproduce
acknowledge
the figures
the
p e r m i s s i o n of t h e
from t h e f o r m e r p a p e r s :
following p u b l i s h e r s
1) B u t t e r w o r t h
to
& Co., L t d . ,
G u i l d f o r d (Figs. 2,4); 2} Hitthig & Wepf V e r l a g , Basel (Figs. 6,7,10,11,13,14); 3} S p r i n g e r (Figs. 20,22).
V e r l a g , H e i d e l b e r g (Fig. 19); a n d 4} S t e i n k o p f f V e r l a g , D a r m s t a d t
81
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
AGGREGATION J. S P E V A C E K
OF S T E R E O R E G U L A R
POLY(METHYL
METHACRYLATES)
a n d B. S C H N E I D E R
Institute of M a c r o m o l e c u ~ r Chemistry, Czechos]ovak A c a d e m y 162 06 P r a g u e 6, C Z E C H O S L O V A K I A
of Sciences,
CONTENTS
I.
ABSTRACT
II.
INTNOIXJG~ION ................................ .......................
...........................................................
82
III.
C2-1ARAC'rI~IZATION OF S
83
~
~
A. Configurational structure
(stereoregularity)
B. Confornmtional structure of ~
IV.
V.
............................. of I ~
............
83
................................
85
C. Dynamic properties of stereoregular PMMA ........................
87
METHODS USED IN STUDIES OF RMMA AGGREGATION (A SHORT SURVEY OF THEIR POSSIBILITIES) ............................................
89
A. Methods for dilute solution studies
9]
...........................
B. Methods for studies of concentrated solutions, gels and of the solid state .....................................................
]00
C. Methods of molecular spectroscopy (NMR spectroscopy, vibrational spectroscopy) ...................................................
]04
FORMATION AND CHARACTER OF AGGREGATES OF PMMA ......................
]]0
A. Stoichiometry of ~
.............................
|] 0
B. Effect of degree of stereoregularity on the formation of aggregates (minimtRn length of aggregated sequences) ..................
stereocomplex
] ]3
C. Thermal stability and decomposition of aggregates
]]9
...............
D. Kinetics of aggregation and effects of thermal history E. Effect of solvent on the formation of aggregates VI.
LOCAL S
~
OF A C ~ T E D
.......... ]23
................
]26
SEQUENCES OF PMMA ....................
T30
A. C h a r a c t e r of the interactions of functional groups responsible for aggregation ................................................
VII.
!30
B. Conformmtional structure of the aggregates of stereoregular ...........................................................
]34
ORDERING AND MOBILITY OF CHAINS IN AGf~EGATES OF PMMA .............
]36
A. Effect of aggregation on segmental mobility of the chains
]36
B. Chain ordering VIII.
82
......
.................................................
]38
OF PMMA ..........................................
]4 ]
A. Interactions o f stereoreEular PMMA with MMA monomer o r with dimer model of PMMA ............................................
]4!
OTHER A ~ T E S
B. Replica polymerization of MMA ..................................
T42
C. Other systems
143
0001-8686/87/$24.50
..................................................
© Elsevier Science PublishersB.V.
82
IX.
CONCLUS IONS
X.
REFERENCES
I.
ABSTRACT
.......................................................
]4 3
........................................................
]4 6
I n t h i s r e v i e w , e x p e r i m e n t a l r e s u l t s o b t a i n e d i n s t u d i e s of a g g r e g a t i o n stereoregular evaluated.
of
(PMMA) a r e r e v i e w e d a n d c r i t i c a l l y
B e s i d e s a g g r e g a t i o n in s o l u t i o n , a t t e n t i o n is a l s o p a i d to t h e
corresponding aggregates
poly(methyl methacrylates)
ordered
structures
of s t e r e o r e g u l a r
in t h e solid s t a t e .
PMMA a r e d i s c u s s e d
T h r e e t y p e s of
in p a r a l l e l : 1) t h e
s t e r e o c o m p l e x of PMMA f o r m e d b y t h e m i x i n g of s o l u t i o n s of i s o t a c t i c {i) a n d s y n d i o t a c t i c (s) PMMA; 2) t h e s e l f - a g g r e g a t e s self-aggregates
of s-PMMA; a n d 3) t h e
of i-PMMA.
In the introductory
sections, information on the conformational structure
a n d d y n a m i c b e h a v i o r of s t e r e o r e g u l a r s t a t e is s u m m a r i z e d .
PMMA i n s o l u t i o n s a n d in t h e solid
I n P a r t IV, t h e p o s s i b i l i t i e s of v a r i o u s p h y s i c a l m e t h o d s
in o b t a i n i n g v a r i o u s t y p e s of i n f o r m a t i o n o n PMMA a g g r e g a t e s demonstrated.
PMMA a g g r e g a t e s
are cited.
T h e p r o b l e m s of t h e s t r u c t u r e following three parts.
of PMMA a g g r e g a t e s
t h e r m a l s t a b i l i t y of s t e r e o c o m p l e x a g g r e g a t e s in P a r t V.
a r e t h e s u b j e c t of t h e
I n f o r m a t i o n c o n c e r n i n g t h e s t o i c h i o m e t r y of t h e PMMA
s t e r e o c o m p l e x a n d t h e e f f e c t s of s t e r e o r e g u l a r i t y
discussed
are
With e a c h m e t h o d , t h e m a i n r e s u l t s o b t a i n e d i n s t u d i e s of
on the formation a n d
a n d s-PMMA s e l f - a g g r e g a t e s
is
F o r t h e s e s y s t e m s in v a r i o u s s o l v e n t s , t h e v a l u e s of
t h e m i n i m u m l e n g t h of s - s e q u e n c e s
necessary
for aggregation are given.
A t t e n t i o n i s a l s o p a i d to t h e t i m e - c o u r s e of a g g r e g a t i o n a n d to i t s v a r i o u s stages.
I n P a r t VI, b a s e d o n t h e r e s u l t s of NMR a n d v i b r a t i o n a l
s p e c t r o s c o p y , it i s s h o w n t h a t a g g r e g a t i o n b y i n t e r a c t i o n s of e s t e r g r o u p s . PMMA a g g r e g a t e s stereoregular
of s t e r e o r e g u l a r
PMMA i s c a u s e d
The backbone conformational structure
sequences assume an approximately tt structure.
t h e e f f e c t s of a g g r e g a t i o n o n t h e m o b i l i t y a n d m u t u a l o r d e r i n g in a g g r e g a t e s
are described.
double-helical structures are discussed.
in
i s a l s o d i s c u s s e d i n t h i s c h a p t e r ; it i s s h o w n t h a t t h e I n P a r t VII, of t h e c h a i n s
Experimental results indicating that
are formed in a g g r e g a t i o n
of s t e r e o r e g u l a r
PMMA
I n f o r m a t i o n o n s o m e o t h e r s y s t e m s d i r e c t l y r e l a t e d to t h e
a g g r e g a t i o n of s t e r e o r e g u l a r
PMMA ( i n c l u d i n g t h e " r e p l i c a p o l y m e r i z a t i o n " of
m e t h y l m e t h a c r y l a t e ) is s u m m a r i z e d i n P a r t VIII.
II.
INTRODUCTION I n 1961, W a t a n a b e e t al. ( r e f . 1) r e p o r t e d
t h a t i n s o m e s o l v e n t s , m i x i n g of
t h e s o l u t i o n s of s y n d i o t a c t i c (s) PMMA a n d i s o t a c t i c (i) PMMA l e a d s to t h e f o r m a t i o n of a g g r e g a t e s ,
connected with pronounced
c h a n g e s of t h e
83 rheological properties
of t h e m i x t u r e .
c a l l e d " s t e r e o c o m p l e x PMMA". aggregation
solvent.
Further
and the properties
with the stereoregularity
The aggregates
thus formed were
r e s u l t s i n d i c a t e d t h a t t h e d e g r e e of
of t h e a g g r e g a t e s
of t h e i n t e r a c t i n g
are critically connected
p o l y m e r s a n d with the kind of
O p i n i o n s o n t h e n a t u r e of t h e i n t e r a c t i o n s l e a d i n g to s t e r e o c o m p l e x
formation have undergone
c o n s i d e r a b l e c h a n g e s in t h e c o u r s e of time.
N e v e r t h e l e s s , s i n c e t h e v e r y f i r s t p u b l i c a t i o n s , it h a s b e e n q u i t e c l e a r t h a t the aggregation
is c a u s e d b y w e a k i n t e r a c t i o n s , w i t h t h e i r r e s u l t s
by cooperative effects.
geometrical and dynamical structure of p a p e r s .
enhanced
T h e c o n d i t i o n s of s t e r e o c o m p l e x f o r m a t i o n a n d i t s h a v e b e e n t h e s u b j e c t of a g r e a t n u m b e r
I n t h e c o u r s e s of t h e s e s t u d i e s , it w a s a l s o f o u n d t h a t s-PMMA
a n d i-PMMA a l o n e c a n f o r m a g g r e g a t e s
i n s o m e s o l v e n t s ( r e f . 2,3).
it w a s r e c o g n i z e d t h a t i n t h e a g g r e g a t e s chains form helical structures helical structures
Gradually,
of s t e r e o r e g u l a r
PMMA, t h e PMMA
which are in some r e s p e c t s
a n a l o g o u s to t h e
of b i o l o g i c a l p o l y m e r s .
B e c a u s e of t h i s a n a l o g y a n d the
circumstance that stereocomplex formation strongly affects the properties PMMA m e m b r a n e s ( r e f . 4), s t u d i e s of t h e p r o p e r t i e s streoregular
PMMA a g g r e g a t e s
still a t t r a c t
In the s t u d i e s of s t e r e o r e g u l a r
and structure
considerable attention.
PMMA a g g r e g a t e s ,
various physical and physico-chemical methods.
u s e h a s b e e n m a d e of
I n t h i s r e v i e w , we h a v e
m a d e a n a t t e m p t to d i s c u s s all t h e m o r e i m p o r t a n t f i n d i n g s i r r e s p e c t i v e the method by which they were obtained.
of
of
of
Nevertheless, the conclusions are
certainly strongly affected by the circumstance that our own speciality is NMR a n d v i b r a t i o n a l s p e c t r o s c o p y .
III.
CHARACTERIZATION OF STEREOREGULAR
Of the structural parameters affecting P M M A
PMMA aggregation, the most
important factors are the configurational and conformational structure of PMMA
and the mobility of the various P M M A
functional groups; therefore, in
this part, the most important results of the studies of these parameters and the conventions used in their description will be summarized.
A. C o n f i ~ u r a t i o n a l s t r u c t u r e
(stereoregularity)
of PMMA
T h e d i f f e r e n c e s in t h e c o n f i g u r a t i o n a l s t r u c t u r e
o f PMMA a r e t h e r e s u l t o f
t h e c i r c u m s t a n c e t h a t C~ c a r b o n s o f t h e PMMA m o n o m e r u n i t s f o r m pseudoassymmetric centers.
A l t h o u g h t h e Ca c a r b o n i s n o t o p t i c a l l y a c t i v e ,
t h e d a n d 1 c o n f i g u r a t i o n of t h e Ca a t o m s c a n b e d i f f e r e n t i a t e d of the chain.
by inspection
A d i a d c o n t a i n i n g two C~ c a r b o n s of e q u a l c o n f i g u r a t i o n ( d d o r
U) i s d e s c r i b e d a s a n i s o t a c t i c d i a d ( s o m e t i m e s a l s o a m e s o [m] d i a d ) . d i a d f o r m e d b y two Ca c a r b o n s of u n e q u a l c o n f i g u r a t i o n (dl o r Id) is d e s c r i b e d a s a s y n d i o t a c t i c diad (sometimes also as a racemic [r] diad).
The
84 I 3 Ca
--
CH 2
I C
=
0
I
0
\ CH 3
B y configurational structure of P M M A , diads in the polymer. a linear b a c k b o n e chain.
T h e purely i - P M M A
we mean
the distribution of m a n d
consists of m diads only a n d with
structure, all ester g r o u p s are situated on one side of the
T h e purely s - P M M A
consists of r diads only; with a linear b a c k b o n e
structure, the ester g r o u p s alternate on both sides of the chain. configurational determination
r
structure of P M M A
can be most simply described
of the content of m a n d r diads.
The b y the
This result alone does not
yield a n y information on the distribution of m a n d r diads in longer sequences
which
determine
the content of i- a n d s-sequences
strongly affects the aggregation
information on the m e c h a n i s m
the sequence parameter
unit is independent
chain, then the g r o w t h is determined length distribution is determined
Pm(PrZl-Pm)
In order to
of the g r o w t h of the polymer chain is needed.
If the addition of a n y m o n o m e r the polymer
of P M M A .
of various length, some
of the configuration of b y Bernoulli statistics a n d
b y a single probability
which is defined b y the content of m a n d r diads
( r e f . 5). A l r e a d y in 1H NMR s p e c t r a m e a s u r e d a t 60 MHz, t h e c o n t e n t o f ram, m r a n d rr triads
( o f t e n d e s i g n a t e d a s I,H a n d S, r e s p e c t i v e l y , a n d g i v e n i n %) c a n
be d e t e r m i n e d f r o m t h e r e l a t i v e i n t e n s i t i e s of t h e =-CH 3 b a n d c o m p o n e n t s (ref. 5).
D e t e r m i n a t i o n s of t h e c o n t e n t of I,H,S t r i a d s h a v e s h o w n t h a t o n l y
PMMA s a m p l e s p r e p a r e d
by radical polymerization exhibit sequence
populations corresponding samples prepared
to B e r n o u l l i s t a t i s t i c s .
I n o t h e r c a s e s (PMMA
b y a n i o n i c p o l y m e r i z a t i o n ) , t h e c o n f i g u r a t i o n of t h e c h a i n
e n d h a s to b e c o n s i d e r e d i n t h e d e s c r i p t i o n of c h a i n g r o w t h . h a s to be d e s c r i b e d depends
by Markov statistics.
Such growth
In c a s e s w h e r e monomer a d d i t i o n
o n t h e c o n f i g u r a t i o n of o n l y t h e l a s t d i a d , f i r s t o r d e r M a r k o v
s t a t i s t i c s a r e s u f f i c i e n t f o r t h e d e s c r i p t i o n of c h a i n g r o w t h a n d t h e two necessary
probability parameters
I,H,S t r i a d s .
c a n b e d e t e r m i n e d f r o m t h e c o n t e n t of t h e
By m e a n s of 1H a n d 13C NMR s p e c t r a m e a s u r e d a t h i g h e r
magnetic fields, the content of e v e n longer sequences
can be determined
(e.g., tetrads a n d pentads from the analysis of the C H 2 a n d a - C H 3 b a n d s in IH N M R
spectra m e a s u r e d
of first order M a r k o v
higher order prepared
at 220 MHz) in order either to verify the validity
statistics or to determine the parameters
s t a t i s t i c s ( r e f . 5).
For most s t e r e o r e g u l a r
of s o m e
PMMA s a m p l e s
by conventional methods, first order Markov statistics are adequate
f o r t h e d e s c r i p t i o n of t h e c o n f i g u r a t i o n a l s t r u c t u r e
of PMMA.
85 T h e e q u a t i o n s r e l a t i n g t h e c o n t e n t s of I,H,S t r i a d s w i t h t h e two independent first order
probability parameters
d e t e r m i n i n g c h a i n g r o w t h a c c o r d i n g to
M a r k o v s t a t i s t i c s a n d p e r m i t t i n g t h e c a l c u l a t i o n of t h e c o n t e n t of
i- and s-sequences
of v a r i o u s l e n g t h a r e g i v e n in P a r t V-B.
B. C o n f o r m a t i o n a l s t r u c t u r e
of PMMA
I n PMMA, c o n f o r m a t i o n a l i s o m e r s c a n be g e n e r a t e d
by rotation about three
t y p e s of s i n g l e b o n d s : 1) t h e b o n d s b e t w e e n t h e m e t h y l e n e g r o u p a n d t h e quaternary
c a r b o n , CH2-C; 2) t h e b o n d s b e t w e e n t h e q u a t e r n a r y
and carbonyl
c a r b o n s , C-CO; a n d 31 t h e b o n d s b e t w e e n t h e c a r b o n y l c a r b o n a n d o x y g e n , CO-O.
R o t a t i o n a b o u t b o n d 1 (CH2-C) d e t e r m i n e s t h e c o n f o r m a t i o n a l s t r u c t u r e
of t h e c h a i n b a c k b o n e a n d r o t a t i o n a b o u t b o n d 2 (C-CO) d e t e r m i n e s t h e o r i e n t a t i o n of t h e e s t e r g r o u p s w i t h r e s p e c t
to t h e c h a i n .
Rotation about
b o n d 3 (CO-O) n e e d n o t b e c o n s i d e r e d i n s t u d i e s of t h e c o n f o r m a t i o n a l structure
of PMMA b e c a u s e in all s i m p l e m e t h y l e s t e r s a n a l y z e d so f a r , t h e
e s t e r g r o u p w a s f o u n d to h a v e a p l a n a r s t r u c t u r e g r o u p in cis o r i e n t a t i o n with r e s p e c t assumed that this structure
with the ester methyl
to t h e c a r b o n y l ; t h e r e f o r e , it m a y b e
of t h e e s t e r g r o u p i s p r e s e r v e d
CH
CH
131
- c
a l s o in PMMA.
1- i 3 cH
c
--
2
The structures described
generated
i n t e r m s of t r a n s
b y r o t a t i o n a b o u t CH2-C b o n d s a r e o f t e n (t) a n d g a u c h e (g) f o r m s e v e n if t h e y d e v i a t e
somewhat from the strictly staggered In this
chain with a planar arrangement a s tt, t h e s t r u c t u r e s by & 120"as tg.
of t h e b a c k b o n e c a r b o n a t o m s i s d e s i g n a t e d
w i t h o n e of t h e b o n d s 1 o r 2 t u r n e d
o u t of t h e p l a n e
By r o t a t i o n a b o u t b o n d 2 (C-CO), s i x d i f f e r e n t o r i e n t a t i o n s
of t h e e s t e r g r o u p w i t h r e s p e c t structure
structures.
"staggered a p p r o x i m a t i o n " , t h e c o n f o r m a t i o n a l f o r m of t h e PMMA
to t h e c h a i n c a n be g e n e r a t e d
(ref. 61.
The
w i t h t h e ~-CH 3 g r o u p c o p l a n a r w i t h t h e e s t e r g r o u p a n d o r i e n t e d
t o w a r d s t h e c a r b o n y l is d e s i g n a t e d a s " c i s (or s y n ) o r i e n t a t i o n of t h e e s t e r group with respect
to a-CII3"; t h e s t r u c t u r e
w i t h t h e a-CH 3 g r o u p c o p l a n a r
with t h e e s t e r g r o u p a n d o r i e n t e d a w a y from t h e c a r b o n y l is d e s i g n a t e d as "trans
(or a n t i ) o r i e n t a t i o n o f t h e e s t e r g r o u p w i t h r e s p e c t
Structures
to ~-CH3".
with -CH2-groups coplanar with the ester group can also appear
in PMMA, a s t h e s e c a n a g a i n b e e i t h e r of c i s ( s y n ) o r t r a n s
(anti) t y p e .
86
R
C
C C
0 syn R
0 anti
(cis R)
(trans
R R)
I. i-PMMA. T h e f i r s t c o n s i d e r a t i o n s a b o u t t h e c o n f o r m a t i o n a l s t r u c t u r e i-PMMA w e r e c o n n e c t e d w i t h t h e a n a l y s i s of X - r a y p a t t e r n s i-PMMA w h i c h w e r e o r i g i n a l l y i n t e r p r e t e d
of
of c r y s t a l l i n e
b a s e d o n t h e a s s u m p t i o n ( r e f . 7)
t h a t t h e c h a i n s of i-PMMA i n t h e c r y s t a l l i n e s t a t e f o r m a h e l i x w i t h f i v e m o n o m e r u n i t s p e r two t u r n s the conformational structure as tg.
([5/2] helix).
I n t e r m s of t h e s t a g g e r e d
forms,
of t h e c h a i n in s u c h a helix c a n be a p p r o x i m a t e d
A better agreement with the X-ray patterns
c o u l d be o b t a i n e d w i t h
t h e ( 5 / i ) h e l i x ( r e f . 8) b u t e v e n t h i s model d i d n o t a g r e e w i t h t h e t h e o r e t i c a l c a l c u l a t i o n s ( r e f . 9,10), a c c o r d i n g to w h i c h t h e e n e r g e t i c a l l y m o s t f a v o r e d f o r m of i-PMMA c h a i n s is e v e n m o r e e x t e n d e d t h a n t h e 5/1 helix. ordering 11).
of t h e 5 / 1 h e l i c e s i n t h e u n i t cell p r e s e n t e d
some difficulties (ref.
T h e r e f o r e , a t h i r d model w a s p r o p o s e d w h i c h d e s c r i b e d
patterns,
the X-ray
a s s u m i n g t h a t t h e u n i t cell of c r y s t a l l i n e i-PMMA i s f o r m e d b y two
double-stranded
helices d i s p l a c e d by c/2 along the c axis (fiber axis) with
r e s p e c t to o n e a n o t h e r
( r e f . 11,12).
Each double strand
helices with identical sense and direction. structure
Also, t h e
c o m p r i s e s two 10/1
I n t h e 10/1 helix, t h e c h a i n
c a n b e d e s i g n a t e d a s t t , w i t h t h e a n g l e s ~ a n d ~' d e v i a t i n g f r o m
the strictly staggered
t t f o r m b y 25" a n d I 0 " , r e s p e c t i v e l y .
This is in v e r y
g o o d a g r e e m e n t w i t h t h e t h e o r e t i c a l c a l c u l a t i o n s of V a c a t e l l o a n d F l o r y ( r e f . 13), a c c o r d i n g to w h i c h i n t h e e n e r g e t i c a l l y m o s t f a v o r e d f o r m of i-PMMA t h e a n g l e s ~ a n d ~' d e v i a t e f r o m t h e s t a g g e r e d
t t f o r m b y 23" a n d I I ' ,
g r o u p s a r e c o p l a n a r w i t h ~-CH 3 w i t h a l t e r n a t i n g
the ester
syn(cis) and anti(trane)
ester group orientation. M e a s u r e m e n t s of w i d e - a n g l e X - r a y s c a t t e r i n g of a m o r p h o u s solid i-PMMA s a m p l e s i n d i c a t e ( r e f . 14) t h a t a l s o h e r e t h e t t c o n f o r m a t i o n a l s t r u c t u r e most populated with alternating
syn- and anti-ester
groups.
is t h e
Besides the tt
form, a m o r p h o u s s a m p l e s also c o n t a i n tg a n d g t forms, in a g r e e m e n t with t h e o r e t i c a l p r e d i c t i o n s of S u n d a r a r a j a n al. ( r e f . 15).
a n d F l o r y ( r e f . 9) a n d o f G r i g o r e v a e t
M e a s u r e m e n t s of e n d - t o - e n d
indicate that tt chain structures s o l u t i o n (ref. 16).
d i s t a n c e s i n s o l u t i o n s of i-PMMA
are the most highly populated even in
87 2. s-PMMA. F o r a l o n g time, c r y s t a l l i n e s-PMMA c o u l d n o t be p r e p a r e d ; therefore,
the first information on the conformational structure
of s-PMMA
w a s o b t a i n e d f r o m t h e o r e t i c a l c a l c u l a t i o n s ( r e f . 9,10), f r o m small a n g l e n e u t r o n and X-ray scattering
( r e f . 17) a n d f r o m w i d e - a n g l e X - r a y s c a t t e r i n g
a m o r p h o u s solid s a m p l e s ( r e f . 18). energetically most favored structure
Theoretical calculations indicated that the of s-PMMA i s t h e s l i g h t l y d e f o r m e d t t
f o r m of t h e c h a i n , w i t h s y n o r i e n t a t i o n of e s t e r g r o u p s w i t h r e s p e c t ( r e f . 9,10,19).
of
Calculations have further
to =-CH 3
s h o w n t h a t in a m o r p h o u s s-PMMA
a n d in s-PMMA s o l u t i o n s , t h e p r e s e n c e of t g f o r m s of t h e c h a i n a n d s y n a n d a n t i o r i e n t a t i o n s of e s t e r g r o u p s w i t h r e s p e c t
to t h e c h a i n a r e a l s o to be
expected.
T h e r e s u l t s of w i d e - a n g l e s c a t t e r i n g
( r e f . 18), of n e u t r o n
scattering
( r e f . 17) a n d d i e l e c t r i c m e a s u r e m e n t s
(ref. 20) h a v e c o n f i r m e d t h e
r e s u l t s of t h e t h e o r e t i c a l c a l c u l a t i o n s .
A n a l y s i s of i n f r a r e d
(IR) s p e c t r a
has
s h o w n ( r e f . 21,22) t h a t s-PMMA i n s o l u t i o n c o n t a i n s a l a r g e p r o p o r t i o n of l o n g sequences
of t h e t t s t r u c t u r e .
T h e c o n t e n t of l o n g t t s e q u e n c e s
d i f f e r s in
v a r i o u s s o l v e n t s b u t it i s a l w a y s l a r g e r t h a n in solod a m o r p h o u s PMMA. f i n d i n g i s in a g r e e m e n t w i t h t h e r e s u l t s of i n t e r m e d i a t e - a n g l e scattering
This
X-ray
(ref. 23) w h i c h i n d i c a t e s a c o n s i d e r a b l e c o n t e n t of 9 - to
ll-membered
s e q u e n c e s of t t s t r u c t u r e s
of t h e c h a i n in s o l u t i o n s of s-PMMA.
P a r t l y c r y s t a l l i n e s-PMMA c o u l d be p r e p a r e d crystallization.
A n a l y s i s of X - r a y p a t t e r n s
by solvent-induced h a s i n d i c a t e d ( r e f . 24) t h a t i n
c r y s t a l l i n e s-PMMA t h e p o l y m e r c h a i n s f o r m h e l i c e s w i t h a l a r g e n u m b e r of monomer units per turn
( f o r m o r e d e t a i l , s e e P a r t VI-B).
From this s h o r t s u r v e y ,
it c a n be s e e n t h a t t h e c o n f o r m a t i o n a l s t r u c t u r e s
of t h e c h a i n i n t h e e n e r g e t i c a l l y m o s t f a v o r e d f o r m s of i - a n d s-PMMA d i f f e r v e r y little; in b o t h c a s e s i n t h e m o s t f a v o r e d f o r m , t h e c h a i n s t r u c t u r e be a p p r o x i m a t e d a s t t .
can
T h i s f i n d i n g is i n a g r e e m e n t w i t h t h e a n a l y s i s of t h e
conformational structures
of d i m e t h y l e s t e r s o f g l u t a r i c a c i d d e r i v a t i v e s , t h e
s i m p l e s t m o d e l s of PMMA d i a d s ( r e f . 25).
In these models, represented
by the
g e n e r a l f o r m u l a (RI,R2,R3)C1-CH2-C3(R4,R5,R6), t h e r e l a t i v e s t a b i l i t y of c o n f o r m e r s i s l a r g e l y d e t e r m i n e d b y t h e i n t e r a c t i o n s of s u b s t i t u e n t s p a r a l l e l C1-Ri a n d C3-Rj b o n d s ( p a r a l l e l 1-3 i n t e r a c t i o n s ) .
on
It was s h o w n t h a t
p a r a l l e l 1-3 i n t e r a c t i o n s of t w o e s t e r g r o u p s a r e a p p r o x i m a t e l y e q u a l to t h o s e of o n e m e t h y l a n d o n e e s t e r g r o u p . possible straight models. structures
with the longest
s e q u e n c e of s p 3 c a r b o n a t o m s a r e p r e f e r r e d
in t h e s e
B o t h t h e s e e f f e c t s l e a d to t h e s i m i l a r i t y of t h e c o n f o r m a t i o n a l of s - a n d i-PMMA c h a i n s .
C. D y n a m i c p r o p e r t i e s PMMA
Moreover, structures
of s t e r e o r e g u l a r
PMMA
contains several types of single bond rotations, which lead to
various internal motions of the polymer.
The barriers to rotation about the
88 v a r i o u s t y p e s of b o n d s a r e of c o n s i d e r a b l y d i f f e r i n g h e i g h t a n d t h e r e f o r e t h e m o l e c u l a r m o t i o n s of PMMA a r e c o m p l i c a t e d a n d e x h i b i t a s t r o n g dependence.
T h e d y n a m i c b e h a v i o r of PMMA c a n be d e s c r i b e d
f u n c t i o n s of t h e i n t e r n a l m o t i o n s G(T).
by correlation
U s u a l l y it is a s s u m e d t h a t t h e
c o r r e l a t i o n f u n c t i o n i s of e x p o n e n t i a l c h a r a c t e r
so t h a t the d y n a m i c b e h a v i o r
of t h e v a r i o u s f u n c t i o n a l g r o u p s of PMMA c a n be c h a r a c t e r i z e d c o r r e l a t i o n time Tc o r b y t h e c o r r e l a t i o n f r e q u e n c y The temperature
temperature
by the
vc, w h e r e 1 / r c = 2~v c.
d e p e n d e n c e o f t h e c o r r e l a t i o n f r e q u e n c i e s o f s o l i d PMMA
o b t a i n e d f r o m NMR r e l a x a t i o n p a r a m e t e r s , d i e l e c t r i c m e a s u r e m e n t s a n d m e c h a n i c a l m e a s u r e m e n t s i s s h o w n i n Fig. 1, w h i c h is b a s e d o n t h e d a t a o f McCall ( r e f . 26).
F r o m t h i s f i g u r e , it c a n b e s e e n t h a t t h e e s t e r m e t h y l
g r o u p i s t h e m o s t mobile, e x h i b i t i n g l a r g e c o r r e l a t i o n f r e q u e n c i e s
e v e n below
90"K; t h e a - m e t h y l g r o u p i s s o m e w h a t l e s s mobile, w i t h t h e r o t a t i o n a b o u t t h e C-CH 3 b o n d s t o p p i n g
(on t h e NMR time s c a l e , Vc<104-105Hz) a t t e m p e r a t u r e s
ca. 140"K; c h a i n b a c k b o n e m o t i o n s e x h i b i t t h e l o w e s t c o r r e l a t i o n f r e q u e n c i e s and thus the lowest mobility at a given temperature;
somewhat h i g h e r is the
m o b i l i t y of t h e e s t e r g r o u p a s a whole, w h i c h i s p r o b a b l y c o u p l e d w i t h t h e backbone motions.
T h e d y n a m i c b e h a v i o r of solid PMMA i s s t r o n g l y a f f e c t e d
by stereoregularity.
The glass transition
in) l i e s a t t h e t e m p e r a t u r e i-PMMA ( r s f . 27).
around
{where the b a c k b o n e motions set
115"C f o r s-PMMA a n d a r o u n d 45°C f o r
The data on the glass transition temperature
Tg d i f f e r
s o m e w h a t a c c o r d i n g to t h e m e t h o d b y w h i c h t h e y w e r e o b t a i n e d ; w i t h e a c h s i n g l e m e t h o d , h o w e v e r , T g of s-PMMA is a l w a y s h i g h e r b y a b o u t 70°C t h a n Tg of i-PMMA.
T h e m i n i m a i n NMR r e l a x a t i o n time m e a s u r e m e n t s , of l o s s
a n g l e s in mechanical m e a s u r e m e n t s a n d in dielectric m e a s u r e m e n t s corresponding temperatures 27).
to v a r i o u s f u n c t i o n a l g r o u p s f o r s-PMMA t h a n
of PMMA a l w a y s lie a t h i g h e r
the corresponding
m i n i m a f o r i-PMMA ( r e f .
This difference indicates that the resistance
to t h e r e o r i e n t a t i o n of all
g r o u p s i s h i g h e r i n s-PMMA t h a n i n i-PMMA. I n g e l s c o n t a i n i n g 60% w / w o r m o r e of t h e p o l y m e r , i n t e r n a l m o b i l i t y i s s i m i l a r to t h e m o b i l i t y in a solid p o l y m e r ( r e f . 28). backbone appears mobile.
At r o o m t e m p e r a t u r e ,
the
a s r i g i d o n t h e NMR s c a l e a n d o n l y t h e m e t h y l g r o u p s a r e
T h e m o t i o n s of t h e CH2 g r o u p s
representing
backbone motions only
s e t i n a t c o n c e n t r a t i o n s of 60-50% of t h e p o l y m e r a t room t e m p e r a t u r e . more dilute solutions where aggregation
In
d o e s n o t t a k e p l a c e , t h e m o t i o n of
t h e c h a i n is i s o t r o p i c (ref. 29), t h e m o t i o n of t h e =-CIt 3 g r o u p c a n b e described
b y t h e m o d e l of d o u b l e r e o r i e n t a t i o n w i t h two c o r r e l a t i o n t i m e s , Vg,
characterizing
r o t a t i o n a b o u t t h e b o n d C-CH 3 a n d To, c h a r a c t e r i z i n g
i s o t r o p i c m o t i o n of t h e r o t a t i o n a x i s ( r e f . 28,29). model i s n o t a d e q u a t e f o r c h a r a c t e r i z i n g
the
The double reorientation
t h e m o t i o n of t h e e s t e r CH3 g r o u p ;
in v e r y d i l u t e s o l u t i o n s , i t s m o t i o n c a n b e d e s c r i b e d
b y m e a n s of t h e log ×2
89
8
6 ~4 2 0
I.
-2 -4
'
I
I
I
1031T K q
F i g . 1. T e m p e r a t u r e dependence of the correlation frequency, ~c, f o r t h e m o t i o n s i n PMMA: m a i n c h a i n m o t i o n (o); m o t i o n o f t h e e s t e r g r o u p a s a w h o l e (e); r o t a t i o n o f t h e = - C H 3 g r o u p (z~); a n d r o t a t i o n o f t h e e s t e r CH 3 g r o u p (m). T h e d a t a b a s e d o n t h e r e s u l t s o f NMR s p e c t r o s c o p y , dielectric studies a n d d y n a m i c m e c h a n i c a l m e a s u r e m e n t s a r e t a k e n f r o m r e f . 26. distribution depends
of correlation
on the stereoregularity
temperatures, than
t i m e s ( r e f . 30).
the values
for s-PMMA.
correlation
frequencies
i-PMMA a n d
IV.
of the chains
of correlation
Therefore,
Even in solutions,
in chloroform,
of the a-CH 3 group
Vo=2.6xl08Hz , ~g=l.6xl08Hz
( r e f . 29,31).
frequencies
self-aggregates various
and
structure
f o r i-PMMA
are
uo=Sxl08Hz, vg:l.6xl09Hz
for
f o r s - P M M A ( r e f . 29).
AGGREGATION
of the stereocomplexes
(A S H O R T
o f PMMA a n d o f t h e
o f i-PMMA, s - P M M A o r a t - P M M A * a l o n e h a s b e e n f o l l o w e d b y
physical
methods.
references
of papers
included.
This section
basic principles monographs
At corresponding
higher
for example, at 27"C the
METHODS U S E D IN S T U D I E S O F P M M A S U R V E Y O F T H E I R POSSIBILITIES)
The formation
are
the mobility
They are exhaustively
in which the respective will n o t b e c o n c e r n e d
of the various
methods
( e . g . , i n r e f . 32) b u t
the aggregation
of stereoregular
methods.
In this
section,
in studies
of the aggregation
rather
summarized
in Table 1 and
method was applied with the explanation
which
can be found
with a review
of
of the information
on
some specific
o f PMMA w h i c h w e r e g a r d
of the
in a number
PMMA w h i c h c a n b e o b t a i n e d
we shall also include
are
by these results
as interesting
obtained and
* T h e t e r m a t - P M M A will b e u s e d t o d e s c r i b e PMMAs w i t h s u c h low stereoregularity that they cannot be designated as i- or s-PMMA. Besides samples with relatively high contents of both S- and I-triads, we use this designation also for conventional radical-polymerized PMMA, a l t h o u g h t h i s would also be described as s-PMMA of lower steroregularity, in view of the low c o n t e n t o f I - t r i a d s .
90 TABLE 1 S u r v e y of m e t h o d s u s e d in s t u d i e s of f o r m a t i o n a n d s t r u c t u r e
of PMMA
s t e r e o c o m p l e x a n d PMMA s e l f - a g g r e g a t i o n Method
PMMA s t e r e o c o m p l e x PMMA s e l f - a g g r e g a t i o n
(ref.)
(ref.)
turbidimetry
33-37
38b
light scattering
39-45,157,158
38b,42a,46a,47a,b158 b
sedimentation
40,48-51
osmometry
37,43
s p i n l a b e l m e t h o d s (EPR, fluorescence,luminescence)
56-58
52c,53c,54b,55 c
t h i n - l a y e r a n d GPC c h r o m a t o g r a p h y 4 3 , 4 9 , 5 9 flow b i r e f r i n g e n c e
42,60,61
42a,46a,62a,63 c
viscometry
34-37,39-44,51,52, 64-77
38b,42a,46a,47a, b, 52c,53c,54b,66c,70 a, 76b,78c,79c,80b,81b, c
m e a s u r e m e n t of gel m e l t i n g p o i n t and cloud point
1,67,82-85
53c
dielectric measurements and thermally stimulated depolarization c u r r e n t s
52,86,87
52 c
d y n a m i c o - m e c h a n i c a l m e a s u r e m e n t s 85,88-91,154 c a l o r i m e t r y a n d similar m e t h o d s
35-37,50,51,90-99, 154,156
x-ray diffraction
33,37,49,50,69,83, 90,94,95,97,100, 154
spectrroscopy
22b,23b,c,24b,38b, 95b$97b,100b,101b, 102 ° , 22 b
electron microscopy
NMR
91 c
29,65,69,103-108
2a,b 3a, b,c,3 b, 47a,~,c,54b,102 b, 1 0 9 a , b , l l 0 a , b , l l 1b
i n f r a r e d a n d Raman s p e c t r o s c o p y
21,22,29,41, 112-114,129
other
61,155
22b~lo1b~102b~111 b,
I15U,116o,129 o
ai-PMMA
bs-PMMA Cat-PMMA w h i c h , b y t h e i r c h a r a c t e r , do n o t f i t i n t o a n y of t h e p a r a g r a p h s following s e c t i o n s { P a r t s V - VII}.
of t h e
We did n o t r e f r a i n from d e m o n s t r a t i n g
e v e n some c o n t r a d i c t o r y r e s u l t s o b t a i n e d b y t h e same m e t h o d b y v a r i o u s authors.
The l a r g e n u m b e r of m e t h o d s a n d of p a p e r s d e v o t e d to s t u d i e s of
t h e s t e r e o c o m p l e x (73 r e f e r e n c e s ) a n d to s t u d i e s of t h e e i n g l e s t e r e o r e g u l a r
91 PMMA's, including the aggregation of at-PMMA
(34 references) prevent a more
detailed analysis of various papers. In this section, all methods summarized in Table i have been divided into three groups: 1) methods for dilute solution studies (turbidimetry, light scattering, osmometry, sedimentation, chromatography,
spin label methods, thin-layer and GPC
mixing calorimetry, flow birefringence, viscometry);
2)
methods for studies of concentrated solutions, gels and of the solid state (viscometry, measurements of the gel melting point, dielectric measurements and thermally stimulated depolarization currents, dynamic-mechanical measurements, D S C calorimetry, X-ray diffraction, electron microscopyl; 3) methods of molecular spectroscopy (NMR spectroscopy, IR and R a m a n spectroscopyl. In our classification, solutions with a concentration less than ~1% were considered as dilute; naturally, this limit should not be regarded dogmatically.
The methods of molecular spectroscopy have been separated
partly because of their specific character and partly because this is our o w n specialization.
A. Methods for dilute solution studies I. Turbidity. Liquori et al. (ref. 33) have already shown that the formation of the P M M A
stereocomplex in polar solvents (DMF, acetonitrile) is manifested
by enhanced turbidity.
In these media, the size of the stereocomplex
aggregate particles evidently reaches such values that the particles precipitate from solution (size ranges ~i00 n m to several micrometers).
The
dependences of the turbidity on the composition of the i/s-PMMA mixtures exhibit a maximum which is used to estimate the stoichiometry
of the
stereocomplex (ref. 33-35,37). Turbidity increases also with increasing concentration of the solution (ref. 33). During heating, an abrupt decrease of turbidity is observed in a certain temperature range (refs. 33,36), indicating deaggregation of stereocomplex particles. The turbidimetric methods have been applied in a more complex manner in studies of s - P M M A
seif-aggregation in butyl acetate (BAC) (ref. 38).
In this
case, the integral and differential turbidity ratio methods were applied for characterization
of the aggregating particles; the turbidities were measured
at three different wavelengths.
The solution of s - P M M A which was studied in
B A C was dissolved at high temperature where aggregates are not present in the system and aggregate formation was then followed by the measurement of the time dependence of turbidity at various temperatures for solutions of various concentration;
attention was also paid to the effect of the thermal
history of the solution. From the ratios of turbidities measured at various wavelengths, the size of the aggregating particles could be determined (i.e.,
92 t h e m e a n p a r t i c l e d i a m e t e r , t h e i r c o n c e n t r a t i o n c [g cm - 3 ] a n d / o r number N [cm-3])--all this for various aggregation
times.
2. C l a s s i c a l l i g h t s c a t t e r i n g . A n g u l a r l i g h t s c a t t e r i n g m e t h o d of d e t e c t i n g t h e p r e s e n c e of a g g r e g a t e s c a s e s w h e r e t h e f r a c t i o n of t h e a g g r e g a t e d
their
is a v e r y s e n s i t i v e
in t h e s y s t e m e v e n in t h o s e
m a c r o m o l e c u l e s is so s m a l l t h a t it
c a n n o t be d e t e c t e d b y o t h e r m e t h o d s like o s m o m e t r y , v i s c o m e t r y o r NMR spectroscopy
( r e f . 38).
of t h e a g g r e g a t i o n transparent.
T h e f o r m a t i o n of a g g r e g a t e s
the self-aggregates apparent
C o n t r a r y to t u r b i d i m e t r y ,
it p e r m i t s c h a r a c t e r i z a t i o n
p r o c e s s e v e n a t i t s b e g i n n i n g w h e n t h e s o l u t i o n is q u i t e of t h e PMMA s t e r e o c o m p l e x (or of
of i - o r s-PMMA) l e a d s to a m a r k e d i n c r e a s e in t h e
v a l u e s of molecular w e i g h t ( l ~ ) a p p .
t h e v a l u e s of ( l ~ ) a p p
which are dependent
F o r t h e PMMA s t e r e o c o m p l e x ,
on the composition (i/s) exhibit a
maximum; s i m i l a r l y , a s in t h e c a s e of t u r b i d i t y ,
t h i s i s u s e d f o r e s t i m a t e s of
t h e s t e r e o c o m p l e x s t o i c h i o m e t r y (ref. 39,42}.
D u r i n g h e a t i n g , a d e c r e a s e of
( l ~ } a p p is o b s e r v e d
w h i c h i s a c o n s e q u e n c e of t h e
at certain temperatures,
d e c o m p o s i t i o n of t h e s t e r e o c o m p l e x a g g r e g a t e s i n c r e a s e of ( ~ ) a p p
( r e f . 40,42}.
The absolute
a s c o m p a r e d to t h e a d d i t i v e v a l u e of t h e m i x t u r e d e p e n d s
a l s o o n t h e c o n c e n t r a t i o n o f t h e s o l u t i o n ( r e f . 43).
T h e r e s u l t s o f Katime e t
al. ( r e f . 45) i n d i c a t e t h a t e q u i l i b r i u m v a l u e s of ( H ~ ) a p p a n d of t h e r a d i u s of g y r a t i o n Rg f o r t h e s t e r e o c o m p l e x i n DMF a r e r e a c h e d o n l y a f t e r a b o u t 10 days. Increased
v a l u e s of ( l ~ } a p p w e r e a l s o o b s e r v e d
in DMF ( r e f . 42,46) a n d i n BAC ( r e f . 47). certain critical temperature,
w i t h s o l u t i o n s of i-PMMA
By h e a t i n g t h e s o l u t i o n a b o v e a
a p a r t of t h e i-PMMA a g g r e g a t e s
is i r r e v e r s i b l y
d e c o m p o s e d ( r e f . 46,47} a n d in t h e f o l l o w i n g t h e r m a l c y c l e s t h e s c a t t e r i n g d i a g r a m s do not differ.
A c c o r d i n g to K u s a k o v e t al. ( r e f . 46), t h e a g g r e g a t e s
of i-PMMA i n DMF d e c o m p o s e a t 50"C; h o w e v e r , in s t u d i e s of i-PMMA in BAC, it w a s f o u n d t h a t a m o l e c u l a r s o l u t i o n c a n be p r e p a r e d heating at temperatures
a b o v e 100-130"C ( r e f . 47).
By m e a n s of l i g h t s c a t t e r i n g , a g g r e g a t i o n methylethylketone
of s-PMMA w a s p r o v e d i n
(MEK}, 2 - e t h o x y e t h a n o l a n d BAC ( r e f . 38,47).
yields molecular solutions at temperatures temperature,
only by prolonged
aggregation
t a k e s place.
s-PMMA
a b o v e 60"C; b y c o o l i n g to a l o w e r
T h e time c o u r s e of a g g r e g a t i o n of
s-PMMA i n BAC a t 55"C f o l l o w e d b y m e a s u r e m e n t s of l i g h t s c a t t e r i n g i n Fig. 2, w h i c h c l e a r l y s h o w s t h e g r a d u a l g r o w t h of s c a t t e r e d w i t h time.
E v e n w i t h s-PMMA, a g g r e g a t i o n
characterized aggregation
turns
light intensity
c a n be a p p r o x i m a t e l y
b y t h e i n c r e a s e i n t h e v a l u e s o f (Nl~)app.
from solution.
is s h o w n
into macroscopic separation
A f t e r s o m e time,
( p r e c i p i t a t i o n } of t h e p o l y m e r
93
I
I
I
1:=10
×
40
1'0
0'5
1"5
2"0
2'5
S,n 2 (el2} * c-~
F i g . 2. D e p e n d e n c e o f t h e r a d i a t i o n e n v e l o p e s o f s e l f - a g g r e g a t i n g s - P M M A (S = 91.5%, H = 7.5%) i n BAC a t 55"C o n t i m e T {rain); c o n c . 5 x l 0 - 3 g c m - 3 ; C : 0.02 m i n - 1 ( r e f . 47).
3. Osmometry. From t h e concentration dependence of osmotic pressure, the n u m b e r average molecular weight, Mn, can be determined.
The intermolecular
interactions of macromolecules in stereocomplex formation are manifested by an increase of the Fin values, while the absolute effect depends on the ratio (i/s) in the mixture (ref. 37,43). Osmometry was also applied in a study of aggregation of s - P M M A in toluene (ref. 54). Also in this case, several-fold higher values of FIn were observed, indicating participation of intermolecular interactions in the aggregation process.
The decomposition of s - P M M A
aggregates with increasing temperature is manifested by a decrease of FIn values. Aggregation of a t - P M M A polymerization)
was studied
s-PMMA, also in this case exists
concerning
aaddition
to papers
This could probably
finding
the solvent
plays
claiming aggregation be explained
prepared by radical
(ref. 52-55). a major role.
measurements
no aggregation
i n r e f . 52, o r p o s s i b l y
4. Sedimentation.
PMMA
in a similar way
the osmometric
also exists one paper
defined
(conventional
Some discrepancy
of at-PMMA in toluene.
in this
system
stereoregularity
different
molecular
In
(ref. 53,54), there
at at-PMMA in toluene
by different
by very
Similarly as with
( r e f . 52).
which is not
weight.
Similarly as in the preceding methods, the increase of
the weight of the aggregated molecules in the stereocomplex of P M M A
makes
possible their detection by the method of sedimentation velocities (ref. 40,48,49). From the areas under the gradient curves, the weight fraction of
94 stereocomplex aggregates
can be e s t i m a t e d .
d i a g r a m s , Miyamoto a n d I n a g a k i d e m o n s t r a t e
On t h e b a s i s o f s e d i m e n t a t i o n ( r e f . 49} t h a t in a d d i t i o n to t h e
s t e r e o c o m p l e x , f r e e m o l e c u l e s of PMMA a r e p r e s e n t
i n m i x t u r e s of i / s - P M M A in
a c e t o n e w i t h t h e r a t i o i / s = 1/1 a n d 2 / 1 , t h e n u m b e r of f r e e m o l e c u l e s b e i n g c o n s i d e r a b l y h i g h e r in t h e l a t t e r c a s e .
Ultracentrifugation was also applied
f o r t h e p h a s e s e p a r a t i o n of t h e p r e c i p i t a t e d of t h e y i e l d i n d e p e n d e n c e
stereocomplex and determination
o n t h e r a t i o (i/s} {ref, 50} a n d o n t h e c o m p o s i t i o n
of t h e mixed s o l v e n t (ref. 51}.
5. S p i n l a b e l m e t h o d s (EPR, f l u o r e s c e n c e ~ l u m i n e s c e n c e } .
A common f e a t u r e
of t h e s e m e t h o d s i s t h e a t t a c h m e n t , b y c h e m i c a l r e a c t i o n , of a l a b e l d e t e c t a b l e by the respective
m e t h o d , to i - o r s-PMMA.
T h e a t t a c h m e n t of a n i t r o x i d e
r a d i c a l to i-PMMA h a s m a d e PMMA s t e r e o c o m p l e x f o r m a t i o n a m e n a b l e to EPR studies
( r e f . 56}.
F r o m t h e i n t e n s i t y of t h e b r o a d l i n e d u e to l i m i t e d m o b i l i t y
of t h e r a d i c a l in t h e s t e r e o c o m p l e x , s t u d i e d i n d e p e n d e n c e o n t h e r a t i o {i/s} and on temperature,
the authors
m a k e c o n c l u s i o n s a b o u t t h e s t o i c h i o m e t r y of
the steroecomplex and about its "melting". i - a n d s-PMMA m a c r o m o l e c u l e s c a r r y i n g
T h e i n t e r m o l e c u l a r i n t e r a c t i o n s of
l u m i n i s c e n c e l a b e l s in d i l u t e DMF
s o l u t i o n s a r e a l s o m a n i f e s t e d i n t h e m e t h o d of p o l a r i z e d l u m i n e s c e n c e d u e to reduced
m o b i l i t y {ref. 58).
The authors
of t h i s p a p e r c h a r a c t e r i z e
q u a n t i t a t i v e l y t h e i n t r a m o l e c u l a r m o b i l i t y of t h e s y n d i o t a c t i c c o m p o n e n t of t h e s t e r e o c o m p l e x in d e p e n d e n c e on the s t e r e o r e g u l a r i t y solvent.
By t h i s m e t h o d , t h e time d e p e n d e n c e
c o u l d a l s o b e followed.
of s-PMMA a n d o n t h e
of s t e r e o c o m p l e x f o r m a t i o n
Contact carbazole and anthracene
s - a n d i-PMMA f a v o r t h e e n e r g y
transfer
l a b e l s a t t a c h e d to
a n d m a k e p o s s i b l e s t u d i e s of
s t e r e o c o m p l e x formation in dioxane by the f l u o r e s c e n c e t e c h n i q u e
6. C h r o m a t r o g r a p h i c m e t h o d s . a n a l y s i s of t h e p r o d u c t s c o u l d be s e p a r a t e d
( r e f . 57}.
By m e a n s of t h i n l a y e r c h r o m a t o g r a p h y
i n t o two c o m p o n e n t s :
a n d i-PMMA, r e s p e c t i v e l y
{ref. 49,59).
a m i x t u r e w i t h i / s = 1/1 p l u s s -
From this finding, the authors
c o n c l u s i o n s a b o u t t h e c o m p o s i t i o n of t h e p r i m a r y s t e r e o c o m p l e x .
measured
some
c o n c e r n i n g t h e s t e r e o c h e m i c a l c o m p o s i t i o n of t h e p r o d u c t s .
r e s u l t s of GPC c h r o m a t o g r a p h y
make
H o w e v e r , it
s h o u l d b e s t a t e d t h a t t h e 60 MHz 1H NMR s p e c t r a of t h e p r o d u c t s a t 30"C w e r e n o t well r e s o l v e d ( s e e r e f . 59}, t h u s i n t r o d u c i n g uncertainty
and
b y NMR m e t h o d s , t h e m i x t u r e s w i t h i / s = 1/2 o r 2 / 1
The
h a v e s h o w n t h a t t h e p a r t i c l e s of t h e PMMA
s t e r e o c o m p l e x i n DMF a s a w h o l e a r e c o n s i d e r a b l y l a r g e r t h a n t h e coils of i o r s-PMMA a l o n e ( r e f . 43}.
7. Mixing c a l o r i m e t r y .
Mixing c a l o r i m e t r y w a s a p p l i e d to
s t e r e o c o m p l e x s t u d i e s i n two p a p e r s
( r e f . 93,99).
PMMA
F r o m m e a s u r e m e n t s of t h e
95 h e a t o f mixing of s o l u t i o n s of i - a n d s-PMMA, Biro~ e t al. ( r e f . 93) h a v e d e t e r m i n e d t h e h e a t of s t e r e o c o m p l e x f o r m a t i o n , aHf, a n d h a v e a l s o s t u d i e d i t s d e p e n d e n c e on t h e r a t i o i / s , o n t h e s o l v e n t a n d on t h e s t e r e o r e g u l a r i t y of the s-component.
The l a r g e s t v a l u e s (aHf} w e r e f o u n d in DMF (conc. 1%},
w h e r e f o r i / s = 1/1.5 to 1/2 a n d s-PMMA of h i g h s t e r e o r e g u l a r i t y (S = 94%; H = 6%), aHf = -15 J / g .
Similar v a l u e s of AHf w e r e a l s o f o u n d in CC14 (ref. 99}.
8. Flow b i r e f r i n g e n c e . M e a s u r e m e n t s of flow b i r e f r i n g e n c e h a v e s h o w n t h a t t h e v a l u e s of s e g m e n t a l a n i s o t r o p y of t h e PMMA s t e r e o a o m p l e x in t o l u e n e a r e n e g a t i v e a n d of h i g h a b s o l u t e v a l u e , i n d i c a t i n g a c o n s i d e r a b l e d e g r e e of o r d e r i n g of t h e s e s y s t e m s (similar to t h a t , f o r example, in m a c r o m o l e c u l e s of t h e biological origin} ( r e f . 42,60).
The d e p e n d e n c e of t h e s e g m e n t a l
a n i s o t r o p y o n t h e r a t i o i / s i n d i c a t e d t h a t maximum o r d e r of s t e r e o c o m p l e x a g g r e g a t e s is a t t a i n e d a t t h e r a t i o i / s = 1/1.
The h e a v i e s t s t e r e o c o m p l e x
p a r t i c l e s f o r m e d at i / s = 1/2 a r e t h u s n o t n e c e s s a r i l y t h e b e s t o r d e r e d o n e s ( r e f . 60).
The a u t h o r s f u r t h e r
d e m o n s t r a t e t h e e f f e c t of t h e r m a l h i s t o r y o f
t h e s a m p l e s w h i c h c a n lead to f u r t h e r i n c r e a s e o f t h e o r d e r i n g in t h i s s y s t e m . N e g a t i v e v a l u e s of a n i s o t r o p y of h i g h a b s o l u t e v a l u e i n d i c a t i n g t h e p r e s e n c e of o r g a n i z e d s t r u c t u r e s
w e r e o b s e r v e d a l s o with t o l u e n e s o l u t i o n s of
i-PMMA (ref. 42,46,62} a n d w i t h PMMA of " s t e r e o b l o c k " s t r u c t u r e
(I = 46%; H =
28%; S = 33%); in t h e l a t t e r c a s e , t h e y a r e a s c r i b e d to i n t e r a c t i o n s of i - a n d s - s e q u e n c e s of t h e same molecule ( r e f . 62).
Negative and t e m p e r a t u r e
d e p e n d e n t v a l u e s of o p t i c a l a n i s o t r o p y w e r e a l s o o b s e r v e d w i t h n e t w o r k s of at-PMMA s w o l l e n in CC14. ( r e f . 63). 9. V i s c o m e t r y . As s e e n f r o m Table 1, v i s c o m e t r y is t h e most f r e q u e n t l y 1 5 1 5 u s e d m e t h o d in s t u d i e s of t h e s t e r e o c o m p l e x of PMMA. This c i r c u m s t a n c e ,
t o g e t h e r w i t h t h e c o m p l i c a t e d n a t u r e a n d c o m p l e x i t y of s t e r e o c o m p l e x a g g r e g a t e f o r m a t i o n , h a s led to a n u m b e r of e v i d e n t l y o r a p p a r e n t l y controversial findings.
S t e r e o c o m p l e x f o r m a t i o n is u s u a l l y a s s u m e d to b e
i n d i c a t e d b y t h e n o n a d d i t i v e d e p e n d e n c e of t h e r e d u c e d s p e c i f i c v i s c o s i t y ~ s p / C o n t h e r a t i o i / s in t h e m i x t u r e .
I n DMF (in w h i c h s t e r e o c o m p l e x
f o r m a t i o n h a s b e e n most o f t e n s t u d i e d } , t h i s d e p e n d e n c e e x h i b i t s a minimum a n d t h e c o r r e s p o n d i n g r a t i o i / s is a s s u m e d to c o r r e s p o n d to t h e s t o i c h i o m e t r y o f t h e s t e r e o c o m p l e x (ref. 34-37,43,68,76} (Fig. 3).
The time
d e p e n d e n c e o f ~sp/C in DMF e x h i b i t s a n i n i t i a l d e c r e a s e ( r e f . 44), w h e r e a s i t s temperature d e p e n d e n c e (ref. 40,64).
exhibits an increase in a certain temperature range
Also, in the d e p e n d e n c e of intrinsic viscosity [7] (although the
determination of this quantity is s o m e w h a t problematic - see further text) on the ratio i/s in DMF, a m i n i m u m w a s observed
(ref. 39,44). These results
indicate that in this m e d i u m the h y d r o d y n a m i c
volume of the stereocomplex
96
o
2
0
~
\----22222
I
0
I
I
I
0.2 0.4 0.{5Ys __0.8 1.0
F i g . 3. D e p e n d e n c e o f t h e r e d u c e d v i s c o s i t y , l s p / C v s . s - P M M A c o n t e n t Y s f o r m i x t u r e s o f i-PMMA (I : 94%; H = 3%) a n d s - P M M A (S : 80%; H : 7%} i n c h l o r o f o r m (x), b e n z e n e (o) a n d DMF (o) ( r e f . 35).
aggregates is smaller than would correspond to a mixture on non-interacting i- and s-PMMA molecules; i.e., compact particles are observed. A minimum in the dependence of reduced specific viscosity on the ratio i/s, besides in DMF, was also observed in acetonitrile, acetone, dimethylsufoxide (DMSO), methyl isobutyrate, tetrahydrofurane (THF), MMA, BAC and ethyl acetate (EtAc) (ref. 35,71). However, it has to be remembered that ,}sp/C also depends on further factors, especially on the time from the mixing of the solutions of i- and s-PMMA and on their concentration.
With increasing time and especially at
higher concentration (above 0.5%), the values of Wsp/C increase even in DMF, reaching finally higher than additive values (i.e., exhibiting a maximum in the dependence on the ratio i/s) (ref. 35,43,76). T h i s behavior is explained by a gradual formation of a three-dimensional network, with small regions of associated and
segments
concentration
playing may then
( r e f . 65,71) f o r m i x t u r e s Greater studies
a role of crosslink
of i- and
discrepancies
of stereocomplex
formation
In a number
dependence
o f ,~sp/C o n i / s i s c i t e d
weaker
of papers
of a three-dimensional
"tendency
contradiction
towards
of the result
Differences
in time
o f m i n i m a ( r e f . 35) o r m a x i m a
s-PMMA in acetone.
are found
or toluene.
formation
points.
explain the findings
in the results in nonpolar
obtained
aromatic
by viscometric
solvents
like benzene
(ref. 35,52,65,66,69), a maximum in the ( F i g . 3) a n d
network
formed
complex formation" documenting
this is connected
with the
as a consequence
of a
of these
the existence
solvents
( r e f . 35).
In
o f a m a x i m u m Wsp/C i n
97 t o l u e n e , b o t h f r o m m e a s u r e m e n t s of e q u i l i b r i u m v a l u e s ( a b o u t 1 m o n t h a f t e r m i x i n g of i - a n d s-PMMA s o l u t i o n s } ( r e f . 65,69} o r f r o m m e a s u r e m e n t s p e r f o r m e d 10 rain. a f t e r m i x i n g ( r e f . 35}, o t h e r p a p e r s i n d i c a t e t h a t i n t h i s solvent at concentrations
below 1%, t h e v a l u e s of Wsp/C i n d e p e n d e n c e
on
time, a f t e r s o m e i n i t i a l d e c r e a s e , a t t a i n e q u i l i b r i u m v a l u e s ( r e f . 67,74), sJLmilarly a s in DMF ( r e f . 44).
A s t e e p i n c r e a s e of Wsp/C w i t h t i m e i s h e r e
c i t e d o n l y f o r c o n c e n t r a t i o n s a b o v e 1%. observed
R e h a g e a n d W a g n e r ( r e f . 76) h a v e
a m i n i m u m e v e n i n t o l u e n e , if t h e m e a s u r e m e n t s w e r e m a d e
immediately a f t e r mixing of the solutions; a f t e r s e v e r a l h o u r s , t h e minimum p a s s e s o v e r into a maximum. indicate that the aggregates
T h e r e s u l t s of t h e l a t t e r p a p e r s
t h u s s e e m to
of t h e PMMA s t e r e o c o m l e x in DMF a n d in t o l u e n e
a r e of t h e s a m e t y p e . T h e v i s c o s i t i e s of m i x t u r e s o f s o l u t i o n s of i - a n d s-PMMA d e p e n d a l s o o n t h e m o l e c u l a r w e i g h t of t h e s t e r e o r e g u l a r their stereoregularity. the additive character
c o m p o n e n t s {ref. 37,65,71} a n d o n
Low s t e r e o r e g u l a r i t y of r e d u c e d
was probably the reason why
specific viscosity was observed
for
m~ixtures of i - a n d at-PMMA i n b e n z e n e o r i n t o l u e n e ( r e f . 70,71}. behavior indicating that interaction between highly stereoregular PMMA d o e s n o t t a k e p l a c e c a n be r e g a r d e d 3) ( r e f . 35,65 69}.
Additive f o r m s of
a s p r o v e d o n l y in c h l o r o f o r m (Fig.
L o h m e y e r e t al. ( r e f . 36} h a v e followed v i s c o m e t r i c a l l y t h e
i n t e r a c t i o n b e t w e e n i-PMMA a n d p a r t l y h y d r o l y z e d c o s y n d i o t a c t i c c o p o l y m e r MMA/MAA.
s-PMMA, w h i c h i s r e a l l y a
E v e n f o r r e l a t i v e l y h i g h d e g r e e s of
h y d r o l y s i s , w h e r e t h e m e a n l e n g t h o f MMA s e q u e n c e s i s r e l a t i v e l y s h o r t , in DMF a d e c r e a s e of v i s c o s i t y below t h e a d d i t i v e v a l u e w a s o b s e r v e d , characteristic
f o r t h e f o r m a t i o n o f t h e PMMA s t e r e o c o m p l e x .
which is
M e k e n i t s k a y a et
al. ( r e f . 74} s t a t e t h a t t h e r e s u l t s of v i s c o m e t r i c s t u d i e s c a n b e a f f e c t e d b y t h e c i r c u m s t a n c e t h a t two p r o c e s s e s
p r o c e e d in parallel:
1) f o r m a t i o n of s t
e r e o c o m p l e x p a r t i c l e s ; a n d 2) a g g r e g a t i o n o f t h e s e p a r t i c l e s . have observed
The authors
t h e a g g r e g a t i o n o f s t e r e o c o m p l e x p a r t i c l e s i n DMF, b u t n o t i n
toluene. I n a n u m b e r o f p a p e r s , t h e v a l u e s of i n t r i n s i c v i s c o s i t y w e r e o b t a i n e d b y e x t r a p o l a t i o n o f t h e v a l u e s of ~ s p / C to z e r o c o n c e n t r a t i o n a n d t h e i r d e p e n d e n c e o n t h e r a t i o i / s ( r e f . 39,44,70,71} o r o n t e m p e r a t u r e w a s followed.
( r e f . 42,71,74}
H o w e v e r , B e l n i k e v i t c h e t al. ( r e f . 44) call a t t e n t i o n to t h e
c i r c u m s t a n c e t h a t i n t r i n s i c v i s c o s i t i e s d e t e r m i n e d in t h i s w a y a r e n o t s u i t a b l e fox" c h a r a c t e r i z i n g aggregates.
unambiguously the hydrodynamic
b e h a v i o r of s t e r e o c o m p l e x
T h i s is b e c a u s e t h e t i m e d e p e n d e n c i e s of ~ s p / C e x h i b i t a
d i f f e r e n t c o u r s e f o r v a r i o u s c o n c e n t r a t i o n s , w h i c h is, i n t e r alla, m a n i f e s t e d a l s o so t h a t t h e v a l u e s of [~] d e t e r m i n e d b y d i l u t i o n of t h e b a s i c s o l u t i o n , w h i c h h a s b e e n s t a b i l i z e d f o r a c e r t a i n time, d e p e n d o n t h e c o n c e n t r a t i o n o f t h i s s o l u t i o n ( r e f . 40,44).
As s e e n f r o m Fig. 4, t h e v a l u e s of [W] i n
98
I
I
i
a 6o-
3o
I
I
}
b60
C
130
__
-
IOO
I
J
j
2
4
6
Cm × [0 3 (g cm-3)
F i g . 4. D e p e n d e n c e o f t h e i n t r i n s i c v i s c o s i t y o f m i x t u r e s o f s o l u t i o n s o f i-PMMA (I : 72%; H : 17%1 a n d s - P M M A (S : 91.5%; H = 7.5%) o n t h e t o t a l initial concentration c m a t m i x i n g i n DMF (a), d i o x a n e ( b ) , a n d c h l o r o b e n z e n e (c); . . . . . , a d d i t i v e v a l u e ( r e f . 44). dependence and
on the total concentration
below the additive
not mean that
aggregation
Viscometric results (ref. 42,46,47,76) and intrinsic
value.
viscosity
with measurement
does not take
also indicate
with increasing
was described
observed
at temperatures
and its measurements observed,
indicating
sufficiently indicating reduced
long time (several a slow generation
does
( r e f . 461 o f
i n DMF i s c i t e d .
an irreversible their
In agreement
decomposition
of a part
heating
a certain
above
(ref. 46,47).
60"C.
( F i g . 5). hours)
of large
behavior
have
After cooling of the solution
at 25"0, an increase association
specific viscosity
decrease
no anomalies in viscometric above
thus
o f i-PMMA i n s o l u t i o n
( r e f . 42) a n d
i n DMF o r BAC a f t e r
With s-PMMA in toluene,
lie b o t h a b o v e
value
place.
temperature
of light scattering,
critical temperature
with the additive
self-aggregation
both an increase
o f t h e i-PMMA a g g r e g a t e s
a t m i x i n g (c m) c a n t h e n
Agreement
of the values The values
increase
of ~sp/C with time is
~sp/C measured
with decreasing
formations
with time was observed
( r e f . 54).
been
f r o m 60"C
after
concentration,
A growth
also with solutions
of of
a
99
I
r
f
10
~8
2
~00
200
300 time,rain
Fig. 5. D e p e n d e n c e o f ~splc - [7] v s . time ([7] : 0.52, d e t e r m i n e d a t 60"C) f o r s a m p l e s-PMMA (S = 89.5%; H = 8.5%) in t o l u e n e a t 25"C: c : 4.47 (o); 2.79 ( , ) ; 2.03 (/'); 1.4 (-); 0.86 ($) gL -1 ( r e f . 54). s-PMMA in BAC.
An a n o m a l o u s c o n c e n t r a t i o n d e p e n d e n c e of Wsp/C a n d g r o w t h
o f v i s c o s i t y w i t h time, i n d i c a t i n g t h e f o r m a t i o n of a n e t w o r k s t r u c t u r e , was o b s e r v e d a l s o w i t h s-PMMA in t o l u e n e a n d o - x y l e n e ( r e f . 76).
Katime e t al.
( r e f . 80,81) h a v e d e t e c t e d a n o m a l i e s in t h e t e m p e r a t u r e d e p e n d e n c e o f [7] w i t h s-PMlVlA in d i f f e r e n t s o l v e n t s , w h i c h t h e y i n t e r p r e t b y a c o n f o r m a t i o n a l t r a n s i t i o n b u t a c o n n e c t i o n w i t h a s s o c i a t i o n is a d m i t t e d .
However, similarly
a s w i t h t h e s t e r e o c o m p l e x , a l s o in t h e s e p a p e r s t h e d e t e r m i n a t i o n of i n t r i n s i c v i s c o s i t y r a i s e s some d o u b t s (see r e f . 54). Contradictory data have been published concerning the aggregation b e h a v i o r of at-PMMA.
B o r c h a r d e t al. ( r e f . 52,66) h a v e o b s e r v e d a maximum
in t h e t e m p e r a t u r e d e p e n d e n c e of ~/sp/C, a s well a s a n a n o m a l o u s c o n c e n t r a t i o n d e p e n d e n c e w i t h s o l u t i o n s of at-PMMA in t o l u e n e ; t h i s t h e y e x p l a i n b y i n t r a m o l e c u l a r a s s o c i a t i o n of s h o r t i - a n d s - s e q u e n c e s i n t e r a c t i o n s of stereocomplex type).
(i.e.~ b y
C o n t r a r y to t h i s , t h e f i n d i n g t h a t a l s o
w i t h at-PMMA in t o l u e n e t h e v a l u e s of ~sp/C a r e t i m e - i n d e p e n d e n t a n d e x h i b i t the conventional linear concentration dependence argues against the existence of a g g r e g a t e s in t h e s e s y s t e m s ( r e f . 54,76).
In t h e s e cases, an important
f a c t o r p r o b a b l y is t h e m o l e c u l a r w e i g h t o f at-PMMA.
The r e l a t i v e l y h i g h
v a l u e s of t h e H u g g i n s c o n s t a n t (k H ~ 1) i n d i c a t e t h e e x i s t e n c e of some i n t e r m o l e c u l a r i n t e r a c t i o n s in s o l u t i o n s o f at-PMMA in a c e t o n i t r i l e , c h l o r o b u t a n e a n d p - x y l e n e ( r e f . 53,54,78,79).
100 B. M e t h o d s for studies of concentrated solutions, gels a n d of the solid state. i. Rheology. It follows already from the p a r a g r a p h concerning the viscometric behavior of dilute solutions that with increasing concentration and time, the interactions between s- a n d i - P M M A in D M F
lead to the
formation of a gel. Mixing of concentrated solutions of i- and s - P M M A several per cent) leads to almost instantaneous gel formation.
(conc.
F r o m the
macroscopic point of view, these gels exhibit a sharp melting point considerably d e p e n d e n t on the stereoregularity of s - P M M A
(ref. I).
Similarly,
a d e p e n d e n c e on the stereoregularity of i - P M M A could be expected but this has not been studied.
It w a s found that gel formation does not take place if
the molecular weight of i- or s - P M M A
decreases below a certain limit (N~ <
i000) (ref. 82,83). The d e p e n d e n c e of the gel melting temperature on the total concentration (ref. 1,85) and on solvent (ref. 67) w a s studied.
Gel
formation w a s observed also for mixtures of solutions of i- a n d a t - P M M A acetone (ref. 84). Methodically similar to the above-mentioned also are the studies of aggregation of a t - P M M A
in
investigations
in CCI 4 or in p-xylene from
m e a s u r e m e n t s of cloud-point curves (ref. 52). Viscometry w a s applied to studies of mixtures of concentrated solutions (conc. 2 - 10%) of i- a n d a t - P M M A
in benzene, D M F
a n d toluene (ref. 70,75).
In d e p e n d e n c e on the ratio i/at-PMMA, the viscosity exhibits an e x t r e m u m a n d approaches additive behavior with increasing temperature, with the nature of the solvent playing some role. F r o m the temperature d e p e n d e n c e of viscosity, 7, using the relation w - A exp[(AH ;~ - TaS~)/RT], the activation enthalpy AH ;~ a n d activation entropy aS ;~ of the viscous flow has been determined.
T h e relatively high values of these quantities found in D M F
(AH ;~
= 31 kcal/mol; AS~ = 70 cal/mol) indicate that the flow is accompanied b y decomposition of strong intermolecular b o n d s a n d b y a considerable disordering of supermolecular structures (ref. 75). T h e presence of rigid organized structures is indicated b y viscometry also in 10% solutions of i - P M M A alone in benzene (ref. 70). T h e viscoelastic behavior of gels of the P M M A
stereocomplex in o-xylene
(conc. 5-12%) w a s studied b y dynamicomechanical techniques (i.e., b y the m e a s u r e m e n t of the time d e p e n d e n c e s of the real a n d imaginary c o m p o n e n t s of t h e s h e a r m o d u l u s ( s t o r a g e m o d u l i G' a n d l o s s m o d u l i G") ( r e f . 88,89,91). A g r a d u a l l o w e r i n g of t h e t e m p e r a t u r e
to a v a l u e w h e r e g e l f o r m a t i o n t a k e s
p l a c e is m a n i f e s t e d b y a s t e e p i n c r e a s e of G' a n d G" ( t h e c h a n g e of G' in a narrow temperature
r a n g e a m o u n t s to 8 o r d e r s )
(Fig. 6).
Viscoelastic
m e a s u r e m e n t s i n d i c a t e t h e f o r m a t i o n of a n e t w o r k v e r y s i m i l a r to t h e g e l s of c h e m i c a l l y c r o s s l i n k e d p o l y m e r s a n d it i s a s s u m e d t h a t t h e c r o s s l i n k p o i n t s are represented
by v e r y small c r y s t a l l i n e r e g i o n s .
101 The t e m p e r a t u r e d e p e n d e n c e s of t h e l o s s t a n g e n t (tg6 = G"/G') of b l e n d s of i - a n d s-PMMA a n n e a l e d f o r 120 h r s at 140"C a r e a s y m m e t r i c a l a n d e x h i b i t
togS' tog
if,
G"534
0log ~.
0 -1
30
I
I
50
I
I
I
J
90 temperoture."C 70
Fig. 6. T e m p e r a t u r e d e p e n d e n c e of t h e s t o r a g e moduli G ' [ d y n cm -2] (o), of t h e l o s s moduli G" ( [ d y n cm -2] (o) a n d of t h e r a t i o G"/G' (Q) f o r m i x t u r e s o f c o n c e n t r a t e d s o l u t i o n s o f i-PMMA (I = 93%) a n d s-PMMA (S = 72%; H : 28%) in o - x y l e n e (mixing r a t i o r = 1.25) (ref. 88). a maximum s h i f t e d t o w a r d s h i g h e r t e m p e r a t u r e s a s c o m p a r e d to n o n a n n e a l e d samples; Feitsma etal.
( r e f . 90) c o n s i d e r t h i s a s i n d i c a t i o n of s t e r e o c o m p l e x
f o r m a t i o n in bulk.
2. D i e l e c t r i c m e a s u r e m e n t s a n d m e a s u r e m e n t s of t h e r m a l l y s t i m u l a t e d depolarization currents.
The monomer u n i t of PMMA h a s a p e r m a n e n t d i p o l e
moment ( p o l a r e s t e r g r o u p ) a n d t h e mean v a l u e of t h e d i p o l e moment of t h e whole m a c r o m o l e c u l e d e p e n d s on i t s c o n f i g u r a t i o n a n d c o n f o r m a t i o n ; in s t u d i e s of s o l u t i o n s o f s t e r e o r e g u l a r pMIV[A in t o l u e n e (conc. 1-5%), t h i s h a s made p o s s i b l e t h e a p p l i c a t i o n o f m e a s u r e m e n t s o f t h e t e m p e r a t u r e d e p e n d e n c e of b o t h c o m p o n e n t s (~',~") of t h e complex d i e l e c t r i c c o n s t a n t ( r e f . 52).
The
f o r m a t i o n a n d d e c o m p o s i t i o n o f t h e s t e r e o c o m p l e x in t h e t e m p e r a t u r e r a n g e 20 -
90"C is m a n i f e s t e d b y a c o n s i d e r a b l e time d e p e n d e n c e o f t h e m e a s u r e d
values and by t h e i r d e p e n d e n c e on the thermal h i s t o r y .
Similar e f f e c t s
i n d i c a t i n g a s s o c i a t i o n h a v e b e e n d e t e c t e d a l s o w i t h s o l u t i o n s of at-PMMA. I n t h e a p p l i c a t i o n of t h e m e t h o d of t h e r m a l l y s t i m u l a t e d d e p o l a r i z a t i o n c u r r e n t s , p e a k s a r e d e t e c t e d c o n n e c t e d w i t h t h e d e p o l a r i z a t i o n of o r i e n t e d -CO0 d i p o l e s in c o n s e q u e n c e of t h e t h e r m a l motion.
Measurements performed
102 with solid films o b t a i n e d b y p r e c i p i t a t i o n f r o m a m i x t u r e of s o l u t i o n s of i a n d s-PMMA in a c e t o n e h a v e r e v e a l e d a p e a k at 105 - 130°C, a s s i g n e d b y t h e a u t h o r s to Tg in t h e s t e r e o c o m p l e x (ref. 86,87).
With films i s o l a t e d d i r e c t l y
from t h e m i x t u r e s of b o t h s o l u t i o n s a t t h e r a t i o i / s -- I / l , a n a d d i t i o n a l p e a k was d e t e c t e d w h i c h c o r r e s p o n d e d to Tg of f r e e i-PMMA, s u g g e s t i n g c o n c l u s i o n s a b o u t t h e s t o i c h i o m e t r y of t h e s t e r e o c o m p l e x .
Only a p a r t of t h e
s t e r e o c o m p l e x a g g r e g a t e s p r e c i p i t a t e s from a c e t o n e solution; t h e o t h e r p a r t of t h e a g g r e g a t e s r e m a i n s in s o l u t i o n a n d a p p e a r s a s " d i s s o l v e d " ( r e f . 87). 3. DSC. By m e a n s of DSC, t h e m e l t i n g e n d o t h e r m of t h e c r y s t a l l i n e p a r t of t h e s t e r e o c o m p l e x was d e t e c t e d in solid s a m p l e s a n d a t t e n t i o n h a s also b e e n p a i d to t h e m e a s u r e m e n t of t h e g l a s s t r a n s i t i o n t e m p e r a t u r e ( r e f . 35).
For
solid s t e r e o c o m p l e x s a m p l e s o b t a i n e d b y p r e c i p i t a t i o n from s o l u t i o n , t h e e x i s t e n c e of two m e l t i n g e n d o t h e r m s a t =185"C a n d 210°C was d e e t e c t e d ( r e f . 50).
With t h e s t e r e o c o m p l e x p r e p a r e d in b u l k ( a f t e r p r o l o n g e d a n n e a l i n g of
t h e m i x t u r e of i- a n d s-PMMA a t 140°C), o n e m e l t i n g e n d o t h e r m at ~190"C was o b s e r v e d (two e n d o t h e r m s w e r e o n l y o b s e r v e d a t lower c r y s t a l l i z a t i o n t e m p e r a t u r e ) ( r e f . 90).
The a r e a of t h i s e n d o t h e r m d e p e n d s on t e m p e r a t u r e
a n d time of a n n e a l i n g a n d o n t h e r a t i o ( i / s ) in t h e mixture; t h e m e l t i n g p o i n t t e m p e r a t u r e d o e s n o t d e p e n d on ( i / s ) .
The d o u b l e m e l t i n g e n d o t h e r m ,
o r i g i n a l l y a s s i g n e d to t h e c r y s t a l s of s-PMMA a n d to t h e s t e r e o c o m p l e x ( r e f . 50)~ p r o b a b l y c o r r e s p o n d s o n l y to t h e s t e r e o c o m p l e x i t s e l f , p o s s i b l y a s a c o n s e q u e n c e of p r i m a r y a n d s e c o n d a r y c r y s t a l l i z a t i o n ( r e f . 37).
Katime e t al.
( r e f . 51,96) a s s i g n t h e h i g h - t e m p e r a t u r e e n d o t h e r m to t h e s t e r e o c o m p l e x i t s e l f a n d t h e l o w - t e m p e r a t u r e e n d o t h e r m to a g g r e g a t e s stereocomplex.
( c l u s t e r s ) of t h e
B l e n d s of i - a n d at-PMMA p r e p a r e d f r o m a c e t o n e s o l u t i o n
e x h i b i t o n e b r o a d m e l t i n g e n d o t h e r m a r o u n d 150"C ( r e f . 98).
M e a s u r e m e n t s of
Tg i n d i c a t e t h a t b o t h i - p o l y ( e t h y l m e t h a c r y l a t e ) (PEMA) a n d s - p o l y ( i s o b u t y l m e t h a c r y l a t e ) (PiBMA) form c o m p a t i b l e m i x t u r e s in t h e solid s t a t e , p r o b a b l y a s a c o n s e q u e n c e of s t e r e o c o m p l e x f o r m a t i o n in b u l k , with a m e l t i n g e n d o t h e r m a t 153"C (ref. 94). The m e l t i n g e n d o t h e r m was also d e t e c t e d in g e l s f o r m e d b y mixing of c o n c e n t r a t e d s o l u t i o n s of i - a n d s-PMMA in o - x y l e n e (conc. 20% a n d h i g h e r ) (ref. 91,95,97).
It was f o u n d t h a t c r y s t a l l i z a t i o n a n d n u c l e a t i o n in g e l s of
s-PMMA a n d in t h e s t e r e o c o m p l e x is b y s e v e r a l o r d e r s more r a p i d t h a n in i-PMMA.
Consequently, s - P M M A
and the stereocomplex crystallize even
without annealing, which in this case only affects the size distribution of crystals.
T h e similarity in the crystallization behavior of s - P M M A
a n d of the
stereocomplex is considered to be based on the circumstance that in both cases the crystallization behavior is affected b y the short lengths of s-sequences
(ref. 95). T h e quantitative determinations of the heat of melting
103 in PMMA g e l s c a n be c o m p l i c a t e d b y t h e o v e r l a p p i n g v a p o r i z a t i o n of t h e s o l v e n t .
e f f e c t of t h e h e a t of
F r o m t h e m e a s u r e d v a l u e s of t h e h e a t of m e l t i n g
a n d t h e d e g r e e of c r y s t a l l i n i t y , t h e e n t h a l p y of PhIMA s t e r e o c o m p l e x f o r m a t i o n was determined
(AH = - 2 4 J / g )
( r e f . 97); t h i s v a l u e is i n g o o d a g r e e m e n t w i t h
t h e v a l u e s o b t a i n e d b y m i x i n g c a l o r i m e t r y in s t u d i e s of d i l u t e s o l u t i o n s (ref. 93,99). 4. X - r a y d i f f r a c t i o n . T h e f i r s t s t u d i e s of t h e PMMA s t e r e o c o m p l e x h a v e a l r e a d y s h o w n t h a t t h e g e l s f o r m e d b y m i x i n g of c o n c e n t r a t e d a n d s-PMMA in DMF e x h i b i t a c r y s t a l l i n e X - r a y p a t t e r n t h a t f o u n d f o r t h e s o c a l l e d s t e r e o b l o c k ( r e f . 1,83). pattern
s o l u t i o n s of i -
of t h e s a m e t y p e a s
T h e s a m e t y p e of X - r a y
w a s f o u n d a l s o f o r t h e s t e r e o c o m p l e x g e l s in b e n z e n e a n d f o r solid
s a m p l e s of t h e s t e r e o c o m p l e x ( a f t e r r e m o v a l of s o l v e n t ) i s o l a t e d f r o m a c e t o n e , a c e t o n i t r i l e , b e n z e n e a n d o - x y l e n e s o l u t i o n ( r e f . 59,69,95).
The same
d i f f r a c t o g r a m a s t h a t Of t h e s t e r e o c o m p l e x i s o l a t e d f r o m a c t o n e s o l u t i o n w a s a l s o f o u n d f o r t h e s t e r e o c o m p l e x in b u l k o b t a i n e d b y p r o l o n g e d a n n e a l i n g of t h e m i x t u r e of i - a n d s-PMMA ( w i t h o u t s o l v e n t ) a t 140"C ( r e f . 90).
The
v a l u e s of t h e c r y s t a l l i n i t y of t h e solid s t e r e o c o m p l e x i s o l a t e d f r o m DMF o r o - x y l e n e s o l u t i o n d e p e n d o n t h e m o d e of p r e p a r a t i o n 30%9 r e s p e c t i v e l y , a t m o s t ( r e f . 50,97).
a n d a m o u n t to 40 a n d
These results prove that the
f o r m a t i o n of t h e s t e r e o c o m p l e x i s a t l e a s t p a r t l y c o n n e c t e d w i t h t h e c r y s t a l l i z a t i o n of s e g m e n t s of PMMA c h a i n s . concentrated
s o l u t i o n s of i - a n d s-PMMA in DMF, o r i e n t e d f i b e r s of t h e
stereocomplex have also been prepared the X-ray fiber patterns = 2/1 to 1/2).
( r e f . 33,37,100).
of
L i q u o r i e t al. ( r e f . 33), o n t h e b a s i s of t h e f i b e r
h o w e v e r , some d o u b t s
model of t h e PMMA s t e r e o c o m p l e x ;
have arisen concerning
t h e o r i g i n of t h e r e f l e c t i o n s
to t h e s y d i o t a c t i c c o m p o n e n t ( r e f . 41).
stereocomplex was recently proposed energy
The appearance
d o e s n o t d e p e n d o n t h e r a t i o ( i / s ) (in t h e r a n g e i / s
diffractogram, have proposed a structural
assigned
F r o m t h e g e l s of m i x t u r e s of
A r e v i s e d model of t h e PMMA
based on X-ray diffraction and potential
c a l c u l a t i o n s ( r e f . 100).
Q u i t e r e c e n t l y , it h a s b e e n s h o w n b y X - r a y d i f f r a c t i o n t h a t s-PMMA i s p a r t l y c r y s t a l l i n e o n l y in t h o s e c a s e s w h e n it is i s o l a t e d f r o m a s o l u t i o n w h e r e it h a s b e e n p r e s e n t
in the a g g r e g a t e d
c r y s t a l l i n i t y of s-PMMA p r e p a r e d temperature
s t a t e ( r e f . 22,102).
The
b y e v a p o r a t i o n of s o l v e n t a t r o o m
f r o m o - d i c h l o r o b e n z e n e , t o l u e n e , BACj d i e t h y l k e t o n e o r o - x y l e n e
s o l u t i o n a m o u n t e d to 30-40%; t h e s i z e of t h e c r y s t a l l i t e s w a s 4.6 - 6.5 nm ( r e f . 22,38,95,97,102).
The preparation
of o r i e n t e d f i b e r s of c r y s t a l l i n e
s-PMMA b y a b s o r p t i o n of c h l o r o a c e t o n e o r d i e t h y l k e t o n e v a p o r s 24,100,101) h a s a l s o b e e n d e s c r i b e d .
Intermediate-angle
i n d i c a t e s t h e e x i s t e n c e of s p e c i f i c l o n g - r a n g e s-PMMA ( r e f . 23).
(ref.
X-ray scattering
i n t e r a c t i o n s in a s o l u t i o n of
104 5. E l e c t r o n m i c r o s c o p y . T h i s m e t h o d w a s a p p l i e d in a s t u d y of s-PMMA ( r e f . 22).
A p r i n c i p a l l y d i f f e r e n t m o r p h o l o g y of s-PMMA s a m p l e s i s o l a t e d f r o m
various solvents was observed
w h i c h d e p e n d o n t h e e x i s t e n c e or
n o n - e x i s t e n c e of s e i f - a g g r e g a t i o n e f f e c t of t e m p e r a t u r e
of s-PMMA i n t h e r e s p e c t i v e
solvent.
The
o n t h e s t a b i l i t y of t h e r e s p e c t i v e m o r p h o l o g y w a s
investigated.
C. M e t h o d s of m o l e c u l a r s p e c t r o s c o p y
(NMR s p e c t r o s c o p y , v i b r a t i o n a l
spectroscopy 1. N___MRS p e c t r o s c o p y . spectroscopy
The paragraph
c o n c e r n i n g t h e p o s s i b i l i t i e s of NMR
in s t u d i e s of a g g r e g a t i o n of s t e r e o r e g u l a r
somewhat more detailed t h a n the p r e c e d i n g
PMMA will be
paragraphs,
e x p l a n a t i o n s of t h e b a s i c p o s s i b i l i t i e s of t h i s m e t h o d .
especially in This is c a u s e d by the
c i r c u m s t a n c e t h a t t h i s m e t h o d c a n y i e l d a lot of i n f o r m a t i o n n o t o b t a i n a b l e o t h e r w i s e ; a t t h e s a m e time, t h e a p p l i c a t i o n of NMR s p e c t r s o c o p y
in t h i s f i e l d
is n o t v e r y w i d e s p r e a d to d a t e . T h e a s s o c i a t i o n of s t e r e o r e g u l a r
PMMA { i n c l u d i n g s t e r e o c o m p l e x f o r m a t i o n )
h a s b e e n s t u d i e d b y v a r i o u s t e c h n i q u e s of NMR s p e c t r o s c o p y .
In h i g h
r e s o l u t i o n 1H NMR s p e c t r a , PMMA s t e r e o c o m p l e x f o r m a t i o n i s m a n i f e s t e d b y t h e r e d u c t i o n of i n t e n s i t y of all p o l y m e r b a n d s s o m e c a s e s to a c o m p l e t e d i s a p p e a r a n c e Self-aggregation
( r e f . 65,69,103,104), l e a d i n g i n
of t h e s p e c t r u m
(Fig. 7).
of i - o r s-PMMA is m a n i f e s t e d in h i g h r e s o l u t i o n 1H NMR
s p e c t r a in a s i m i l a r w a y (ref. 2,3,54,109).
Similar b e h a v i o r h a s b e e n o b s e r v e d
a l s o w i t h a n u m b e r of o t h e r a s s o c i a t e d p o l y m e r s y s t e m s ; t h e s e f i n d i n g s a r e b r i e f l y s u m m a r i z e d in r e f . 117.
T h e r e d u c t i o n of i n t e n s i t i e s is e v i d e n t l y
c a u s e d b y a d e c r e a s e of p r o t o n m o b i l i t y i n a s s o c i a t e d s t r u c t u r e s v a l u e s t h a t t h e w i d t h of t h e c o r r e s p o n d i n g hundreds
NMR l i n e s i s of t h e o r d e r of
of Hz o r m o r e , so t h a t t h e s e p r o t o n s e s c a p e d e t e c t i o n in h i g h
r e s o l u t i o n NMR s p e c t r a .
The observed
h i g h r e s o l u t i o n NMR s p e c t r u m
e x a m p l e , Fig. 7b) i n t h e s e s y s t e m s c o r r e s p o n d s units.
to s u c h
(see, for
to n o n - a s s o c i a t e d m o n o m e r
T h e r e f o r e , f r o m t h e d y n a m i c p o i n t of v i e w , t h e NMR s p e c t r a of PMMA
solutions, where aggregation
t a k e s place, can in principle be a n a l y z e d as
two-component systems, with one component corresponding
to a s s o c i a t e d u n i t s
a n d t h e o t h e r to n o n - a s s o c i a t e d u n i t s (ref. 3,103,104). A g g r e g a t i o n c a n b e f o l l o w e d q u a n t i t a t i v e l y f r o m m e a s u r e m e n t s of t h e integrated
i n t e n s i t i e s of h i g h r e s o l u t i o n NMR b a n d s
2,3,38,47,54,102-104,108-110).
The integrated
(ref.
b a n d i n t e n s i t i e s I in s y s t e m s
w h e r e a s s o c i a t i o n o c c u r s a r e g i v e n b y t h e r e l a t i o n ( r e f . 3,118):
I -- K ' N n ( T ) ' ( I / T ) ' a l / 2
(1)
105
I I
6
7
8
9
IE in ppm
F i g . 7. H i g h r e s o l u t i o n 1H NMR s p e c t r a o f s a m p l e s o f PMMA i n C6D 6 a t i d e n t i c a l i n s t r u m e n t s e t t i n g s a n d 27°C" (a) s - P M N A - 1 (S = 8 8 . 5 ~ , H ; 9%}; (b) m i x t u r e i - P N M A (I = 97%, H = 3%) + S - P N M A - 2 (S = 69%, H = 27.5%) (1:2); (c) m i x t u r e i-PMMA + s - P M M A - 1 (1:2) ( r e f . 103). where
K is a constant,
non-associated the absolute without
temperature
association,
analogous
Nn(T) is the temperature-dependent
nuclei in the unit volume contributing
and a is the so called saturation
integrated
band
unit volume which contribute possible
intensities,
to Eq. 1, w i t h N n s u b s t i t u t e d
to d e t e r m i n e
is the number comparison
number
to t h e g i v e n
band.
By means
of associated
T is
In systems
by a relation
b y No, t h e t o t a l n u m b e r
to t h e g i v e n
the fraction
of associated
factor.
Io, a r e g i v e n
of band,
of nuclei in
o f E q . 1, it i s
nuclei, p = Na/N o (where
Na
n u c l e i i n u n i t v o l u m e , No = Na + Nn) b y d i r e c t
of integrated
intensities
at negligible
saturation
(a -~ 1) a n d
temperature,
instrument
settings)
of high
resolution
NMR s p e c t r a
under
identical
conditions
with and
without
association:
measured
{concentration,
p : 1 - I / I o.
(2)
As in aggregation intensities corresponds
can be revealed
decreases
the temperature
dependence
dependence
s - P M M A (of h i g h demonstrating temperature
without
with increasing structures
of the integrated of integrated
of the fraction
stereoregularity)
band
behavior,
the value,
p,
monomer units.
also from the temperature
the decomposition range
of associated
of associated
by an increase
PMMA, t h e i n t e g r a t e d
exhibit identical
While i n s y s t e m s
monotonously
Eq. 1, t h e d e c o m p o s i t i o n
temperature
groups
to t h e f r a c t i o n
intensities.
will b e s h o w n
of stereoregular
proton
directly
Association integrated intensity
studies
of various
dependence
association temperature,
according
with increasing intensity
intensity
and
I.
of
the integrated to
temperature
As an example,
the corresponding
p for a mixture of solutions
of i- and
i n D M F - d 7 i s s h o w n i n F i g . 8, (melting) of stereocomplex
50 - 120"C ( s e e r e f . 105).
aggregates
in the
106
i
50
8 O o
c r-
nt~
)
-60
I
40 30 20
201 Fig. 8. T e m p e r a t u r e IH NMR s p e c t r a (o) m i x t u r e s o f i-PMMA m i x i n g r a t i o r -- 1.2
I
I
50
100
\
-
- 150 t e m p e r e t u r e , "C
d e p e n d e n c e of the i n t e g r a t e d i n t e n s i t y in h i g h r e s o l u t i o n a n d f r a c t i o n of a g g r e g a t e d m o n o m e r u n i t s p (e) f o r (I = 91%; H -- 7%) a n d s-PMMA (S = 85%; H = 12%) w i t h i n DMF-d 7.
By m e a n s o f t h e v a l u e s of t h e a s s o c i a t e d
fraction
followed.
I n t h i s w a y , t h e e f f e c t of s o l v e n t , r a t i o ( i / s ) , s t e r e o r e g u l a r i t y ,
studied found
factors
from high
IH NbIR s p e c t r a ,
and thermal history
the effect of various
p determined
resolution
on association can be
o n t h e f o r m a t i o n o f PMMA s t e r e o c o m p l e x a g g r e g a t e s
and their thermal stability was characterized
( r e f . 103,104).
t h a t i n t h i s c a s e t h e v a l u e s of p a r e p r a c t i c a l l y
independent
molecular weight
(if t h i s is h i g h e r
relatively weakly dependent
than a certain
on concentration
time was
It was of
limit) ( r e f . 103) a n d
( r e f . 119). T h u s , i d e n t i c a l v a l u e s
of p w e r e f o u n d
f o r m i x t u r e s o f i - a n d s-PMMA i n C6D6, w i t h a
number-average
m o l e c u l a r w e i g h t o f s-PMMA e q u a l t o 44000 in o n e c a s e a n d
t o 2600 i n a n o t h e r
(stereoregularity
of b o t h s-PMMA s a m p l e s w a s i d e n t i c a l ) .
A weak effect of molecular weight was also p rove d self-aggregatior/.
While f o r a n o - d i c h l o r o b e n z e n e
65%; H = 31%; I = 4%) of ~ stereoregularity
i n t h e c a s e o f s-PMMA s o l u t i o n o f at-PMMA (S =
= 45,000, p = 0, f o r at-PMMA of t h e s a m e
b u t m o l e c u l a r w e i g h t of a b o u t o n e million, in t h e s a m e
s o l v e n t p : 9% ( r e f . l l 9 ) .
The effect of conce ntra tion
detail for mixtures of i- and
was studied
s-PMMA i n t o l u e n e - d 8 ( r e f . I 1 9 ) .
in g r e a t e r
Although the
v a l u e s o f p f o r c = 0.2% (p =76%) a r e l o w e r t h a n f o r c = 10% (p : 93%), it i s
107 e v i d e n t t h a t e v e n in f a i r l y d i l u t e s o l u t i o n s t h e i - a n d s - P M M A in m u t u a l i n t e r a c t i o n .
concentration and stereoregularity also characterized determined
on s e l f - a g g r e g a t i o n
( r e f . 2,3,38,47,54,102,109,110).
(ref. 38,54).
was
By m e a n s of NMR s p e c t r o s c o p y ,
the
f o r m a t i o n in t o l u e n e - d 8 a n d in BAC w a s a l s o
M e a s u r e m e n t s of the i n t e g r a t e d
r e s o l u t i o n 1H NMR s p e c t r a w e r e u s e d to c h a r a c t e r i z e the diner
of i - o r s-PMMA w a s
a n d t h e t h e r m a l s t a b i l i t y of t h e s e l f - a g g r e g a t e s
k i n e t i c s of s-NMMA s e l f - a g g r e g e studied
molecules are
By m e a s u r e m e n t o f t h e p - v a l u e s , t h e e f f e c t of s o l v e n t ,
model of PMMA, t h e d i m e t h y l e s t e r of
i n t e n s i t i e s of h i g h the interaction between
2,2,4,4-tetramethylglutaric
a c i d (DMTMGA) a n d i - o r s-PMMA (ref. 108). B e s i d e s t h e v a l u e s of p, b a s e d o n d i r e c t m e a s u r e m e n t of t h e s i g n a l of non-associated units, further d y n a m i c s of a g g r e g a t e d aggregated
information concerning the structure
and
s e g m e n t s c a n be o b t a i n e d b y t h e m e a s u r e m e n t of t h e
c o m p o n e n t b y b r o a d - l i n e NMR s p e c t r a , t h e m e a s u r e m e n t of
non-selective relaxation times with a pulse spectrometer and by the a p p l i c a t i o n of the t e c h n i q u e s of m e a s u r e m e n t of s o l i d - s t a t e h i g h r e s o l u t i o n spectra.
I n o u r s t u d i e s of t h e a s s o c i a t i o n of s t e r e o r e g u l a r
we h a v e u s e d two s u c h m e t h o d s ; i.e., 1H NMR s p e c t r a magic-angle spinning
(MAS) a n d 13C NMR s p e c t r a
p r o t o n d e c o u p l i n g (ref. 104,106,110).
m e a s u r e d with s t r o n g
W h e n t h e b r o a d e n i n g of b a n d s of n u c l e i
in a s s o c i a t e d s e g m e n t s is c a u s e d b y n e a r - s t a t i c the spinning frequency
PMMA i n s o l u t i o n ,
measured with
dipolar interactions and when
v r in 1H NMR s p e c t r a o r t h e i n t e n s i t y of t h e
d e c o u p l i n g field YH2/2~ i s s u f f i c i e n t l y h i g h { l a r g e r t h a n t h e w i d t h of t h e p r o t o n b a n d i n t h e c o n v e n t i o n a l l y m e a s u r e d s p e c t r u m ) , a p p l i c a t i o n of t h e s e t e c h n i q u e s c a n l e a d to t h e n a r r o w i n g of t h e b r o a d b a n d of t h e a s s o c i a t e d s e g m e n t s a n d to t h e a p p e a r a n c e
of a h i g h r e s o l u t i o n NMR s p e c t r u m .
Thus,
a l r e a d y t h e s i m p l e s t a t e m e n t a b o u t t h e e f f e c t i v e n e s s of t h e s e t e c h n i q u e s contributes
to t h e c h a r a c t e r i z a t i o n of n o t i o n a l h i n d r a n c e in t h e a s s o c i a t e d
s e g m e n t s { p r e s e n c e o r a b s e n c e of n e a r - s t a t i c In stereocomplex gels generated of h i g h s t e r e o r e g u l a r i t y
dipolar interactions).
b y m i x i n g o f s o l u t i o n s o f i - a n d s-PMMA
a n d i n s-PMMA s e l f - a g g r e g a t e s
in t o l u e n e - d s , the
b r o a d e n i n g of b a n d s of a s s o c i a t e d s e g m e n t s i s n o t c a u s e d b y n e a r - s t a t i c dipolar interactions~ but by the reduced
v e l o c i t y of t h e e f f e c t i v e l y i s o t r o p i c
m o t i o n of t h e m a i n c h a i n ( r e f . 106,110).
In this respect, these systems
q u a l i t a t i v e l y d i f f e r from the swollen gels of chemically c r o s s l i n k e d p o l y m e r s where large linewidths are connected with rapid internal motions restricted s p a c e ( r e f . 120); in c h e m i c a l l y c r o s s l i n k e d g e l s , t h e s p a t i a l r e s t r i c t i o n of m o t i o n of m o s t m o n o m e r u n i t s i s a c o n s e q u e n c e of t h e e x i s t e n c e of a r e l a t i v e l y s m a l l n u m b e r of s t a t i c e r o s s l i n k p o i n t s .
The observed
different
b e h a v i o r i n d i c a t e s t h a t i n t h e f o r m a t i o n o f t h e PMMA s t e r e o c o m p l e x a n d in self-aggregation
of s-PMMA a d i r e c t c o n t a c t of l o n g c h a i n s e g m e n t s t a k e s
in
108 place and
that
the number
considerable. the fraction fraction
NMR s p e c t r o s c o p y stereocomplex,
(i/s).
segments
with other
In connection
formation,
the relaxation
Overhauser
factors,
structure
o f PMMA ( r e f . 29).
relaxation
p on
and in
measured
by the
differences
alone; the same is true
were
shape
for
o f 13C T 1 with cross
( r e f . 107).
as compared
the general
measured
the effect of solvent
13C MAS NMR t e c h n i q u e
were observed
concerning
t i m e s T 1 o f 1H
The values
(CP) f o r t h e s o l i d PMMA s t e r e o c o m p l e x
no remarkable
p in
of the fraction
associated
s-PMMA with the aim of determining
times were
observations,
o f NMR s p e c t r o s c o p y
on the conformational
polarization
of the
o f IR a n d
methods.
with stereocomplex
of i- and
measure
of the fraction
dependence between
advantage
13C n u c l e i , a s w e l l a s t h e n u c l e a r
solutions
i n Eq. 2 a s
In the case of the
by further trends
the sharp
is a great
a realistic
VI-A).
of the temperature and
is
p defined
(see also comparison
is also supported
T h e a b i l i t y to d i f f e r e n t i a t e
non-associated comparison
represent
contact
in the following text, Part
this conclusion
monomer units
of the fraction
thus
in direct
on stereoregularity
the ratio
and
units
by the character
depedence
interacting
high values
of the less mobile units
of associated
especially
of mutually
The observed
In this case,
to i - a n d of the
s-PMMA
13C CP MAS NMR
spectra.
2. I n f r a r e d suitable
(IR) a n d
method
the given
Raman sDectroscopy.
for studies
case for the detection
consequence
of association.
aggregation
of stereoregular
in studies
of solid samples
has shown
that
stereocomplex intensity
assigned
the shape
Various
and
intensity
bands
The authors
the dynamics
methyl
of the ester
the intensities
of the doublet
conformational
structure
formation manifested
by an increase
tendency
remains
situation
is illustrated
preserved
vibrations
o f t h e PMMA
that
changes
and
they
resemble
in terms
attention
to t h e
that
the is
even
in the solid state
a t 860 cm - 1 a n d
(ref. 21,22,113).
the spectra
of
w a s p a i d to
sensitive
It was observed
of the band
(ref.
(~1450 cm - 1 )
from the shape
these
and
studied.
as well as of the s-PMMA aggregates,
of the intensity
in
of
solutions
were
860 c m - 1 w h i c h a r e
i n F i g . 9, w h i c h e x h i b i t s
s o l i d PMMA s t e r e o c o m p l e x
bands
Considerable
o f s - P M M A ( r e f . 21).
of the stereocomplex,
group
of at-PMMA but
interpret
a t 843 a n d
from these
o f IR s p e c t r a
of these
group.
in
structure
both in studies
considerably
i n CC14 s o l u t i o n s
s o l i d a t - P M M A ( r e f . 114).
is a
of polymers,
(ref. 21,22,102,111,114,116}
methyl
i n CC14 ( c o n c . 1%) d i f f e r
of these
used
isolated
ranges
to t h e e s t e r
spectroscopy
structure
of conformational
were
PMMA i n s o l u t i o n
of the structure
of bands
of changes
IR s p e c t r a
21,22,101,102,111-113,115,116}. Analysis
Vibrational
of the conformational
this
This
of s-PMMA in the
(A), o f s - P M M A i n N u j o l m u l l (B) a n d o f s - P M M A
109 films isolated or does
stereocomplex change
from media where
{D,E) t a k e
place.
formation
two different
for the conformational addition
to t h e a b o v e
manifested carbonyl
and
especially stretching
structure
by the appearance
22,102,111).
This ordering
polymerization measurements stability
is preserved
aggregation
takes
place
in aggregation-promoting of the temperature
solid s-PMMA was characterized conformational
structure
with a
Based on measurements r e f . 21,22) w e r e
of new bands
groups
in t h e r a n g e
of
(ref. from
(ref. 22,102,111) or prepared
and
( r e f . 21,22).
of s-PMMA in solution
( r e f . 115).
o f IR s p e c t r a , of the ordered
is
in
in the aggregates
in solid s-PMMA isolated
dependences
proposed
In
1727 c m - 1 ( w e a k )
solvents
o f t h e s o l i d PMMA s t e r e o c o m p l e x
both
of s-PMMA in solution
a t 1742 cm - 1 a n d of ester
that
in the stereocomplex.
self-aggregation
vibrations
d o e s n o t (C)
indicate
are connected
of s-chains.
of s-chains
changes,
of mutual ordering
where
shown
m o d e l s {cf. r e f . 113 a n d
structure
consequence
solutions
of the polymer
which are
s-PMMA self-aggregation
of the conformational
o f IR s p e c t r a ,
self-aggregation
The changes
by
From the thermal structures
The effect of solvent was also studied
in
on the
( r e f . 21,22,29).
E
o
.o
!
g00
850
cm-1 800
Fig. 9. Part of IR spectrum of B-PMMA (S : 89.5%; H : 8.5%) films. Spectrum of s-PMMA in film of PMMA stereocomplex (i.e., normalized difference of
spectra of stereocomplex and i-PMMA) (A) and of B - P M M A in Nujol mull (B); spectra of s - P M M A films prepared by evaporation of solvent from s - P M M A in acetonitrile (C), o-dichlorobenzene (D) and toluene (E) at 25"C. All spectra measured at 25"C (ref. 22).
110
T h e solid PMMA s t e r e o c o m p l e x w a s a l s o s t u d i e d b y R a m a n s p e c t r a 21).
(ref.
Also b y t h i s m e t h o d , it w a s f o u n d t h a t t h e i n t e n s i t i e s of t h e b a n d s of
t h e s t e r e o c o m p l e x a r e n o t a n a d d i t i v e s u m of t h e i n t e n s i t i e s of t h e i - a n d s-components.
Raman spectroscopy
has also contributed
t h e o r i g i n of t h e s p l i t t i n g of t h e c a r b o n y l s t r e t c h i n g d i p o l e c o u p l i n g of e s t e r g r o u p s ) i n o r d e r e d
V.
FORMATION
AND CHARACTER
d e p e n d s on a n u m b e r
vibration (transition
s e q u e n c e s of s-PMMA (ref. l l l ) .
OF AGGREGATES
T h e formation and character of P M M A
to t h e e x p l a n a t i o n of
OF PMMA
stereocomplex aggregates in solution
of factors; e.g.: I) on the ratio i/s in the mixture; 2)
on the degree of stereoregularity of the components; 3) on temperature; 4) on the time from the mixing of the components; 5) on thermal history; a n d 6) on solvent.
If w e exclude the ratio i/s in the mixture, then the same factors
also affect self-aggregation of s - P M M A .
In the following text, the effects of
each of these factors will be discussed separately.
However, it has to be
kept in mind that in reality all these factors act as a complex and it m a y cause some difficulties to separate their effects.
After the paragraph
devoted to the question of the stoichiometry of the stereocomplex, all three forms of aggregation of stereoregular P M M A self-aggregates of i- and s - P M M A )
(i.e., stereocomplex and
will be discussed in parallel in the
following p a r a g r a p h s in order to stress the similarities a n d also the differences existing between these three forms. A. Stoichiometry of P M M A A large n u m b e r
stereocomplex
of papers (often presenting very differing views) were
devoted to the problem of the stoichiometry of the stereocomplex. Chiang eL al. (ref. 40) (based on sedimentation measurements)
While
conclude that
no defined stoichiometry of the stereocomplex exists, other authors a s s u m e parallel existence of sterecomplexes of the composition i/s = 2/1, i/I a n d 1/2 (ref. 34,41), while the remaining papers advocate stereocomplex formation at a given ratio i/s. Most papers find the stoiehiometry i/s = 1/2 (ref. 33,35,37,39,48,56,65,86,87,92) but papers indicating the stoichiometry i/s = i/I also exist (ref. 49,50,59,60,66,70).
At the same time, the possibility of
stereocomplex formation in the ratio i/s = 1/2 is also not excluded, assuming its generation from the primary complex with i/s = I/I in the presence of free s - P M M A
in the system (ref. 49,50,59).
T h e values cited above of the
ratio i/s refer to the weight ratio of both c o m p o n e n t s and not to the ratio of chains (sequences) in mutual interaction.
Therefore, there is no reason w h y
the stoichiometric ratio should be given only b y whole n u m b e r s I/2.
T h e results of N M R
as I/I or
spectroscopy a n d mixing calorimetry indicate i/s =
1/1.5 (ref. 103) a n d intermediate between i/s = 1/1.5 to I/2 (ref. 93), respectively.
111 The contradictory results concerning the stoichiometry of the stereocomplex
can have a number
of reasons
and
some of these
we s h o u l d
l i k e to p o i n t o u t n o w : (i) I n o u r o p i n i o n , a n u m b e r imperfect
stereoregularity
is not specified stereocomplex interactions depends
evident quantity
quantities authors
where
turbidity,
molecular
( r e f . 66,93} t r y
weight)
attains
Similar difficulties
contains
short
may appear
sequences
radical
polymerized
s-triads.
the weight
However, even
PMMA.
stereoregularity
this procedure
on the example of conventional
triads
it c a n n o t
in stereospecific
(units
marked
be excluded
interaction
component
by an asterisk that
even
respectively).
to u s e s a m p l e s
of i- and
certainly
in only several
higher
papers
the weight
s-PMMA in stereocomplex 90%; h o w e v e r ,
associated sequences
f .J.
LDLDLDL IDDDDLDLDIDLDLD IDL - s-PMMA DDD DDD
IDDDD_ I_PMMA
studies
participate
( r e f . 103) t h a t
the
to i s o t a c t i c
fractions
these
this condition
(ref. 34,35,37,50,56,65,103).
.I. .l.
below).
in t h e s c h e m e ) .
indicate compared
T h e o n l y w a y to e x c l u d e
than
scheme
can directly
m a x i m u m to a h i g h e r
Xi a n d Ys a r e
If the
r a t i o , we e l i m i n a t e t h e
suggested
component
l e a d s to a s h i f t o f t h e a s s o c i a t i o n
s-components,
units
as
PMMA (S ~
are present.
in our
these
o f NMR s p e c t r o s c o p y
of syndiotactic
m i x i n g r a t i o r (r : Y s / X i , w h e r e
tacticity,
for the weight
(e.g., in the manner
At t h e s a m e t i m e , t h e r e s u l t s lower stereoregularity
sequences
by
is problematic
only short
is substituted
Some
ratio of both components
practically
s-triads
also in
in non-negligible
to e l i m i n a t e t h e e f f e c t o f i n s u f f i c i e n t
PMMA b y r e p l a c i n g
a minimum or
specifically
heterotactic
it is
ratio of i- and
60%; H -- 30%), w h e r e
However,
which
contain
can be demonstrated
ratio of i- and
text,
one, then
to t h e s t o i c h i o m e t r i c
as is the case in conventional
the ratio of i- and
minimum length
to t h e p r e d o m i n a t i n g
sequences.
the polymer
of the interacting
in further
of intermolecular
If one or both components
opposite
not correspond
in the associated cases
a certain
by
ratio of i- or s-PMMA in the mixture at which some
(e.g., viscosity, need
can be caused
which in some papers
A s will b e s h o w n
than
of solvent.
the weight
results
polymers
place in consequence
longer
of configuration
maximum value
those
takes
of sequences
that
s-units
a t all ( r e f . 33,39,40).
formation
on the type
sequences
of contradictory
of the interacting
value of of i- and
complications
of possibly has been
is
highest fulfilled
112 (ii) S o m e a u t h o r s where
assume
the measured
the stoichiometry
quantity
reaches
33,48).
Mixtures
studied
a t all ( r e f . 3 5 , 6 0 , 6 5 , 8 7 ) .
quantity
with values
in dependence
distinction
between
i/s = 1/2 even
in those
cases
a m a x i m u m a t t h e r a t i o r = 1.5 ( r e f .
of r between
r = 1 to 2 w e r e
The observed
extreme
o n Ys s o m e t i m e s i s n o t s h a r p
the stoichiometries
i/s
sometimes
not
of the measured enough
to permit
= 1.5 o r 1 / 2 { r e f .
33,35,39,50,56,70,92). (iii) T h e o b s e r v e d that
differences
in some methods
measured
quantity
participating
is not directly
in stereocomplex
r need
not signify
ratio.
In other
differing
values
observed
that
that
various
quantities
Actually,
Kusakov
anisotropy t o r = 1. to other
associated
(p) a n d
differentiation
and
the components. spectra
of mixtures values
shown
determination
by the measurement
of solutions
of highly
of the stereocomplex
of solutions
i n F i g . 10.
of i- and
A comparison
a t r = 2, t h e m i n i m u m
of the stoichiometry
of the
of the
in the mixture; and
of the extent
of the ratio of components
at somewhat
( r e f . 60) h a v e
1) d i f f e r e n t i a t i o n
fractions
in this
of the aggregates
s-PMMA in the non-associated
Therefore,
various
stoichiometry
thus
in studies
(l-p)
extremes
Mekenitskaya are formed
make possible:
at some value
is stoichiometric
maximum ordering
used
non-associated
of i- and
chemical shifts)
mixtures
methods
1H NMR s p e c t r a
etc., the
of units
observed
could exhibit and
aggregates
indicating
to t h e n u m b e r
stereocomplex
of r.
of segmental
light scattering,
An extreme
words,
corresponds Contrary
proportional
heaviest
by the circumstances
turbidimetry,
formation.
the associated
while the
stereocomplex,
can also be caused
like viscometry,
part
stereoregular
(by differing
of association
of high
resolution i- and
can be obtained
( r e f . 103).
of lines corresponding
L
L
I
I
6
'7
8
9
of each of 1H NMR
s-PMMA at
r, reliable information
s - P M M A i n C6D 6 a t v a r i o u s
2)
on the Spectra
of
values
of r are
to i- and
s-PMMA
J
10 -r in ppm
F i g . 10. H i g h r e s o l u t i o n 1H NMR s p e c t r a o f m i x t u r e s o f s o l u t i o n s o f i-PMMA (I = 97%, H = 3%) a n d S - P M M A (S = 88.5%, H = 9%) i n C6D 6 w i t h m i x i n g r a t i o r = l(a), r = 1.5(b), r = 2(c). T h e s p e c t r a w e r e m e a s u r e d a t 27"C a l o n g t i m e after the mixing of both components, with identical instrument setting (ref. 103).
113 indicates
that
corresponds high
for r = 1 the residual predominantly
resolution
spectrum ratio.
NMR s p e c t r u m
of the mixture
high
resolution
to n o n - a s s o c i a t e d
NMR s p e c t r u m
i-PMMA; a t r = 2, t h e r e s i d u a l
is predominantly
that
w i t h r = 1.5 c o r r e s p o n d s
of s-PMMA.
At t h e s a m e t i m e , t h e t o t a l v a l u e o f p i s h i g h e s t
a t r = 2, p = 85%; w h e r e a s
a t r = 1, p = 75%.
also for mixtures
s - P M M A i n CD3CN, w h e r e
of i- and
spectrum
f o r r = 1 (p : 85%) c o r r e s p o n d s
67%} a n d
r = 4 ( p : 48%) o n l y to s - P M M A .
1 a large
part
confirmed currents
o f i-PMMA e x i s t s
also by measurements
stereocomplex
high
resolution
indicates
that
are always i/s
part
in mixtures
of mixing where units
the measured
incorporated
composition methods,
lies between
The formation
individual
high
used
is i/s
to t h e n u m b e r
that
only a very
mainly by the distribution
of
the stereocomplex
in associated
of the degree
i- and
both
has s-sequences
extreme
of a~gregates
of stereoregularity
of the
For the s-component, ( r e f . 103).
o f i-PMMA (I = 97%, H : 3%, S = 0) o f components
i n T a b l e 2.
table, it is evident
increases
considerably
All t h e s y n d i o t a c t i c
of ieotactic
of the syndiotactic
of different
From this
monomer units
of s-PMMA.
small number
of
o f 1H NMR s p e c t r o s c o p y
with syndiotactic
of associated
values}.
of quantitative
of stereo-association.
mixtures
of
the
of various
by means of the interaction
by the application
stereoregularity
that
= 1/2.
to t h e i m p o r t a n c e
i n C6D 6 a r e g i v e n
segments
of the heats
only one type
i/s = 1/1.5 to 1/2 (including
of p for several
i n C6D 6 t h e c o n t e n t
contain
that
to s u m m a r i z e
in studies
stereoregularity
with increasing
proportional
By a combination
its stoichiometry
of the effect
stereoregularities that
= 1.5 to 1 / 2 .
points
was solved
The values
from measurements
is roughly
of the stereocomplex
components
this problem
p values,
r, the associated
of stereoregularity on the formation of a~re~ated sequences}
sequences
characterization
method,
with the ratio of units
in the interval
stereoregular
i/s
it is possible
B. E f f e c t o f d e g r e e (minimum length
very
and
stoichiometry,
somewhere
The composition
from the residual
with the ratio of monomer units
e t al. ( r e f . 37) c o n f i r m
exists
It seems that unique
of a primary
i n t h e c o m p l e x , B i r o ~ e t al. ( r e f . 93) c o n c l u d e
Vorenkamp
stereocomplex
(cf, r e f . 4 9 , 5 0 , 5 9 ) .
composition
with r =
depolarization
the existence
as determined
s-sequences
value
NMR
was recently
with the corresponding
of different
By a further
resolution
in mixtures
state
stimulated
against
= 1/1
together
of i- and
= 1 / 1 . 5 ( r e f . 103}.
The fact that
of the mixture,
NMR s p e c t r u m
composed
argues i/s
were observed
the high
to o n l y i-PMMA, f o r r = 2.5 (p =
of thermally
with a composition
of the non-associated
to t h e m i x i n g
a t r = 1.5 (p = 89%};
Similar results
in the non-associated
( r e f . 86,87}; t h i s c l e a r l y
T h e NMR
approximately
triads
sequence
and
polymers
they
lengths.
differ
It can be
114 TABLE 2 F r a c t i o n of a s s o c i a t e d m o n o m e r u n i t s p a n d m i n i m u m l e n g t h s - s e q u e n c e s f o r s o m e m i x t u r e s o f i - a n d s-PMMA in C6D 6
T y p e of s y n d i o t a c t i c
component a
Mixing r a t i o b
p
r = Ys/Xi
s-PMMA
- I
(I = 2.5%; H:9%; S : 88%.5%; :Is = 20°7)
s- PMMA
q of a s s o c i a t e d
(%)
q (in m o n o m e r u n i t s )
i
75
9
1,5
89
9
- II
2
55
8-9
2
35-40
10
.%0
io-ii
(I : 3.5%; H = 27.5%; S : 69%; :is = 6.0)
s-PMMA - I I I (I = 3.5%; H : 31.5%; S : 65%; :Is = 5.1)
1.5
aI,H,S - d e n o t e t h e f r a c t i o n of i s o t a c t i e , h e t e r o t a c t i c a n d s y n d i o t a c t i c r e s p e c t i v e l y ; Ts = {2S + H ) / H i s t h e m e a n s y n d i o t a c t i c l e n g t h .
triads,
b _ w i t h i-PMMA (I = 97%; H = 3%; S = 0).
assumed
that there
exists a certain
sequences
w h i c h is n e c e s s a r y
associated
segments
minimum length
of s t e r e o r e g u l a r
for stereocomplex formation and that the
are separated
by non-associated
sequences
of t h e
macromolecules. A syndiotactic sequence
sequence
isotactic step.
assuming first-order sequences
m w h i c h can follow a f t e r an i s o t a c t i c
(Bis(m)) or a f t e r a s y n d i o t a c t i c
the original syndiotactic
illustrated
of l e n g t h
step is repeated
Isotactic sequences
sequence
( B s s ( m ) ) is d e f i n e d
so that
are defined
similarly; the s y s t e m is
by the following example:
that the polymers can be described blarkov statistics, containing
m units
by Bernoulli statistics
or by
the w e i g h t f r a c t i o n ws(m) of s y n d i o t a c t i c is g i v e n b y t h e r e l a t i o n ( r e f . 103,121):
115
2 ws'm'~) = m P s - Pisl~ 1
m-I
" PsiPss
, m • 2
.
(3)
I n t h i s e q u a t i o n , P s i s t h e p r o b a b i l i t y of s y n d i o t a c t i c a d d i t i o n , P s s is t h e p r o b a b i l i t y o f s y n d i o t a c t i c p l a c e m e n t to a s y n d i o t a c t i c d i a d a n d t h e p r o b a b i l i t i e s Psi a n d Pis a r e d e f i n e d in a n a n a l o g o u s way.
The probabilities
obey the following relations:
A/2 Ps
= S + H/2;
Psi
= S + H/2
H/2
.
'
Pis
S
= I + H/2
;
T h e w e i g h t f r a c t i o n of all s y n d i o t a c t i c s e q u e n c e s
Pss
(4 )
- S + H/2
is g i v e n b y t h e
r e l a t i o n ( r e f . 103,121):
1 fs(1)
= Ps
' Pss
+Psi
(5)
" 1 - PisPsi
F r o m a c o m p a r i s o n of t h e f o u n d v a l u e s of p w i t h t h e d i s t r i b u t i o n o f s y n d i o t a c t i c s e q u e n c e l e n g t h s , ws(m) , t h e m i n i m u m l e n g t h q of a s s o c i a t e d s y n d i o t a c t i c s e q u e n c e s c a n b e c a l c u l a t e d b y m e a n s of t h e r e l a t i o n ( r e f . 103):
q-I J
(Ys~s)
P = fs(I)
- Z m=2
(6}
Ws(m )
w h e r e Y~ i s t h e f r a c t i o n o f s y n d i o t a c t i c u n i t s i n a s s o c i a t e d s e g m e n t s ( f o r t h e s t o i c h i o m e t r y i / s = 1/1.5, Y~ = 0.6; f o r t h e s t o i c h i o m e t r y i / s = 1/2, Y~ = 0.67}. Eq. 6 i s a p p l i c a b l e f o r Ys ~ Y~, while t h e v a l u e s o f (Y~/Ys)P f o r Y~ -- 0.6-0.67 do n o t d i f f e r a p p r e c i a b l y . The dependence
d of f s ( 1 ) - ~
ws(m} o n t h e s e q u e n c e l e n g t h d f o r s-PHMA
s t u d i e d b y u s is s h o w n i n Fig. 11.
T h e e x p e r i m e n t a l l y f o u n d v a l u e s (Yo'/Ys} p
are indicated by arrows and dashed horizontal lines; the corresponding intercepts
on t h e h o r i z o n t a l axis indicate the v a l u e ( q - l ) .
T h e v a l u e s of q o b t a i n e d b y m e a n s of Eq. 6 f o r t h e m i x t u r e s of i - a n d s-PMMA in C6D 6 a r e s h o w n i n T a b l e 2.
I n all c a s e s , t h e a g r e e m e n t is g o o d ,
i n d i c a t i n g t h a t i n b e n z e n e t h e m i n i m u m l e n g t h of s - s e q u e n c e s a s s o c i a t i o n , q = 8 to 10.
V a l u e s of q a r o u n d
o-dichlorobenzene and benzaldehyde.
necessary
for
10 u n i t s w e r e a l s o f o u n d f o r
F o r m i x t u r e s of i - a n d s - P P M A w i t h r =
2 i n CCI 4, CD3CN a n d i n DMF-d7, a s s o c i a t i o n o f p r a c t i c a l l y all m o n o m e r u n i t s (p ~ 95%) w a s o b s e r v e d
e v e n in t h o s e c a s e s w h e r e the s t e r e o r e g u l a r i t y
s - c o m p o n e n t w a s n o t v e r y h i g h ( s - P M M A - t y p e III i n T a b l e 2). that the minimum s-sequence
length necessary
of t h e
This indicates
for s t e r e o c o m p l e x formation in
116
I
l
l
l
|
l
l
l
l
l
1.0
0.8 %4,", t E "-~ 0.6
0.4
0.2,
I
I
I
4
I tl
tl
I
I
I
I
I
8 12 16 20 d (in monomer units)
d F i g . 11. D e p e n d e n c e o f t h e v a l u e f s ( 1 ) -m-~ w s ( m ) o n t h e s - s e q u e n c e length d f o r s - P M M A - 1 (S = 88.5%, H = 9%) (o); s - P M M A - 2 (S = 69%, H = 27.5%} (•); s - P M M A - 3 (S -- 66%, H = 31%) (o). T h e e x p e r i m e n t a l l y f o u n d v a l u e s (Y~/Ys)P f o r m i x t u r e s o f b e n z e n e s o l u t i o n s o f i-PMMA a n d s - P M M A a r e i n d i c a t e d b y a r r o w s a n d d a s h e d h o r i z o n t a l l i n e s (cf. Eq. 6) ( r e f . 103}. these
solvents
is of the order
q = 3; i n t o l u e n e ,
of q are valid at or below room temperature; temperatures
will b e d i s c u s s e d
The effect of the degree
determined
all t h e s e (proven
stereoregularity,
b y NMR s p e c t r a j
spectroscopy) s-sequences it j u s t i f i e s
the assumption
minimum length where
interaction
take part
prerequisite
i n T a b l e 3.
The finding
that
in aggregation.
that
s-PMbIA-3 does not take
the presence
of self-aggregation;
that only s-sequences
of s-sequences
fraction
of s-PMMA samples
osmometry~ light scattering
( r e f . 22~47,54,111) i n d i c a t e s is a necessary
of the associated
solutions
of conventional
viscometryj
was also
0.2 - 10% ( r e f . 110) a n d
for several
are summarized
media self-aggregation
values
at elevated
on association
The values
in the range
f r o m NMR m e a s u r e m e n t s
of various
the situation
of stereoregularity
of concentration
The quoted
in the following paragraph.
followed for s-PMMA self-aggregation. p, i n d e p e n d e n t
q ~ 4-5.
longer
Contrary
with practically
than
and
IR
of long also, in this case a certain
to the stereocomplex,
perfect
in place
stereoregular
117
TABLE 3 Quantitative
characterization
of ordered
Polymer
s-PMMA b y NMR a n d IR s p e c t r o s c o p y
F r a c t i o n of associated monomer units p f r o m NMR (%)
Solvent
Solution
F r a c t i o n of o r d e r e d s-PMMA f r o m IR a (%)
Solution
Solid State
s-PMMA-I
toluene
85
29
25
(S : 89.5%; H : 8.5%)
o-dichlorobenzene
73
27
29
butyl acetate
ca 90
b
24
s-PMMA-2
toluene
76
b
b
toluene c
0
0
0
(S = 85%; H = 12%) s-PMMA-3 (S = 66%; H = 31%)
adetermined from integrated intensities s t r e t c h i n g v i b r a t i o n s ; c f P a r t VI-A.
after
separation
of b a n d s
o f C=0
bnot measured Cno a s s o c i a t i o n w a s a l s o o b s e r v e d solutions
i-PMMA c h a i n s w a s c o n s i d e r e d , interactions structure
of s - sequences
in o-dichlorobe nz e ne
butyl acetate
i n t h e c a s e o f s-PMMA s e l f - a g g r e g a t i o n
must be considered.
is f o r m e d b y m u t u a l i n t e r a c t i o n
a r e of t h e minumum length
and
If we a s s u m e
of two s-sequences
mutual
that a stable ( b o t h of w h i c h
q or longer), then for the non-associated
f r a c t i o n , w e c a n w r i t e ( r e f . 111):*
1 - p - fi(1)
q-1 = 2 z ws(m ) m=2
Making u s e of the identity a shape
analogous
(7)
fi(1) + f s ( 1 ) = 1, Eq. 7 c a n b e t r a n s f o r m e d
into
to Eq. 6:
*All s - s e q u e n c e s c a n b e m e n t a l l y d i v i d e d i n t o t w o p a r t s ( m a r k e d a s w h i t e a n d black, respectively) with interaction always taking place between white and black sequences. Both parts have the same length distribution and the same m i n i m u m l e n g t h , q. T h e n i n c o n s e q u e n c e o f i m p e r f e c t s t e r e o r e g u l a r i t y , both c o m p o n e n t s p a r t i c i p a t e e q u a l l y in the n o n - a s s o c i a t e d f r a c t i o n of s - s e q u e n c e s , 1 - p - fi(1).
118
q-1 p = fs(1) - 2 ~ Ws(m). m=2
(8)
d For the studied polymers, the plots of fs(1) - 2mz=2 ws(m) against the length of s-sequences d are s h o w n in Fig. 12.
T h e experimentally determined values
of the associated fraction p are indicated b y arrows and horizontal dashed lines in these plots.
The corresponding intercepts on the horizontal axis
indicate the value (q -1), w h e r e q is the sequences
(cf. Eq. 8).
m i n i m u m length of associated
Fig. 12 exhibits good agreement, indicating that the
m i n i m u m length of aggregated s-sequences for s - P M M A
self-aggregation in
toluene (and similarly in o-dichlorobenzene a n d BAC) is equal to 9 m o n o m e r units (ref. 54,111).
.~ 1"0I N~ ,
0.8
0.6
0.40,2O15 20 d (in monomer units}
10
d
Fig. 12. D e p e n d e n c e of the value fs(1) - ~=_z2 ws(m) on the s-sequence length d for s - P M M A - I (S -- 89.5%; H = 8.5%) (o);-s-PMMA-2 (S -- 85%; H = 12%)) (e); s - P M M A - 3 (S = 66%; H -- 31%) (A). T h e experimentally found values of associated fraction p for toluene-d 8 solutions of s - P M M A are indicated b y arrows a n d dashed horizontal lines (ref. 111).
ll9 C o n t r a r y to t h e m e n t i o n e d s o l v e n t s , in CC14 (which is a v e r y p o o r s o l v e n t f o r PMMA), a p p r e c i a b l e s e l f - a g g r e g a t i o n t a k e s p l a c e e v e n w i t h s-PMI~IA of low stereoregularity
{s-PMMA-3), a s i n d i c a t e d b y t h e r e s u l t s of NFIR, o s m o m e t r y
and cloud-point curves
( r e f . 3,53,55).
C. T h e r m a l s t a b i l i t y a n d d e c o m p o s i t i o n of a ~ g r e ~ a t e s The d e c o m p o s i t i o n of s t e r e o c o m p l e x a g g r e g a t e s in a c e r t a i n t e m p e r a t u r e r a n g e ( t h e i r " m e l t i n g " ) h a s b e e n p r o v e d b y v a r i o u s m e t h o d s a n d d e s c r i b e d in a n u m b e r of p a p e r s (ref. 1,33,40,42,56,60,64-66,69,74,75,82,83,98,103-105).
In
t h e c i t e d p a p e r s , v a r i o u s t e m p e r a t u r e r a n g e s c o r r e s p o n d i n g to t h e " m e l t i n g " of s t e r e o c o m p l e x a g g r e g a t e s a r e q u o t e d , d u e to t h e c i r c u m s t a n c e t h a t t h e s t a b i l i t y of t h e s t e r e o c o m p l e x s t r o n g l y d e p e n d s on t h e s t e r e o r e g u l a r i t y of t h e i n t e r a c t i n g p o l y m e r s a n d also on s o l v e n t . A l r e a d y in t h e f i r s t p a p e r s on t h e s t e r e o c o m p l e x , it was o b s e r v e d t h a t t h e m e l t i n g p o i n t of t h e gel d e c r e a s e s w i t h t h e d e c r e a s i n g t a c t i c i t y of t h e s - c o m p o n e n t , s i m i l a r l y a s t h e t e m p e r a t u r e s of a g g r e g a t e d e c o m p o s i t i o n d e t e r m i n e d f r o m t u r b i d i m e t r i c m e a s u r e m e n t s ( r e f . 1,33,82,83).
The c h a r a c t e r
of t h e t h e r m a l s t a b i l i t y of s t e r e o c o m p l e x a g g r e g a t e s in d e p e n d e n c e on t h e s t e r e o r e g u l a r i t y of t h e s - c o m p o n e n t was s t u d i e d in g r e a t e r d e t a i l b y NMR s p e c t r o s c o p y ( r e f . 103).
The t e m p e r a t u r e d e p e n d e n c e of t h e a s s o c i a t e d
f r a c t i o n p f o r m i x t u r e s o f i - a n d s-PMMA in b e n z e n e , w i t h v a r i o u s s t e r e o r e g u l a r i t y of t h e s - c o m p o n e n t , is i l l u s t r a t e d in Fig. 13.
At a g i v e n
t e m p e r a t u r e , " m e l t i n g " p r o c e e d s v e r y q u i c k l y u p to a c e r t a i n v a l u e of p which does not f u r t h e r
c h a n g e w i t h time.
From Fig. 13, it c a n b e s e e n t h a t
f o r all s a m p l e s , m e l t i n g b e g i n s a t a p p r o x i m a t e l y t h e same t e m p e r a t u r e (['40"C).
F o r m i x t u r e s w i t h s-PMMA of h i g h e r s t e r e o r e g u l a r i t y , t h e " m e l t i n g "
r a n g e b r o a d e n s and complete dissociation takes place at h i g h e r temperatures.
At t h e same time, t h e s h a p e of t h e t e m p e r a t u r e d e p e n d e n c e
d o e s n o t d e p e n d o n t h e mixing ratio.
A c o m p a r i s o n of t h e t e m p e r a t u r e
d e p e n d e n c e s of p f r o m Fig. 13 w i t h t h e c o r r e s p o n d i n g d e p e n d e n c e s of t h e d q u a n t i t y fs(1) -mZ=2 Ws(m) o n s e q u e n c e l e n g t h d (Fig. I I ) r e v e a l s t h a t t h e y a r e v e r y similar. aggregates
This i n d i c a t e s t h a t t h e d e c o m p o s i t i o n of s t e r e o e o m p l e x
b y h e a t i n g c o r r e s p o n d s to t h e d i s t r i b u t i o n of s e q u e n c e l e n g t h s o f
t h e s - c o m p o n e n t ( t h e i - c o m p o n e n t is almost p e r f e c t ) , while t h e minimum s e q u e n c e l e n g t h n e c e s s a r y f o r a s s o c i a t i o n (q) e x h i b t s a n a l m o s t l i n e a r t e m p e r a t u r e d e p e n d e n c e in a c e r t a i n t e m p e r a t u r e r a n g e .
With some
a p p r o x i m a t i o n , it c a n t h e r e f o r e be s t a t e d t h a t a d e f i n e d " m e l t i n g " t e m p e r a t u r e c o r r e s p o n d s to a c e r t a i n l e n g t h of a s s o c i a t e d s e q u e n c e s .
With m i x t u r e s of i -
a n d s-PMMA in b e n z e n e , t h e l e n g t h e n i n g of t h e s - s e q u e n c e b y o n e monomer u n i t i n c r e a s e s t h e m e l t i n g t e m p e r a t u r e b y ~2"C.
An a p p r e c i a b l e d e v i a t i o n
from a l i n e a r t e m p e r a t u r e d e p e n d e n c e o f t h e minimum l e n g t h q c a n
120
8O
60
40-
20
0
I
I
I
30 F i g 13. T e m p e r a t u r e for various mixtures i-PMMA + s - P M M A - 1 (l:l); ~ , i-PMMA + s - P M M A - 3 (S -- 66%; be observed
I
I
I
70 90 ternperGture, "C
dependence of the fraction p of associated monomer units o f i-PMMA (I -- 97%; H -- 3%) a n d s - P M M A i n b e n z e n e ; o, (S = 88.5%; H = 9%) (1:2); (o), i-PMMA + s - P M M A - I s - P M M A - 2 (S = 69%; H = 27.4%) (1:2); a, i-PMMA + H = 31%) (1:1.5) ( r e f . 103).
at temperatures
decomposition dependence
l
50
(cf. F i g s . l l
of fs(1) - z
approaching and
the temperature
13); t h i s i s q u i t e
ws(m) on the length
of complete
understandable
d approaches
because
the
zero
asymptotically. The character
of the temperature
( r e f . 103) i s s i m i l a r to t h a t and
observed
s-PMMA, the temperature
the used
solvent.
of stereocomplex high upper
range
The upper aggregates
stereoregularity
For a given
of stereocomplex
generated
"melting"
by interaction
lies at temperaturaes
i-PMMA a n d
f r o m NMR s p e c t r a )
of p in other
in benzene.
limit of the temperature
limits of the temperature
stereoregular
dependences
range
around
of "melting"
range
solvents
are
given
of i-
depends
on
of decomposition
of i- and
s-PMMA of
1 2 0 - 1 3 0 " C ( F i g . 8). for mixtures
s-PMMA of lower stereoregularity
for various
solvents mixture
The
of highly
(as determined
in Table 4 in Part
V-E.
It
can be seen that stereocomplex aggregates are most stable in CC14 a n d in toluene; the high thermal stability of the stereocomplex in toluene w a s also revealed b y m e a s u r e m e n t s of gel melting points (ref. 67,74). The finding that associated segments containing long s-sequences "melt" at higher temperatures than segments formed b y short s-sequences and a certain similarity of the described association with crystallization imply that the binding Gibbs e n e r g y (per tool of m o n o m e r
units) will be higher for
121 TABLE 4 Values of the fraction sequences
of associated
units,
of the minimum length
q (both at 25°C) and of the temperature
of stereocomplex of solubility
aggregates
parameters
3%; S : 0} a n d
Tm in different
5; v a l u e s
of complete
solvents
of p for mixtures
of dipole moments p and o f i-PMMA (I : 97%; H =
s - P M M A (I : 3%; H : 31%; S : 66%), w e i g h t
( d a t a f r o m r e f . 103 a n d
Solvent
unpublished
p
ratio i/s
p
(cal cm-3) I/2
q
T m
(%)
('C)
CC14
0
8.6
95
3
95 a
acetonitrile
3.4
11.9
95
3
70
DMF
3.8
12.1
90
3
_b
toluene
0.37
8.9
80
4-5
85
o-dichlorobenzene
2.5
10.0
38
9-10
70
benzene
0
9.2
35-40
8-10
60
benzaldehyde
2.8
9.4
25
12-13
60
chloroform
1.05
9.3
0
-
-
aEstimated to 75"C
from the course
= 1/2
data).
6
(debye)
of associated decomposition
of the temperature
dependence
of p measured
up
bNot measured
associated
segments
stereoregularity predominate heats
formed
by long s-sequences
of the i-component
in s-PMMA of high
is assumed)
stereocomplex
formation
depends
for higher
( r e f . 103).
stereoregularity.
o f m i x i n g , B i r o ~ e t al. h a v e a c t u a l l y
strongly
(a p r a c t i c a l l y
Long sequences
From measurements
proved
i n DMF c o r r e s p o n d i n g
on the stereoregularity
perfect
( r e f . 93) t h a t
to t h e s t o i c h i o m e t r i c
of the s-component
of the
the heat of
and
ratio
(i/s)
is higher
stereoregularity.
The temperature
dependence
of the fraction
p of associated
units
characterizing the thermal stability of i- and s - P M M A self-aggregates in o-dichlorobenzene (ref. 2,3,102) is demonstrated in Fig. 14.
The dependences
of the fraction p in toluene had a perfectly similar character and their concentration independence in the range 0.2-10% was likewise observed (ref. 54,109,110). Fig. 14 demonstrates the completely different thermal stability of the i- and
s-PMMA self-aggregates.
self-aggregates very results
stable
and
While the fraction
at room temperature they
of osmometry,
decompose viscometry,
is very
completely
p of s-PMMA
high, these
aggregates
at 60"C, in agreement
light scattering
and
are not with the
IR s p e c t r o s c o p y
(ref.
122
80 d.
60 s-PMMA 40
-
20 i-PMMA i~,
0
50
I
100
I
\ \
150 200 temperQture,°C
Fig. 14. T e m p e r a t u r e d e p e n d e n c e of t h e f r a c t i o n of a s s o c i a t e d monomer u n i t s p f o r s o l u t i o n s of i-PMMA ( ) a n d s-PMMA ( - - - ) in o - d i c h l o r o b e n z e n e ( r e f . 3,102).
47,54,102).
The amount of i-PMMA s e l f - a g g r e g a t e s at room temperature is
relatively small, but these a g g r e g a t e s exhibit a high thermal stability; temperatures above 160°C, comparable with the melting temperature of solid i-PMMA, are n e c e s s a r y for their complete decomposition. While for solutions of i-PMMA in toluene-d8 only a small content of a g g r e g a t e s (p = 10%) was observed even at -60"C and this content did not change in the r a n g e -60 to 110"C (ref. 119), for solutions of i-PMMA in BAC a
s h a r p i n c r e a s e of t h e a g g r e g a t e d f r a c t i o n p t a k e s p l a c e a t t e m p e r a t u r e s below 0"C, w i t h m a c r o s c o p i c s e p a r a t i o n of most of i-PMMA f r o m t h e s o l u t i o n ( r e f . 47).
Also, most of t h e s-PMMA is a g g r e g a t e d
c a s e , h o w e v e r , a t t e m p e r a t u r e s below 60"C.
( s e p a r a t e d ) in BAC; in t h i s
It is i n t e r e s t i n g t h a t b o t h i - a n d
s-PMMA s e p a r a t e from BAC s o l u t i o n a t t e m p e r a t u r e s a b o v e t h e o t e m p e r a t u r e of at-PMMA (-20"C). A c o m p a r i s o n of F i g s . 8,13 a n d 14 i n d i c a t e s t h a t t h e t h e r m a l s t a b i l i t y of s t e r e o c o m p l e x a g g r e g a t e s f o r m e d b y i n t e r a c t i o n of i - a n d s-PMMA of h i g h s t e r e o r e g u l a r i t y is c o n s i d e r a b l y h i g h e r t h a n t h e t h e r m a l s t a b i l i t y of t h e s e l f - a g g r e g a t e s of h i g h l y s t e r e o r e g u l a r s-PMMA.
Together with the finding
t h a t b y c o o l i n g of a m i x t u r e of t o l u e n e s o l u t i o n s of i - a n d s-PMMA f r o m 130" to 25"C no s e l f - a g g r e g a t e s a r e f o r m e d , b u t t h e s t e r e o c o m p l e x is g e n e r a t e d , t h i s i n d i c a t e s t h a t t h e i n t e r a c t i o n s of t h e s t e r e o c o m p l e x t y p e a r e s t r o n g e r t h a n t h e i n t e r a c t i o n s l e a d i n g to s-PMMA s e l f - a g g r e g a t i o n ( r e f . 22).
123 D. K i n e t i c s of a g g r e g a t i o n a n d e f f e c t of t h e r m a l h i s t o r y The time c o u r s e of PMMA s t e r e o c o m p l e x f o r m a t i o n w a s followed b y v a r i o u s m e t h o d s b o t h f o r d i l u t e s o l u t i o n s a n d f o r g e l s of c o n c e n t r a t e d s o l u t i o n s . V i s c o m e t r i c m e a s u r e m e n t s h a v e s h o w n t h a t t h e c h a n g e s of v i s c o s i t y w i t h time (i.e., i t s d e c r e a s e o r g r o w t h , in d e p e n d e n c e on s o l v e n t - - s e e P a r t IV-A, V i s c o m e t r y ) is t h e s h a r p e r , t h e h i g h e r t h e c o n c e n t r a t i o n of t h e s o l u t i o n (ref. 44,67).
M e a s u r e m e n t s of l i g h t s c a t t e r i n g h a v e y i e l d e d t h e time d e p e n d e n c e s
of /~/wapp a n d of t h e g y r a t i o n r a d i u s Rg f o r s t e r e o c o m p l e x a g g r e g a t e s in DMF ( r e f . 43).
While Flwapp i n c r e a s e s s h a r p l y a l r e a d y d u r i n g t h e f i r s t m i n u t e s ,
Rg r e m a i n s c o n s t a n t f o r a r e l a t i v e l y l o n g time a n d i t s i n c r e a s e is o b s e r v e d o n l y a f t e r a v e r y l o n g time (~ d a y ) .
A similar c h a r a c t e r of t h e time
d e p e n d e n c e s of Mwp p a n d Rg was also o b s e r v e d b y B e l n i k e v i t c h e t al. ( r e f . 44), who h a v e a l s o o b s e r v e d t h a t t h e s t e r e o c o m p l e x is f o r m e d more q u i c k l y in DMF t h a n in d i o x a n e .
The o b s e r v a t i o n t h a t t h e size of t h e s t e r e o e o m p l e x
a g g r e g a t e s d o e s n o t c h a n g e f o r a r e l a t i v e l y l o n g time while t h e i r m a s s i n c r e a s e s i n d i c a t e s a g r o w t h of t h e d e n s i t y of a g g r e g a t e d monomer u n i t s (i.e., the aggregates
g r o w more c o m p a c t w i t h time).
The i n c r e a s e of Rg a f t e r a
l o n g time is e x p l a i n e d b y t h e p r o c e s s of s e c o n d a r y a g g r e g a t i o n of s t e r e o c o m p l e x p a r t i c l e s a n d f o r m a t i o n of l a r g e r s t r u c t u r e s .
Such a secondary
p r o c e s s is a l s o i n d i c a t e d b y t h e r e s u l t s of v i s c o m e t r i c a n d DSC m e a s u r e m e n t s ( r e f . 51,74,96). NMR m e a s u r e m e n t s h a v e s h o w n t h a t w i t h m i x t u r e s of i - a n d s-PMMA in CD3CN o r CC14 ( c o n c e n t r a t i o n 10%) a t room t e m p e r a t u r e t h e p r o c e s s of s t e r e o c o m p l e x f o r m a t i o n is so r a p i d t h a t it c a n n o t be followed b y t h i s technique.
I n b e n z e n e , o - d i c h l o r o b e n z e n e a n d b e n z a l d e h y d e , a s s o c i a t i o n is
r a p i d o n l y a t t h e b e g i n n i n g , w h e n a v e r y q u i c k e s t a b l i s h m e n t of a c e r t a i n v a l u e of t h e a g g r e g a t e d f r a c t i o n p is o b s e r v e d ; f u r t h e r a s s o c i a t i o n is a v e r y slow p r o c e s s a n d t h e e q u i l i b r i u m s t a t e is r e a c h e d a f t e r a v e r y l o n g time ( r e f . 103).
At t h e same time, t h e r e l a t i v e n u m b e r of u n i t s t a k i n g p a r t in t h i s slow
p r o c e s s i n c r e a s e s with the d e c r e a s i n g s t e r e o r e g u l a r i t y of the s - c o m p o n e n t . T h i s i n d i c a t e s v e r y r a p i d a s s o c i a t i o n o f l o n g s - s e q u e n c e s a n d slow a s s o c i a t i o n of s h o r t s - s e q u e n c e s c o n n e c t e d p r o b a b l y w i t h some r e a r r a n g e m e n t of t h e already generated structure.
P y r l i k a n d R e h a g e ( r e f . 88,91) h a v e m e a s u r e d
t h e time d e p e n d e n c e s of t h e c o m p o n e n t s o f t h e s h e a r m o d u l u s f o r s t e r e o c o m p l e x g e l s in o - x y l e n e .
T h e y o b s e r v e d t h a t t h e e q u i l i b r i u m v a l u e s of
G' i n c r e a s e w i t h d e c r e a s i n g t e m p e r a t u r e ; t h i s t h e y e x p l a i n b y p r o c e e d i n g c r y s t a l l i z a t i o n w i t h d e c r e a s i n g t e m p e r a t u r e a n d t h u s a g r o w i n g d e g r e e of crosslinking (the crystallites act as crosslink points).
The r e a s o n f o r
p r o c e e d i n g c r y s t a l l i z a t i o n a t d e c r e a s i n g t e m p e r a t u r e is s e e n in t h e t e m p e r a t u r e d e p e n d e n c e of t h e minimum l e n g t h of s t e r e o r e g u l a r s - s e q u e n c e s n e c s s a r y f o r c r y s t a l l i z a t i o n , in a g r e e m e n t w i t h t h e r e s u l t s o f NMR
124 spectroscopy
(see p r e c e d i n g
paragraph).
T h e k i n e t i c s of s e l f - a g g r e g a t i o n
of s-PMMA i n t o l u e n e a n d BAC w a s
followed b y a c o m b i n a t i o n of NMR s p e c t r o s c o p y , light scattering
and turbidimetry
r a t e of s-PMMA s e l f - a g g r e g a t i o n
IR s p e c t r o s c o p y ,
( r e f . 38,47,54,111).
viscometry,
It w a s p r o v e d t h a t t h e
increases with decreasing temperature
and
with increasing concentration, with the solvent playing an important part.
At
t h e s a m e time, v a r i o u s m e t h o d s e x h i b i t v a r i o u s s e n s i t i v i t y to d i f f e r e n t p h a s e s of t h e a g g r e g a t i o n t h e time d e p e n d e n c e
process.
T h e s i t u a t i o n is i l l u s t r a t e d in Fig. 15, e x h i b i t i n g
of t h e f r a c t i o n of a g g r e g a t e d
NMR s p e c t r a a n d t h e time d e p e n d e n c e i d e n t i c a l s a m p l e of s-PMMA s o l u t i o n i n
units p determined from
of t h e t u r b i d i t y BAC.
t h a t while the f r a c t i o n p i n c r e a s e s from t h e v e r y turbidity
b e g i n n i n g , a g r o w t h of
o n l y t a k e s p l a c e a t a time w h e n t h e f r a c t i o n p a l m o s t d o e s n o t
c h a n g e a n y more.
Similarly as with the stereocomplex a g g r e g a t e s ,
p r i m a r y a n d a s e c o n d a r y p r o c e s s c a n be a s s u m e d . process
~- m e a s u r e d w i t h a n
Fig. 15 c l e a r l y d e m o n s t r a t e s
also here a
During the primary
( b e s i d e s NMR s p e c t r o s c o p y , t h i s i s a l s o d e t e c t e d b y IR s p e c t r o s c o p y ) ,
"intramolecular" ordering s-sequences
t a k e s p l a c e i n c o n s e q u e n c e of i n t e r a c t i o n s of
(the term "intramolecular" here also includes, for example,
d o u b l e - c h a i n i n t e r a c t i o n s ) a n d c r y s t a l l i t e - l i k e domains are formed (the so c a l l e d " g l o b u l a t i o n " s t a g e a c c o r d i n g to r e f . 38). certain temperature decreasing
At t h e s a m e time, in a
r a n g e , t h e e q u i l i b r i u m v a l u e s of p i n c r e a s e w i t h
temperature
of a g g r e g a t i o n
(Fig. 10); s i m i l a r l y a s in t h e c a s e of
the stereoeomplex, t h i s can be explained b y the d e c r e a s i n g s-sequences
necessary
for the interaction energy
e n e r g y of m o l e c u l a r m o t i o n a t d e c r e a s i n g t e m p e r a t u r e . the "globules" further
aggregate
m i n i m u m l e n g t h of
to e x c e e d t h e t h e r m a l With p r o c e e d i n g time,
(secondary process) under
f o r m a t i o n of
l a r g e r p a r t i c l e s , c a u s i n g , f o r e x a m p l e , t h e s h a r p i n c r e a s e of t u r b i d i t y (flocculation stage).
I
I
50
100
--IT
p
/ "t, min
150
Fig. 15. Correlation of (I) p - t and (2) ~-t c u r v e s for s-PMMA (S = 91.5%; H "7.5%) in BAC (cone. 9x10-3g cm-3) at 48"C; p is the fraction of immobilized monomer u n i t s determined by NMR, ~- is the t u r b i d i t y and t is the aggregation time (rain); p an ~" are expressed in a r b i t r a r y u n i t s (ref. 38).
125 T h e circumstance that for the stereocomplex aggregates in some solvents a v e r y long time is needed for the attainment of the equilibrium state leads to a different course of various quantities during heating and cooling. hysteresis curves for the P M M A
Such
stereocomplex have been observed in
viscosity (ref. 64), dielectric (ref. 52), dynamicomechanical
(ref. 91} a n d N M R
spectroscopic mesurements; the latter have also s h o w n that the stereocomplex in a solution which has not reached the equilibrium state at repeated heating e x h i b i t s a d i f f e r e n t b e h a v i o r ( t h e r a n g e of " m e l t i n g " c o r r e s p o n d i n g segments with short s-sequences spectroscopy,
it w a s f u r t h e r
i s m i s s i n g } ( r e f . 103}.
to
By NMR
s h o w n t h a t t h e a t t a i n m e n t of e q u i l i b r i u m v a l u e s
of p w h i c h f o r m i x t u r e s of i - a n d s-PMMA in b e n z e n e t a k e s a v e r y l o n g time at room t e m p e r a t u r e if a g g r e g a t i o n
( w e e k s to m o n t h s } c a n b e r e c h e d a l m o s t i n s t a n t a n e o u s l y
takes place at -70"C or even lower temperatures.
This is
p r o b a b l y a c o n s e q u e n c e of t h e c i r c u m s t a n c e t h a t t h e r a t e of a g g r e g a t i o n increases with decreasing aggregation
temperature
s o t h a t a t low t e m p e r a t u r e s
is p r o b a b l y e v e n m o r e r a p i d t h a n t h e p r o c e s s of s o l v e n t
solidification.
T h e time e f f e c t a l s o h a s to b e c o n s i d e r e d i n c o m p a r i s o n s of
v a r i o u s s t u d i e s of s-PMMA s e l f - a g g r e g a t i o n
{ref. 38,47,54}.
H o w e v e r , b o t h w i t h t h e s t e r e o c o m p l e x a n d w i t h s-PMMA s e l f - a g g r e g a t e s , e f f e c t s of t h e r m a l h i s t o r y h a v e b e e n o b s e r v e d than the above described
which have a different origin
k i n e t i c s of a g g r e g a t i o n .
In d y n a m i c a l - m e c h a n i c a l
m e a s u r e m e n t s , P y r l i k e t al. ( r e f . 88,89) h a v e o b s e r v e d
t h a t if t h e m i x t u r e of
i - a n d s-PMMA i n o - x y l e n e w a s h e a t e d to 120"C (i.e., o n l y a b o u t 10"C a b o v e t h e m e l t i n g p o i n t of t h e gel}, t h e n a f t e r c o o l i n g to 80"C g e l f o r m a t i o n p r o c e e d s m u c h m o r e r a p i d l y t h a n a f t e r p r e v i o u s h e a t i n g to 145"C.
From
t u r b i d i m e t r i c m e a s u r e m e n t s , a s i m i l a r e f f e c t of t h e r m a l h i s t o r y w a s o b s e r v e d also for aggregation
in d i l u t e s o l u t i o n s of s-PMMA in BAC ( r e f . 38}.
In both
c a s e s , t h i s b e h a v i o r is e x p l a i n e d b y t h e e x i s t e n c e o f s t a b l e n u c l e i w h i c h a r e a b l e to s u r v i v e f o r s o m e time a t t e m p e r a t u r e s "melting".
even above the upper
limit of
N u c l e a t i o n m e c h a n i s m s a r e a l s o u s e d to e x p l a i n t h e o b s e r v a t i o n
that the mechanical properties temperatures
of s t e r e o c o m p l e x g e l s g e n e r a t e d
differ considerably at a given temperature
c o m p a r i s o n of the r e s u l t s o b t a i n e d by light s c a t t e r i n g o s m o m e t r y , v i s c o m e t r y a n d NMR s p e c t r o s c o p y
at various
( r e f . 88,89).
A
w i t h t h e r e s u l t s of
i n d i c a t e s t h a t the f r a c t i o n of
s u c h n u c l e i i n s o l u t i o n s of s-PMMA in BAC m u s t be v e r y small {ref. 38}. this system, another spectroscopy
distinct "hysteretie"
when aggregates
( p r e c i p i t a t e } f o r m e d a t 25"C w e r e h e a t e d .
16 s h o w s t h a t t h e g i v e n " e q u i l i b r i u m " v a l u e of p r e a c h e d d u r i n g at a higher temperature
In
e f f e c t w a s f o u n d b y NMR
than the aggregation
temperature
Fig.
h e a t i n g lies
needed for
r e a c h i n g t h e s a m e " e q u i l i b r i u m " v a l u e of p ( d u r i n g t h e a g g r e g a t i o n process}.
This i n d i c a t e s t h a t some s t r u c t u r a l
rearrangements
s e e m to o c c u r
126
100 --', 80
""
~,
60 40!
2bl I1Q
20
40 60 80 ternperat ure,'C
Fig. 16. D e p e n d e n c e of t h e " e q u i l i b r i u m " v a l u e s of f r a c t i o n p ( a g g r e g a t e d m o n o m e r u n i t s ) o n t e m p e r a t u r e of s-PMMA iS = 91.5%; H - 7.5%; c o n c . 9.0 x 1 0 - 3 g c m -3) i n BAC ( l a ) a n d t o l u e n e - d 8 (2a), c o m p a r e d w i t h t h e t e m p e r a t u r e d e p e n d e n c e of f r a c t i o n p d u r i n g t h e h e a t i n g of a g g r e g a t e s f o r m e d a t 25"C ( c u r v e s l b a n d 2b) ( r e f . 38).
a l s o in t h e p r e c i p i t a t e ; t h e s y s t e m t e n d s to h i g h e r s t a b i l i t y a l s o d u r i n g a g e i n g of t h e p r e c i p i t a t e .
E. E f f e c t of s o l v e n t o n t h e f o r m a t i o n of a g g r e g a t e s The original papers
d e s c r i b e s t e r e o c o m p l e x formation only in polar
s o l v e n t s like DMF o r a c e t o n i t r i l e ( r e f . 1,33} b u t Liu a n d Liu {ref. 65} w e r e t h e f i r s t to o b s e r v e benzene or toluene.
s t e r e o c o m p l e x f o r m a t i o n a l s o i n n o n p o l a r s o l v e n t s like Solid s t e r e o c o m p l e x s a m p l e s i s o l a t e d f r o m a c e t o n e ,
acetonitrile or benzene solution exhibit the same X-ray pattern
( r e f . 69).
T h e e f f e c t o f s o l v e n t o n s t e r e o c o m p l e x f o r m a t i o n c a n be c o m p a r e d q u a n t i t a t i v e l y f r o m t h e r e s u l t s of NMR s p e c t r o s c o p y characterizing i n T a b l e 4.
( r e f . 103).
Data
s t e r e o c o m p l e x f o r m a t i o n i n a s e r i e s of s o l v e n t s a r e s u m m a r i z e d
V a l u e s of p f o r m i x t u r e s w i t h t h e s - c o m p o n e n t of l o w e r
stereoregularity
are cited intentionally.
high stereoregularity,
t h e v a l u e s of p a r e m u c h l e s s s e n s i t i v e to t h e n a t u r e
of t h e s o l v e n t (p = 85 - 100%}. corresponding
F o r m i x t u r e s of i - w i t h s-PMMA of
T h e s a m e i s t r u e of t h e t e m p e r a t u r e
values
to c o m p l e t e d e c o m p o s i t i o n , Tin, w h i c h o f t e n lie a b o v e t h e
b o i l i n g p o i n t o f t h e s o l v e n t w i t h s - c o m p o n e n t s of v e r y h i g h s t e r e o r e g u l a r i t y . F r o m T a b l e 4, it i s e v i d e n t t h a t t h e e x t e n t of s t e r e o c o m p l e x f o r m a t i o n i s n o t d e t e r m i n e d b y t h e p o l a r i t y of t h e s o l v e n t .
P r a c t i c a l l y all m o n o m e r i c u n i t s
a r e a s s o c i a t e d b o t h i n t h e h i g h l y p o l a r a e e t o n i t r i l e o r DMF a n d in n o n p o l a r CCI4.
Lower p values are observed
benzaldehyde)
in b o t h polar ( o - d i c h l o r o b e n z e n e ,
and nonpolar (benzene} aromatic solvents.
Neither can the
medium e f f e c t s u p o n s t e r e o c o m p l e x formation be c o r r e l a t e d with the solubility parameter
~ ( s q u a r e r o o t of t h e c o h e s i o n e n e r g y
association has been observed
density} alone.
No
i n c h l o r o f o r m , e v e n f o r m i x t u r e of i-PMMA w i t h
127 s-PMMA of h i g h s t e r e o r e g u l a r i t y
a t low t e m p e r a t u r e
(-50"C).
S o l v e n t s in
w h i c h s t e r e c o m p l e x f o r m a t i o n t a k e s p l a c e c a n b e c l a s s i f i e d a c c o r d i n g to t h e m i n i m u m l e n g t h of a s s o c i a t e d s - s e q u e n c e s ,
q.
In agreement with the
t e r m i n o l o g y i n t r o d u c e d o r i g i n a l l y b y C h a l l a e t al. (ref. 35), t h e s o l v e n t s w i t h q ~ 3 m a y be r e g a r d e d
a s s t r o n g l y c o m p l e x i n g , t h e s o l v e n t s w i t h q ~ 10 a s
weakly complexing and chloroform as non-complexing.
T h i s c l a s s i f i c a t i o n is
a l s o in a g r e e m e n t w i t h t h e c l a s s i f i c a t i o n g i v e n in r e f . 37, a n d it is s u m m a r i z e d i n T a b l e 5~ w h e r e s o m e f u r t h e r
solvents are also included.
Some
d i s c r e p a n c i e s exist c o n c e r n i n g the clas s ificatio n of toluene; c o n s i d e r i n g the v a l u e s of t h e m i n i m u m l e n g t h q, t h i s s o l v e n t is c l a s s i f i e d a s s t r o n g l y c o m p l e x i n g a n d t h i s is s u p p o r t e d
b y t h e r e l a t i v e l y h i g h t h e r m a l s t a b i l i t y of
t h e s t e r e o c o m p l e x i n t h i s s o l v e n t {Table 4 a n d r e f . 67,74).
On t h e o t h e r
h a n d , t h e v i s c o m e t r i c b e h a v i o r (ref. 35) a n d e s p e c i a l l y t h e c a l o r i m e t r i c a l l y d e t e r m i n e d v a l u e s of t h e h e a t of f o r m a t i o n of t h e s t e r e o c o m p l e x ( r e f . 93) classify toluene as weakly complexing.
The tendency
to s t e r e o c o m p l e x
f o r m a t i o n is v e r y w e a k i n c h l o r o b e n z e n e (ref. 44,65,77).
T h e s t e r e o c o m p l e x is
a l s o f o r m e d in s o m e o t h e r s o l v e n t s like o - x y l e n e ( r e f . 67,88), t r i m e t h y l b e n z e n e ( r e f . 67), m e t h y l a c e t a t e r e f . 58), e t h y l a c e t a t e a n d BAC ( r e f . 45,71).
TABLE 5 C l a s s i f i c a t i o n of s o l v e n t s a c c o r d i n g to t h e i r t e n d e n c y to s t i m u l a t e PMMA s t e r e o c o m p l e x f o r m a t i o n ( r e f . 35,37,103) Strongly complexing
Weakly complexing Non-complexing
CC14
DMSO
benzene
chloroform
acetonitrile
methyl isobutyrate
o-dichlorobenzene
dichloromethane
DMF
THF
benzaldehyde
acetone
MMA
dioxane thiophene ? ~- t o l u e n e -~ ?
T h e v a l u e s of t h e a g g r e g a t e d
? ~- c h l o r o b e n z e n e -~ ?
f r a c t i o n p, c h a r a c t e r i z i n g
self-aggregation
i-PMMA a n d s-PMIVIA i n v a r i o u s s o l v e n t s , a r e s u m m a r i z e d in T a b l e 6.
of
From
t h i s t a b l e , it c a n be s e e n t h a t t h e v a l u e s of p f o r i-PMMA a r e n o t v e r y h i g h a n d t h a t t h e y show little d e p e n d e n c e on s o l v e n t ( p e r h a p s with t h e exception of chloroform).
S e l f - a g g r e g a t i o n o f s-PMMA w a s m o s t l y o b s e r v e d
p o l y m e r of h i g h s t e r e o r e g u l a r i t y .
only for the
An e x c e p t i o n i s CC14, w h e r e a g g r e g a t i o n
e v e n of c o n v e n t i o n a l PMMA i s a p p r e c i a b l e .
H o w e v e r , f r o m a c o m p a r i s o n of
T a b l e s 5 a n d 6, it c a n be s e e n t h a t t h e e f f e c t of s o l v e n t o n s t e r e o c o m p l e x
128 TABLE 6 V a l u e s of t h e f r a c t i o n of a s s o c i a t e d u n i t s p (at 25"C) f o r i-PMMA a n d s-PMMA of v a r i o u s s t e r e o r e g u l a r i t y
in v a r i o u s s o l v e n t s {data f r o m r e f .
2,3,38,47,54,102,109,110)
Solvent
i-PMMA
s-PMMA-1
s-PMMA-2
(I:97% H:3% S : 0 ) (I:2.5% H:9% S:88.5%) (I:3.5% H:31.5% S:65%)
CC14
20-24
-~100a
40-48
toluene
10
85
0
o-dichlorobenzene
15
70-85
0
butylacetate
_b
90
0
DMF
17
18
0
acetonitrile
18-23
0-5
_b
benzene
12-15
5
0-4
chloroform
0-12
0
0
as-PMMA-1 could not be dissolved in CCI4 bnot measured
formation and on self-aggregation of s-PMMA is not parallel and this is most evident for acetonitrile.
Using a terminology analogous to that used for the
stereocomplex, then CCI4, butyl acetate, toluene, o-dichlorobenzene can be classified as strongly promoting self-aggregation whereas in acetonitrile, benzene and chloroform self-aggregation of s-PMMA practically does not take place, which is in agreement with the results of IR spectroscopy, osmometry and viscometry (ref. 22,54,102).
IR spectroscopy and X-ray diffraction
indicate that ordering of s-PMMA also takes place in 1,2-dichloroethane (ref. 115) and in diethyl ketone and chloroacetone (ref. 22,100,101). Aggregation of conventional PMMAis cited in p-xylene and in butyl chloride (ref. 53,55). T h e f o r m a t i o n of t h e PMMA s t e r e o c o m p l e x w a s a l s o s t u d i e d i n m i x e d solvents.
Sedimentation measurements have shown that the stereocomplex
e x i s t s i n m i x t u r e s of D M F / b e n z e n e a n d t h a t t h e s t e r e o c o m p l e x f r a c t i o n i n c r e a s e s w i t h i n c r e a s i n g c o n t e n t of DMF ( r e f . 48), w h i c h i s i n a g r e e m e n t w i t h t h e r e s u l t s of NMR s p e c t r o s c o p y
(cf. T a b l e 4).
T h e k i n e t i c s of
stereoeomplex formation was studied by light scattering
i n a m i x t u r e of
DMF/CC14and it w a s f o u n d t h a t e v e r y time t h e s t e r e o c o m p l e x a g g r e g a t e s t h i s m i x t u r e a r e l i g h t e r a n d s m a l l e r t h a n i n DMF a l o n e ( r e f . 45).
in
The results
of t h e m e a s u r e m e n t of p o l a r i z e d l u m i n e s c e n c e h a v e s h o w n t h a t i n d i l u t e s o l u t i o n s i n a m i x t u r e of D M F / c h l o r o f o r m , s t e r e o c o m p l e x d e c o m p o s i t i o n t a k e s p l a c e i n a n a r r o w r a n g e of s o l v e n t c o m p o s i t i o n (35-50 v o l t of c h l o r o f o r m ) ,
129 confirming the cooperative character s t e r e o c o m p l e x ( r e f . 58}.
of t h e i n t e r m o l e c u l a r b o n d s in t h e
B a s e d o n v i s c o m e t r i c a n d NMR m e a s u r e m e n t s , Liu a n d
Liu {ref. 65) f o u n d t h a t t h e s t e r e o c o m p l e x is n o t f o r m e d in a c e r t a i n c o m p o s i t i o n r a n g e of a m i x t u r e of a c e t o n i t r i l e / b e n z e n e ,
in s p i t e of t h e f a c t
t h a t it is f o r m e d i n t h e s i n g l e c o m p o n e n t s of t h i s mixed s o l v e n t . behavior was observed
A similar
b y Katime e t al. ( r e f . 51) f o r t h e s t e r e o c o m l e x in a
m i x t u r e of a c e t o n i t r i l e / C C 1 4 a n d a c e t o n i t r i l e / b u t y l c h l o r i d e strongly complexing solvents} and for aggregates m i x t u r e of C C 1 4 / b u t y l c h l o r i d e {ref. 55}.
(i.e, f o r m i x t u r e s of
of c o n v e n t i o n a l PMMA in a
The authors
interpret
t h i s e f f e c t in
t e r m s of e x c e s s G i b b s e n e r g y , w h e r e i n c o m p a t i b i l i t y o f t h e c o m p o n e n t s o f t h e c o s o l v e n t m i x t u r e l e a d s to p r e f e r e n c e to " d i s s o l u t i o n " of PMMA a g g r e g a t e s
of t h e p o l y m e r - s o l v e n t i n t e r a c t i o n a n d (ref. 51,55,122).
H o w e v e r , it s h o u l d be
n o t e d t h a t o u r p r e l i m i n a r y r e s u l t s o b t a i n e d b y m e a n s of NMR a n d IR spectroscopy
do n o t i n d i c a t e d e c o m p o s i t i o n of t h e p r i m a r y o r d e r of t h e
s t e r e o c o m p l e x i n c o s o l v e n t m i x t u r e s ( r e f . 123}. only the secondary hindered
process
We h o l d a s m o r e p r o b a b l e t h a t
{i.e., a g g r e g a t i o n of s t e r e o c o m p l e x p a r t i c l e s } i s
in c o s o l v e n t m i x t u r e s a n d t h i s i s a l s o in a g r e e m e n t w i t h t h e r e s u l t s
of DSC a n a l y s i s {ref. 96}. The e x p l a n a t i o n of the m e c h a n i s m b y which v a r i o u s s o l v e n t s promote or h i n d e r e t e r e o a s s o c l a t i o n in n o t q u i t e c l e a r s o f a r . aggregation
Some a u t h o r s
explain
of PMMA b y t h e t e n d e n c y of s o m e p o l a r s o l v e n t s {e.g.,
a c e t o n i t r i l e ) to s e l f - a s s o c i a t e ( l i q u i d o r d e r ) , w h i c h h i n d e r s w i t h t h e p o l y m e r ( r e f . 51,55,122}.
their interaction
However, s u c h a " p a s s i v e " role of the
s o l v e n t d o e s n o t e x p l a i n t h e c o m p l e t e l y d i f f e r e n t e f f e c t o f a c e t o n i t r i l e in s t e r e o c o m p l e x f o r m a t i o n a n d in s e l f - a g g r e g a t i o n
of s-PMMA.
On t h e o t h e r
h a n d , t h e r e e x i s t s t u d i e s a s s u m i n g a n " a c t i v e " r o l e of t h e s o l v e n t e v e n f o r ordering
o f s-PMMA i n t h e s o l i d s t a t e ( r e f . 24,100,101}.
In our opinion, the solvent can affect aggregation
of PMMA b y two
m e c h a n i s m s (ref. 22): 1} c h a n g e s of t h e c o n f o r m a t i o n a l s t r u c t u r e stereoregular
sequences
(conformer energy
of
d i f f e r e n c e s t h e n also become
i m p o r t a n t } w i t h p r o m o t i o n o r h i n d r a n c e of s t e r i c a l l y c o m p l e m e n t a r y i n t e r a c t i o n s ; a n d 2) h i n d r a n c e
(or p r o m o t i o n } of s t e r e o a s s o c i a t i o n b y s p e c i f i c
interactions with certain functional groups.
Concerning the first mechanism,
the e f f e c t of s o l v e n t on the conformational s t r u c t u r e has actually been observed
( e s p e c i a l l y o f s-PMMA}
f r o m 13C a n d 1H NMR r e l a x a t i o n m e a s u r e m e n t s a n d
b y m e a n s o f NMR s h i f t r e a g e n t s
( r e f . 29,124).
The e f f e c t of s o l v e n t on t h e
c o n f o r m a t i o n a l e q u i l i b r i u m o f s-PMMA i n s o l u t i o n i s i n d i c a t e d b y t h e r e s u l t s of IR s p e c t r o s c o p y
( r e f . 21,22,29}.
i n t e r a c t i o n s o f PMMA e s t e r g r o u p s
For the second mechanism, specific (these groups
are i m p o r t a n t in
s t e r e o a s e o c i a t i o n o f PMMA; s e e l a t e r o n i n t h e f o l l o w i n g p a r t } w i t h b e n z e n e molecules have been described
in t h e l i t e r a t u r e
( r e f . 125,126}.
The
130 experimental formed,
finding
that
in benzene
while the stereocomplex
interactions
of stereocomplex
unfavorable
effect of solvent,
self-aggregates
(cf. P a r t
circumstance
that
formation
takes
hydrogen
bonds
proved
Rehage
are
sufficient
while the weaker
neither
self-aggregation
place in chloroform between
between
chloroform
at-PMMA.
of stereoregular
LOCAL
STRUCTURE
A. C h a r a c t e r
to c o m p e n s a t e
for the
of s-PMMA
for this end.
Similarly, the
with the existence
carbonyls
which
have
of been
I n t h e s a m e w a y {i.e., b y c o m p l e x PMMA e s t e r
clarification
OF AGGREGATED
groups},
on association
Kock and of cross-linked
of the effect of solvent
PMMA d e s e r v e s
of the interactions
the stronger
of s-PMMA nor stereoeomplex
molecules and
However, a complete
so that
interactions
molecules and
( r e f . 127}.
solvent
of s-PMMA are not
could be connected
( r e f . 63) e x p l a i n t h e e f f e c t o f s o l v e n t
aggregation
VI.
type
V-C) a r e i n s u f f i c i e n t
in small molecules
formation
self-aggregates
is, could be explained
further
SEQUENCES
of functional
on the
study.
OF PMMA
groups
responsible
for
a~re~ation Concerning their
mutual
the
question
interaction
a s to w h i c h f u n c t i o n a l
f o r PMMA s t e r e o c o m p l e x
can be found
in the literature.
stereocomplex
is formed
groups
o f i-PMMA a n d
stereocomplex also formed
Liquori etal.
in consequence s-PMMA, thus
in polar solvents. in nonpolar
the basic role of ester self-aggregation Conclusive
results
( r e f . 104,106}.
groups,
it w a s f o u n d resolution bands pulse
and
of another
one of about
have
measured
of the polymer
and
in
o f i-PMMA a n d is essential;
From conventional
have
and
increases,
spinning spinning
whereas
protons shown
speeds speed,
the intensity
speed
(3"2:3).
that
of about
yield a high
{Fig. 17).
~-CH 3
The results
the spectrum
of this
and system
F r o m F i g . 17, i t
the intensity
o f t h e CH 2
o f t h e OCH 3 b a n d
does
m : ICH2+~-CH3/IOCH 3
t o 2.8 a t ~r = 5 kHz, w h e r e a s
of
of the
300 Hz w i d t h
1H MAS NMR s p e c t r a
At t h e s a m e t i m e , t h e r a t i o o f t h e i n t e n s i t i e s spinning
see Part
1H NMR s p e c t r a
o f t h e OCH3, CH 2 a n d
of a band
15-20 kHz width.
at various
with increasing
is
indicating
b y NMR s p e c t r o s c o p y
with a mixture
of respective
consists
with increasing
increases
formation
presented
in which the intensities
can be seen that
not.
the of ~-CH 3
of the
accumulated
(lower stereoregularity
NMR m e a s u r e m e n t s
part
a-CH 3 bands
were
was performed
to t h e n u m b e r
broad=line
that
the stereocomplex
a t 2 5 " C p = 40% (i.e., 60% o f m o n o m e r u n i t s
associated
been
gradually
r a t i o r = ( Y s / X i ) = 2.
NMR s p e c t r u m
correspond
that
by
opinions
interactions
the formation
both in stereocomplex
in this respect
The analysis
that
responsible
various
s-PMMA.
s-PMMA of lower stereoregularity VII-A) at the weight
explaining
evidence
are
( r e f . 33) a s s u m e d
of hydrophobie
After the finding
solvents,
of i- and
groups
formation,
the
131
-..--I C H 2 - - C - - L
(A)
...
(c)
Jn
(c)
(a)
/~
i
6
7
8
9
1'0
~in ppm
10
t i n ppm
(c)
(B) (a)
A 6
L 7
i 8
9
(c)
7
8
10
g
in ppm
Fig. 17. 1H MAS NMR s p e c t r a of t h e m i x t u r e i-PMMA (I : 97%; H : 3%) + s-PMNA (S = 65%; H = 31.5%) (1:2) in C6D 6 m e a s u r e d a t 60 MHz, 25"0, a n d d i f f e r e n t s p i n n i n g f r e q u e n c i e s Vr; (A): (u r ~ 1.5 kHz; (B): v r ~ 3.5 kHz; (C): v r ~ 5 kHz ( r e f . 104). value corresponding
to t h e n u m b e r of p r o t o n s i s 5 / 3 = 1.67.
As in t h e 1H
MAS NMR e x p e r i m e n t , we s e e o n l y t h e s p e c t r u m o f t h e u n a s s o c i a t e d p a r t of t h e p o l y m e r p l u s t h o s e l i n e s of t h e a s s o c i a t e d p a r t w h i c h h a v e b e e n n a r r o w e d b y t h e s p i n n i n g ; t h e a b o v e r e s u l t c a n be e x p l a i n e d s o t h a t o n l y t h e l i n e s of CH2 a n d ~-CH 3 g r o u p s of t h e a s s o c i a t e d p o l y m e r u n d e r g o
narrowing
by magic angle spinning.
By a s i m p l e c a l c u l a t i o n , it c a n b e s h o w n t h a t t h e
v a l u e m = 2.8 c o r r e s p o n d s
to t h e s i t u a t i o n w h e r e t h e 1H MAS NMR s p e c t r u m
r e v e a l s all t h e p r o t o n s o f t h e CH2 a n d =-CH 3 g r o u p s non-associated)
w h e r e a s t h e OCH 3 b a n d c o r r e s p o n d s
unassociated segments.
(both associated and o n l y to p r o t o n s of t h e
132 A s i m i l a r s i t u a t i o n w a s o b s e r v e d a l s o i n 13C NMR s p e c t r a m e a s u r e d w i t h t h e d e c o u p l i n g i n t e n s i t y ~H2/2~, ~ 5 kHz, w h e r e t h e i n t e g r a t e d t h e OCH 3 b a n d a m o u n t s to o n l y 79% of t h e q u a t e r n a r y a-CH 3 a n d CH2 c a r b o n s
i n t e n s i t y of
c a r b o n a n d of t h e
(a s a m p l e w i t h p -- 30% w a s s t u d i e d ) .
These results
i n d i c a t e t h a t t h e b a n d of 15-20 kHz w i d t h w h i c h c a n n o t b e n a r r o w e d b y m a g i c a n g l e r o t a t i o n a t v r ~ 5 kHz o r b y d i p o l a r d e c o u p l i n g a t 7H2/2~ = 5 kHz c o r r e s p o n d s corresponds
to OCH 3 g r o u p s , w h e r e a s t h e b a n d of 300 Hz w i d t h
to CH2 a n d ~-CH 3 p r o t o n s .
As t h e m o b i l i t y of t h e OCH 3 m e t h y l
g r o u p s i s r e l a t i v e l y h i g h e v e n in solid PMMA, it m u s t b e c o n c l u d e d t h a t in t h e s t e r e o c o m p l e x , t h e m o b i l i t y of t h e w h o l e e s t e r g r o u p i s g r e a t l y indicating that association takes place primarily through
reduced,
i n t e r a c t i o n of e s t e r
groups. C o n s i d e r a b l e h i n d r a n c e of e s t e r g r o u p m o t i o n i n t h e s t e r e o c o m p l e x is a l s o confirmed by the observed
n e g a t i v e v a l u e s of o p t i c a l a n i s o t r o p y
(ref. 42).
N e g a t i v e v a l u e s of o p t i c a l a n i s o t r o p y w e r e a l s o d e t e r m i n e d i n s e l f - a g g r e g a t e s of i-PMMA; a l s o , i n t h i s c a s e , t h e o b s e r v a t i o n w a s i n t e r p r e t e d ordering
of e s t e r g r o u p s a n d t h e i r c o o p e r a t i v e i n t e r a c t i o n s
by specific
( r e f . 42,46,62).
H i n d r a n c e of e s t e r g r o u p m o b i l i t y b y s t e r e o a s s o c i a t i o n i s a l s o i n d i c a t e d b y t h e r e s u l t s of d y n a m i c a l - m e c h a n i c a l m e a s u r e m e n t s , s h o w i n g t h a t i n s a m p l e s prepared
b y r a d i c a l p o l y m e r i z a t i o n of MMA p r o c e e d i n g in t h e PMMA
s t e r e o c o m p l e x g e l (or in i-PMMA " s o l u t i o n " ; in b o t h c a s e s , MMA s i m u l t a n e o u s l y s e r v e d a s " s o l v e n t " ) , t h e E - p r o c e s s i s d i s p l a c e d to h i g h e r t e m p e r a t u r e s 30-40"C) ( r e f . 85). the ordered
(by
T h e i m p o r t a n t r o l e of e s t e r g r o u p s i n t h e f o r m a t i o n of
stereocomplex structure
is also indicated by the viscometric
r e s u l t s of S h a c h o v s k a y a e t al. ( r e f . 72), i n d i c a t i n g t h a t in m i x t u r e s of i-PMMA w i t h MMA/MAA c o p o l y m e r s , t h e r e p l a c e m e n t of t h e e s t e r g r o u p s of t h e s-component by carboxyl groups
perturbs
t h e s t e r i c c o m p l e m e n t a r i t y of t h e
macromolecules. In the a bove cited p a p e r s ,
stereocomplex formation is supposed
to t a k e
p l a c e i n c o n s e q u e n c e of m u t u a l i n t e r a c t i o n s of t h e e s t e r g r o u p d i p o l e s of i a n d s-PMMA.
A somewhat d i f f e r e n t view c o n c e r n i n g the c h a r a c t e r
of
f u n c t i o n a l g r o u p i n t e r a c t i o n s l e a d i n g to s t e r e o c o m p l e x f o r m a t i o n w a s p u b l i s h e d b y C h a l l a e t al. ( r e f . 36,94,100).
Based on the finding that the
s t e r e o c o m p l e x i s f o r m e d b e t w e e n t h e i - c o m p o n e n t of PMMA a n d t h e s - c o m p o n e n t of e i t h e r PMMA, PiBMA o r PMAA a n d t h a t all t h e s e stereocomplexes exhibit the same X-ray pattern,
these authors
assume that
s t e r e o a s s o c i a t i o n t a k e s p l a c e i n c o n s e q u e n c e of i n t e r a c t i o n s of i-PMMA e s t e r g r o u p s w i t h t h e =-CH 3 g r o u p s of t h e s y n d i o t a c t i c c o m p o n e n t . T h e i m p o r t a n c e of e s t e r g r o u p d i p o l e i n t e r a c t i o n s i n s-PMMA self-aggregation
i s i n d i c a t e d b y t h e s p l i t t i n g of t h e C=0 s t r e t c h i n g
into three components with wavenumbers
vibration
e q u a l i n t h e solid s t a t e a n d i n
133 solutions
and
F i g . 18 a r e {a) a n d
of different
shown
120 rain (b) a f t e r
w h i c h all a g g r e g a t e s spectrum fraction
higher
self-aggregation
wavenumber
22,102,111,115).
indicating
( r e f . 111).
The absolute
determined
after
units
conclusion
that
(about
-
I
s-PMMA
in aggregated
of ordered
vibration
s-PMMA
s-PMMA in solution
i n IR s p e c t r a
are
of associated
monomer
( s e e T a b l e 3); t h i s l e a d s
one half) of the ester
I
at a
a t 1727 c m - 1 ( r e f .
in ordered
groups
It can
by a new band
bands
monomer units
I
(b) a f t e r
of the fraction
f r o m NMR s p e c t r a
I
groups
of ester
of the carbonyl
only a part
band
at as the
i n F i g . 18c.
o f t h e C--0 s t r e t c h i n g
of the fraction
the values
(immobilized)
c a .D
of ester
from spectrum
is shown
by a weak
In
of the aggregated
in this range
for the splitting
values
separation
p determined
aggregated
is exhibited
close contact
lower than
111).
a t 2 5 " C , 2 rain
(a) m a y b e r e g a r d e d
obtained
component)
dipole coupling
sequences,
(ref.
measured
T h e IR s p e c t r u m
spectrum
(1742 c m - 1 ) a n d
The reason
is the transition
spectrum
s-PMMA.
of the non-aggregated
that
IR s p e c t r a
c o o l i n g f r o m 100"C {i.e., f r o m a t e m p e r a t u r e
of s-PMMA (difference
considerably
in Raman and
of s-PMMA in toluene
are decomposed);
of non-aggregated
subtraction be seen
activity
IR s p e c t r a
to t h e
groups
in
are in close contact.
I
J
I
I
i
b
tO
..Q <[
,.
I
1790
I
I
1750
l
I
1710
I
I
,
-I 1670
cm Fig. 18. R a n g e of C:0 stretching vibrations in IR spectra of s - P M M A (S : 89.5%; H : 8.6~) in toluene m e a s u r e d at 25°C a n d 2 rain (a) or 120 rain {b) after cooling from 100°C. S p e c t r u m (c) s h o w s the range of C:0 stretching vibrations in IR spectrum of the aggregated fraction of s - P M M A (ref. 111).
134 Negative
values
mobility of ester The finding ordered ester
of optical anisotropy
groups that
interactions
structures
( r e f . 128).
the frequency
differences
coupling molecular
order
ester
Av b e t w e e n
and
of methyl
acetate
of the aggregates
structure
of i- and
diffraction
Liquori
and
of stereoregular
to these
structure
does
situated
above
mentioned,
and
diffractogram,
From energy
Boscher
assumes
form a double
is surrounded i/s
results
s-PMMA. original
structure
with a change
indicates
conformation
differs
(ref. 10-12).
of a slightly
found
theoretically somewhat
that
distorted
that
from Based i-PMMA 8/I
the i- and
radius
of ref. i00)
assume
the
a 60/4 helix. yield
of s-PMMA in the
the formation
Analysis
conformational that
structure
in stereocomplex
by Grigoreva
from the conformation
of the
of the stereocomplex
of s-PMMA is changed
proposed
(they
the lowest conformation
for s-PMMA forming
structure
of the backbone
chain conformation
with a glide plane,
only slightly
in
o f i-PMMA i n t h e s t e r e o c o m p l e x ,
that
M i h a i l o v e t al. ( r e f . 113) a s s u m e extended
deviating
b y m e a n s o f IR s p e c t r o s c o p y .
860 c m - I
chains
approximation)
(especially
on the conformational
a t 843 a n d
is connected
have
diffraction
more direct
doublet
the
with both
e t al. ( r e f . 100) c o n c l u d e d
authors
on the conformational
were obtained
to t h e c h a i n a x i s , below this plane.
and with the assumption
information
stereocomplex
to c o r r e s p o n d
propose
helical structure,
a 30/4 helix and
of X-ray
the
much from the
h e l i x i n w h i c h a n i-PMMA c h a i n o f s m a l l e r
these
f o r i-PMMA f o r m i n g
While the results
groups
studies
by an s-PMMA chain of larger
= I/2),
that
not differ
all e s t e r
the conformation
calculations
by
s-PMMA in the stereocomplex
the more recent
c h a i n f o r m (in t h e s t a g g e r e d
PMMA
was studied
with the glide plane parallel
o f i-PMMA i n t h e d o u b l e
in the stereocomplex
energy
that
Based on a fiber
time was assumed
authors,
t h e f o r m o f a 1 0 / 1 h e l i x ; i.e., i n a c o n f o r m a t i o n
stoichiometry
shown
in the
o f IR s p e c t r o s c o p y .
i-PMMA w h i c h a t t h a t
w i t h all ~ - C H 3 g r o u p s As we have already
radius
of
short-range
e t al. ( r e f . 33) c a m e t o t h e c o n c l u s i o n
According
has a conformational
s-PMMA chains
have
generates
s-PMMA chains
of pure
to t h e 5 / 1 h e l i x .
helix.
of model
isotropic
in the self-aggregates
conformation
also on a fiber
and
of
dependences
in simple esters
o f i-PMMA i n t h e s t e r e o c o m p l e x
the extended
of Raman spectra
the anisotropic
conformation
crystallization
l e a d to t h e f o r m a t i o n
of the concentration
vibration
of s-PMMA chains
of X-ray
diffractogram,
groups
structure
The conformational
the methods
groups
hindered
a t - P M M A ( r e f . 63).
in the liquid state,
B. C o n f o r m a t i o n a l
stereocomplex
considerably
also by studies
Measurements
o f t h e C=0 s t r e t c h i n g
of methyl
indicate
of crosslinked
of ester
was verified
systems
components
in associates
of
formation,
the
to a c o n f o r m a t i o n
e t al. ( r e f . 15); t h i s
proposed
i n r e f . 33.
135 H o w e v e r , r e c e n t d e t a i l e d a n a l y s i s h a s s h o w n t h a t t h e b a n d a t 860 cm -1, t h e i n t e n s i t y of w h i c h s t r o n g l y i n c r e a s e s in s t e r e o c o m p l e x f o r m a t i o n ( b o t h in s o l u t i o n a n d in t h e solid s t a t e ) , c o r r e s p o n d s to l o n g s - s e q u e n c e s in t h e e x t e n d e d c h a i n c o n f o r m a t i o n of t h e b a c k b o n e (in t h e s t a g g e r e d a p p r o x i m a t i o n ) ( r e f . 21,22; s e e Fig. 19a).
S e l f - a g g r e g a t i o n of s-PMMA in s o l u t i o n also l e a d s
to a n i n c r e a s e in t h e f r a c t i o n of long s - s e q u e n c e s in t h e e x t e n d e d c h a i n c o n f o r m a t i o n a n d t h i s t r e n d is m a i n t a i n e d also in solid s-PMMA i s o l a t e d from t h e s e s o l u t i o n s u n d e r c o n d i t i o n s w h e r e d e c o m p o s i t i o n of t h e a g g r e g a t e s d o e s n o t t a k e p l a c e ( r e f . 22).
In comparison with n o n - a g g r e g a t e d amorphous
s-PMMA w h e r e t t c o n f o r m a t i o n a l f o r m s also d o m i n a t e ( a c c o r d i n g to t h e o r e t i c a l c a l c u l a t i o n s a n d X - r a y d i f f r a c t i o n ; r e f . 9,17,18) in t h e s t e r e o c o m p l e x a n d in s e l f - a g g r e g a t e s , t h e e x t e n d e d c h a i n c o n f o r m a t i o n of s-PMMA p e r s i t s o v e r much l o n g e r d i s t a n c e s .
CH
c
o CH3
(o}s-PMMA
lb) OMTMGA
Fig. 19. E x t e n d e d c h a i n c o n f o r m a t i o n a l s t r u c t u r e of s-PMMA (a) a n d t h e e n e r g e t i c a l l y m o s t f a v o r e d c o n f o r m e r of DMTMGA (b) ( r e f . 108). T h e results of X-ray diffraction indicate that the conformational structure of s - P M M A
prepared b y solvent-induced crystallization (in vapors of
aggregation-promoting of s - P M M A
solvents) does not differ m u c h from the conformation
in the stereocomplex; K u s u y a m a
74/4 helix of large diameter.
et al. (ref. 24) propose for it a
At the same time, however, the fiber period 73.6
/~ of the 60/4 helix of s - P M M A
in the stereocomplex is roughly twice as long
as the fiber period (35.4 ~) a s s u m e d for the 74/4 helix in the ordered s-PMMA PMMA
alone (ref. 24,100).
It is clear that the conformational structures of
segments in helices with a large n u m b e r
of m o n o m e r
units per turn
(e.g., 60/4 or 74/4) can be generated from forms not differing m u c h staggered tt form.
from the
It m a y therefore be stated that the results of
conformational analysis obtained from IR spectra are in agreement with such helical b a c k b o n e structure.
In this sense, it is then possible to describe the
136 IR b a n d band
of long s-sequences
corresponding
I n t h e IR s p e c t r a for studies
found.
This is evidently bands
chain conformation
a conformationally
of the conformational due
structure
that
deuterated
o f PMMA ( r e f . 129) w a s a c o n f o r m a t i o n a l l y
analogs
crystalline
stereocomplex
X-ray
and
i-PMMA a n d
which is not present
in solutions
analysis
in the spectra
stating
o f i-PMMA. that
similar conformational
structure
of long sequences
not detected
in solutions
In addition the ester
groups
that
that
the mutual
energetically
in interaction
s-sequences be assumed
of
t h e i-PMMA c h a i n s
have
i-PMMA.
to
Contrary
a
structure
structure,
was
the orientation
cis orientation
o f C--0 a n d
( r e f . 130; s e e F i g . 1 9 b ) .
VIII-A), cis orientation
o f s - P M M A ( s e e F i g . 19a). by the results
of
C-CH 3 b o n d s
Based on the
w i t h i - o r s - P M M A , DMTMGA b e h a v e s
( r e f . 108; s e e P a r t
is supported
solid
the results
I n DMTMGA ( t h e d i m e r m o d e l o f
to exist also in s-PMMA chains
self-aggregates
band
of
of amorphous
confirms
with tt conformational
conformational
h a s to b e c o n s i d e r e d .
PMMA), it w a s f o u n d
of
o f i-PMMA.
to t h e b a c k b o n e
is the most favored finding
as in crystalline
sensitive
i n IR s p e c t r a
i n IR s p e c t r a
s-PMMA, the presence
of s-PMMA.
of the corresponding
This finding
in the stereocomplex,
band was not
of the stereocomplex
o f 800 c m - I , w h i c h i s p r e s e n t
deuterated
i-PMMA a n d
o f t h e IR s p e c t r a
bands
completed
in the range
sensitive
the conformationally
by stronger
Only in a recently
detected
( r e f . 22).
o f i-PMMA c h a i n s
to t h e c i r c u m s t a n c e
o f i-PMMA a r e o v e r l a p p e d study
a t 860 c m - 1 a s a
of the s-PMMA backbone
of the stereocomplex,
suitable
sensitive
in extended
to a helical structure
of ester
groups
in the stereocomplex In the latter
of the studies
s i m i l a r l y to
case,
of deuterated
may
and in
this assumption
s-PMMA analogs
( r e f . 116). As mentioned self-aggregates, appearance interesting one band
in the previous
paragraph,
mutual ordering
of ester
of a new carbonyl that
t h e IR s p e c t r u m
in the range
of s-PMMA in solutions
22).
This indicates
that
VII.
AND MOBILITY
Measurements s-PMMA
wavenumber.
vibrations,
aggregation
the mutual arrangement
is different
of s-PMMA
is manifested
by the
However, it is
of s-PMMA in the stereocomplex
where
self-aggregates
A. Effect of aggregation
at higher
o f C=0 s t r e t c h i n g
band
ORDERING
band
i n IR s p e c t r a groups
from that
exhibits
corresponding
does not take o f C=0 b o n d s
only
to t h e
place
(ref.
in s-PMMA
in the stereocomplex.
OF CHAINS
IN A G G R E G A T E S
OF PMMA
on segmental mobility of the chains
of 1H N M R
relaxation times T 2 in gels of mixtures of i- a n d
in C 6 D 6 (conc. 10%) have s h o w n
that in these systems,
present with the relaxation times T 2 : 36 ms, 0.9 m s a n d T h e first of these corresponds
protons are
15 /Js (ref. 104).
to relaxation times of pure i - P M M A
or s - P M M A
137
in C6D 6 s o l u t i o n a n d a g r e e s w i t h t h e l i n e w i d t h s in h i g h r e s o l u t i o n NMR s p e c t r a ; it i s a s s i g n e d shorter
to p r o t o n s in n o n - a s s o c i a t e d
u n i t s of PMMA.
relaxation times {indicating severely hindered
T h e two
mobility} a r e a s s i g n e d
to p r o t o n s of a s s o c i a t e d s e g m e n t s a n d t h e y a g r e e w i t h t h e s h a p e of t h e b r o a d - l i n e NhIR s p e c t r u m w h i c h c o n s i s t s of b a n d s of 300-400 Hz a n d of 15-20 kHz w i d t h .
As a l r e a d y m e n t i o n e d in P a r t VI-A, t h e b a n d of 15-20 kHz w i d t h
is a s s i g n e d
to e s t e r m e t h y l g r o u p s ~ w h e r e a s t h e b a n d of 300-400 Hz w i d t h is
assigned
to CH2 a n d ~-CH 3 p r o t o n s .
Also, w i t h t h e s e l f - a g g r e g a t e s
of
s-PMMA in t o l u e n e - d 8, s i m i l a r l i n e - w i d t h v a l u e s (A~ = 500 Hz} w e r e f o u n d f o r the backbone proton groups
( r e f . 110).
M e a s u r e m e n t s of 1H MAS N/*IR s p e c t r a a t v a r i a b l e t e m p e r a t u r e s NMR s p e c t r a
with strong
a n d of 13C
p r o t o n d e c o u p l i n g h a v e s h o w n t h a t with r e s p e c t
to
t h e b r o a d e n i n g o f t h e b a n d s of CH2 a n d ~-CH 3 p r o t o n s ~ t h e s y s t e m s s t u d i e d c a n be d i v i d e d i n t o two g r o u p s .
T h e f i r s t g r o u p is f o r m e d b y t h e m i x t u r e s
o f t h e s o l u t i o n s of i - a n d at-PMMA in C6D6~ w h e r e t h e v a l u e s of t h e a s s o c i a t e d f r a c t i o n a r e r e l a t i v e l y low (p = 30-40%} a n d w h e r e t h e m e n t i o n e d m e t h o d s l e a d to t h e n a r r o w i n g of b a n d s of 300-400 Hz w i d t h ( r e f . 104,106}. I n 1H MAS NMR s p e c t r a of t h e s e s y s t e m s , t h e b a n d s of p r o t o n s of a-CH 3 a n d CH2 g r o u p s
in a s s o c i a t e d s e g m e n t s h a v e the same width a s the c o n v e n t i o n a l l y
m e a s u r e d b a n d s of t h e p r o t o n s in n o n - a s s o c i a t e d
s e g m e n t s o r in s o l u t i o n s
w h e r e t h e a s s o c i a t i o n of PMMA d o e s n o t t a k e p l a c e . ~-CH 3 a n d frequency
CH2 g r o u p s
undergo
(in all t h e s e c a s e s } m o t i o n s a t a s i m i l a r
a n d t h a t t h e a s s o c i a t e d s e g m e n t s t h e r e f o r e c a n n o t be r e g a r d e d
static systems.
as
T h e w i d t h of 300-400 Hz e x h i b i t e d b y t h e b a n d s of a-CH 3 a n d
CH2 p r o t o n s i n c o n v e n t i o n a l l y m e a s u r e d s p e c t r a near-static
This indicates that the
is in t h i s c a s e limited b y
d i p o l a r i n t e r a c t i o n s w h i c h a r e a c o n s e q u e n c e o f t h e r e s t r i c t i o n of
t h e m o t i o n of t h e s e g r o u p s
in space~ i n c o n n e c t i o n w i t h t h e m u c h m o r e
s e v e r e r e s t r i c t i o n of t h e m o t i o n of t h e OCH3 g r o u p s .
All t h e s e d a t a f r o m t h e
m e a s u r e m e n t s o f l i t NMR s p e c t r a ~ t o g e t h e r w i t h t h e e v i d e n c e a b o u t t h e e x i s t e n c e of a s s o c i a t e d a n d n o n - a s s o c i a t e d
segments and the similarity with
t h e NMR b e h a v i o r of s w o l l e n g e l s of c h e m i c a l l y c r o s s l i n k e d p o l y m e r s , a r e c o m p a t i b l e w i t h t h e i d e a t h a t t h e s t e r e o c o m p l e x e s w i t h p = 30-40% h a v e t h e structure
of a n e t w o r k with the a s s o c i a t e d s e g m e n t s f o r m i n g the c r o s s l i n k
p o i n t s (Fig. 20a) {ref. 104,106,120}. The network structure
of t h e s t e r e o c o m p l e x o f PMMA w a s a l s o p r o p o s e d
by
R e h a g e e t al. ( r e f . 52,66p88~89~91) o n t h e b a s i s of v i s c o m e t r i c a n d dynamico-mechanical measurements.
It s h o u l d be mentioned t h a t also in t h e s e
s t u d i e s ~ g e l s of m i x t u r e s of i - a n d at-PMMA i n o - x y l e n e a n d i n t o l u e n e w e r e
investigated.
138
Fig. 20. S c h e m a t i c r e p r e s e n t a t i o n of t h e s t r u c t u r e s of PMMA s t e r e o c o m p l e x e s in s o l u t i o n s : (a) s t e r e o c o m p l e x w i t h p = 30-40% ( n e t w o r k model}; (b) s t e r e o c o m p l e x w i t h p ~ 95% ( d o u b l e h e l i c a l model} ( r e f . 106}. M i x t u r e s of s o l u t i o n s of i - a n d s-PMMA i n C6D 6 o r i n CD3CN w h e r e t h e v a l u e of t h e a s s o c i a t e d f r a c t i o n p is h i g h (more t h a n 80%) ( s i m i l a r l y a s t h e self-aggregates
o f s-PMMA i n t o l u e n e - d 8 ; p = 85%) e x h i b i t e d c o m p l e t e l y
d i f f e r e n t b e h a v i o r in NMR e x p e r i m e n t s ( r e f . 106,110).
C o n t r a r y to t h e
s t e r e o c o m p l e x w i t h p = 30-40%, s p i n n i n g a t t h e m a g i c a n g l e h e r e d o e s n o t a f f e c t t h e s h a p e of t h e IH NMR s p e c t r a ; a l s o , t h e p r o t o n d e c o u p l i n g w i t h 7H2/2w I 5 kHz d o e s n o t a f f e c t t h e s h a p e of t h e 13C NMR s p e c t r a of t h e s e systems.
T h i s i n d i c a t e s t h a t f o r t h e c o m p l e x e s w i t h p a b o v e 80% a n d a s well
as for the self-aggregates
of s-PMMA, t h e l i n e w i d t h ~ 400 Hz in 1H NMR
s p e c t r a is not limited by r e s i d u a l n e a r - s t a t i c s h a p e of t h i s b a n d s h o u l d r a t h e r
be d e s c r i b e d
with an effective correlation frequency a b o u t two o r d e r s
dipolar interactions but that the by motion isotropic in sp a c e
of 106-107 Hz; t h i s v a l u e is l o w e r b y
of m a g n i t u d e t h a n t h e c o r r e l a t i o n f r e q u e n c y
s-PMMA ( r e f . 106,110).
The retardation
of u n a s s o c i a t e d
of t h e m a i n c h a i n s e g m e n t a l m o t i o n is
e v i d e n t l y c a u s e d b y t h e h i g h d e n s i t y of c o n t a c t s (Fig. 20b). Also, t h e r e s u l t s o b t a i n e d b y t h e m e t h o d of p o l a r i z e d l u m i n e s c e n c e characterizing
the c h a i n mobility in s t e r e o c o m p l e x a g g r e g a t e s
DMF s o l u t i o n s ( r e f . 58) a r e i n v e r y
in v e r y d i l u t e
g o o d a g r e e m e n t w i t h t h e NMR r e s u l t s .
By
t h i s m e t h o d , it w a s f o u n d t h a t t h e m o b i l i t y of PMMA c h a i n s in t h e s t e r e o c o m p l e x is l o w e r b y a b o u t two o r d e r s n o n - a s s o c i a t e d PMMA.
of m a g n i t u d e t h a n f o r
E v e n t h e a b s o l u t e v a l u e s of t h e r e l a x a t i o n time Vw
d e t e r m i n e d f o r t h e s t e r e o c o m p l e x b y t h e m e t h o d of p o l a r i z e d l u m i n e s c e n c e a r e e q u a l to t h e v a l u e s of t h e c o r r e l a t i o n time Tc d e t e r m i n e d f o r t h e a s s o c i a t e d s e g m e n t s f r o m NMR s p e c t r a retardation
(v w a n d Tc a r e a b o u t 100 n s ) .
The pronounced
of t h e s e g m e n t a l m o b i l i t y of c h a i n s i n t h e s t e r e o c o m p l e x of PMMA
a n d i n s-PMMA s e l f - a g g r e g a t e s
w i t h a h i g h d e n s i t y of i n t e r a c t i o n s
indicates a completely different structure
(p £ 80%)
of t h e s e s y s t e m s f r o m t h a t of t h e
s w o l l e n g e l s of c h e m i c a l l y c r o s s l i n k e d p o l y m e r s (c.f. P a r t IV-C).
B. Chain ordering Studies of the stereocomplex of P M M A
and of s - P M M A self-aggregates b y
means of X-ray diffraction and vibrational spectroscopy have indicated that the conformationai s t r u c t u r e and ordering of chains of aggregates in solution
139 is t h e s a m e a s in solid s a m p l e s i s o l a t e d f r o m t h e s e s o l u t i o n s u n d e r preventing
d e c o m p o s i t i o n of t h e a g g r e g a t e s .
X-ray pattern
was observed
conditions
An i d e n t i c a l t y p e of c r y s t a l l i n e
f o r t h e s t e r e o c o m p l e x g e l s in b e n z e n e a n d f o r
solid s t e r e o c o m p l e x s a m p l e s ( r e f . 69).
A l t h o u g h c r y s t a l l i n i t y c o u l d n o t be
d e t e c t e d b y X - r a y d i f f r a c t i o n in c o n c e n t r a t e d
suspensions
of s-PMMA in BAC
( r e f . 38), a c l e a r c o n n e c t i o n b e t w e e n a g g r e g a t i o n of s-PMMA in s o l u t i o n a n d d e v e l o p m e n t of c r y s t a l l i n e s t r u c t u r e ( r e f . 22,38,102).
in solid s-PMMA c o u l d be d e m o n s t r a t e d
S i m i l a r l y , t h e r e s u l t s of IR s p e c t r o s c o p y
(in s e l f - a g g r e g a t e s
of s-PMMA, e s p e c i a l l y t h e e q u a l s p l i t t i n g of t h e c a r b o n y l v i b r a t i o n ) h a v e s h o w n t h a t b o t h i n t h e s t e r e o c o m p l e x a n d in t h e s e l f - a g g r e g a t e s the conformational structure the corresponding proved
of s - P H H A ,
of t h e s - c h a i n s is t h e s a m e in s o l u t i o n s a n d in
solid s a m p l e s (ref. 21,22,102,111).
by electron microscopy, self-aggregation
a f f e c t s t h e m o r p h o l o g y of solid s-PMHA ( r e f . 22). f r o m a c e t o n i t r i l e s o l u t i o n is s t r u c t u r e l e s s
At t h e s a m e time, a s
of s-PMMA in s o l u t i o n a l s o While solid s-PMMA i s o l a t e d
{Fig. 21b), solid s-PMHA i s o l a t e d
from toluene solution exhibits clearly fibrillar character
~a}
{Fig. 21a).
(b)
Fig. 21. Electron micrographs of s - P M M A (S -- 89.5%; H -- 8.5%) films prepared by evaporation of so]vent at room temperature from to]uene (a) and acetonitrile (b) solution (ref. 22). I n o n e of t h e o l d e s t p a p e r s c o n c e r n i n g t h e s t e r e o c o m p l e x of P M M A , e t al. (ref. 33) h a v e p r o p o s e d f o r t h i s s y s t e m a s t r u c t u r a l
Liquori
model w h e r e t h e
s-PMMA c h a i n s in a c o n f o r m a t i o n w i t h a g l i d e p l a n e lie i n " g r o o v e s " f o r m e d b y t h e 5/1 h e l i c e s of i-PMMA c h a i n e s (Fig. 22a).
H o w e v e r , in t h e c o u r s e of
time, e v i d e n c e is a c c u m u l a t i n g w h i c h i n d i c a t e s t h a t t h e f o r m a t i o n o f t h e s t e r e o c o m p l e x i s c o n n e c t e d w i t h t h e i n t e r a c t i o n of i - a n d s - s e q u e n c e s
which
a r e p a r e l l e l o v e r l o n g d i s t a n c e s , w i t h a b a c k b o n e c o n f o r m a t i o n n e a r to "all trans"
( s e e P a r t s V-B, V-C, VI-B, VII-A a n d VIII-B).
observation
Based on the
t h a t i n t h e s t e r e o c o m p l e x w i t h h i g h v a l u e s of t h e a s s o c i a t e d
f r a c t i o n p t h e s e g m e n t a l m o t i o n of t h e c h a i n s i s i s o t r o p i c a n d r e t a r d e d P a r t VII-A), t h e s t r u c t u r e
w a s p r o p o s e d f o r t h e f i r s t time ( r e f . 106; cf. Fig. 20b). diffraction and energy
(cf.
of t h e d o u b l e h e l i x o f t h e s t e r e o c o m p l e x of PMMA Based on X - r a y
c a l c u l a t i o n s , B o s s c h e r e t al. ( r e f . 100) a r r i v e d
at the
140
:C~c~ic l-Helix)
~Isotqctic
IC
le} F i g . 22. S c h e m a t i c r e p r e s e n t a t i o n of the chain ordering in the crystalline s t e r e o c o m p l e x o f PMMA: (a} m o d e l p r o p o s e d b y L i q u o r i e t al. ( r e f . 33}; (b} d o u b l e h e l i c a l m o d e l p r o p o s e d b y B o s s c h e r e t al. ( r e f . 100). T h e f i g u r e i s t a k e n f r o m r e f . 63.
conclusion
that
the stereocomplex
which an i-chain
consists
s-chain
with a 60/4 helical conformation
parallel
straight
agreement
chains
of i- and
with the structure
The self-aggregates with the stereocomplex Also, here
near
assumed forming
that
I01), based
has been
obtained
(together pairs
studies
12}; 2) t h e d e c r e a s e
the reaction
aggregation
s-sequences
than
of double
occurs
Quite recently,
of the aggregated
some minimum length
by interaction
with near-to-extended
further
mutual (cf. P a r t
V-B and
and
is the presence
of Pig.
with
the order
( r e f . 129} f a v o r s
chain conformation
interaction
formation
giving
of two chains;
fraction
stereoregularity
of s-PMMA self-aggregate
of s-PMMA self-aggregates
are paired,
e t al. ( r e f .
helices in s-PMMA aggregates
for s-PMMA of various
formation
it m a y b e
by Kusuyama
s-PMMA.
with a
segmental
of s-PMMA the chains
is admitted
of s-PMMA in the solution
of s-PMMA aggregate
for the generation
a long distance,
p = 0 f o r at-PMMA} i n d i c a t e
in the rate
concentration
in the solid state.
Based on this analogy,
( r e f . 111): 1) t h e v a l u e s
longer
of similar features
and
are parallel over
of crystalline
b y NMR s p e c t r o s c o p y
of s-sequences
The model assuming
chain form and with a retarded
structures
the existence
with the fact that
decreasing
where
sequences
(ref. 22,54,110).
on X-ray
supporting
by an
helix.
in solution
helix; this possibility
evidence
determined
of the double
also in the ordered
a double
(Fig. 22b).
of s-PMMA exhibit a number
to the extended
mobility in solution
helix in
is surrounded
s - P M M A ( r e f . 21} i s l i k e w i s e i n p r i n c i p l e
o f PMMA, b o t h
the interacting
conformation
of a double-stranded
with a 30/4 helical conformation
n = 2 of
a double
helix
3) a p r e r e q u i s i t e of long
in solutions.
Such
141 sequences
already
indicate
that
solutions
represent
the content
opinions
on the existence
( r e f . 24,101) s u p p o s e the existence solvent
sequences
solvent
studies
have
shown
that
condition
According
to t h e l a t t e r
for the formation conformational interaction
of the crystalline
structure
presence
structure
of s-PMMA chains
of long s-sequences
and
practically
thus
for the
structure On the
no residual
of solvent
of the crystalline
the solvent
e t al.
that
complexes with s-PMMA.
the simultaneous
references,
assume
of the crystalline
thin films containing
for the existence
Kusuyama
molecules is essential
of s-PMMA; they
inclusion
the effect of
in s-PMMA.
in the stabilization
crystalline
in ( r e f . 22).
in acetonitrile.
concerning
of solvent
structure
different
o-dichlorobenzene
not formed
structure
of very
necessary
are
of crystalline
directly
isomorphous
hand,
and
published
the presence
h e l i x ; IR r e s u l t s
is not very
toluene
been
that
have
of the crystalline
participates
forming
(nuclei) of a single
s-PMMA self-aggregates
Quite different
other
of these
of s-PMMA in acetonitrile,
In spite of that,
solvent
sections
is not a
form (ref. 22,38,102).
is a necessary
condition
o f s - P M M A ; it a f f e c t s
and
promotes
the stable
makes
possible
subsequent
only
the mutual
crystallization. This analysis
indicates
that
while s-PMMA and
one hand
and
i-PMMA o n t h e o t h e r
behavior
( r e f . 95,97), t h e s t r u c t u r e
i-PMMA, s - P M M A a n d it i s p r o b a b l y units
per
hand
by double
the stereocomplex very
of the crystalline
stereocomplex
formed
exhibit
PMMA (cf. P a r t
different phase
PMMA
is very
similar in
I I I - B ) ; i n all t h r e e
helices with a large
number
cases,
of monomer
turn.
VIII. OTHER AGGREGATES OF PMMA A. I n t e r a c t i o n s
of stereoregular
PMMA w i t h MMA m o n o m e r o r w i t h d i m e r
m o d e l o f PMMA Interactions
in the ternary
systems
PMMA-d8)/solvent
( r e f . 105) a n d
PMMA-d8)/eolvent
(ref.
MMA/(i- or s- or stereocomplex
DMTMGA/(i- or s- or stereocomplex
108) w e r e
studied
b y 1H NMR s p e c t r o s c o p y .
M/~
DMTMGA
HA ~.
/ CH3 C
/ HB
=
C
~H 3 CH 3
\
-
C
i H3 -
i COOCH 3
COOCH 3
CH 2
-
on
crystallization
- CH 3
I COOCH 3
142 The temperature NMR s p e c t r a
dependence
of solutions
interaction
of t h e c h e m i c a l s h i f t o f HA p r o t o n s
o f MMA i n v a r i o u s
o f MMA m o l e c u l e s w i t h DMF.
PMMA a c t s a s a f u r t h e r
component
solvents
revealed
In the system
interacting
Studies
of integrated
cases
a part
P M M A - d 8.
band
intensities
containing
This interaction
{10-15%} o f t h e DMTMGA m o l e c u l e s
In this interaction,
DMTMGA b e h a v e s
s-PMMA in interactions stereocomplex
{ r e f . 108).
arrangement
DMTMGA a n d aggregates These
in s-sequences
results
even
very
s-configuration contact
chain about
o f PMMA s t e r e o c o m p l e x
are in direct
relation
in the presence
short
oligomers
may be capable
chain
stable
The fact
( d i m e r s , t r i m e r s ~ etc.} i n
{on t h e NMR t i m e s c a l e }
with a certain
{ r e f . 105) f a v o r s
arrangement
the growth
o f MMA
of the nascent
tendency
o f MMA o f i-PMMA a n d
is active
the basis
of the so called replica
o f MMA p e r f o r m e d
also in the course
effect
studied
and in anionic
is identical
in the stereocomplex helix model.
of papers,
of stereoregular the structure
of i- and
supports
the double
o f i-PMMA p r o c e e d s
obtained
with an s-PMMA matrix are less unequivocal.
o f MMA i n t o l u e n e
systems;
the
PMMA h a s a l s o b e e n by
of the stereocomplex
While polymerization
the s-PMMA matrix on the stereoregularity
of
o f PMMA f o r m e d
are parallel over
definitely
is
both in radical
s-PMMA proves
presence
polymerization
and
polymerization
b y O r l o v a e t al. { r e f . 64),
with the structure
by the mixing of solutions s-chains
study
(ref. 49,62,113,138-140)
The observation'that
polymerization
process
o f MMA, w h e r e
in a number
o f MMA i n s o l i d m a t r i c e s
{ r e f . 141).
to s t e r e o c o m p l e x
o f i-PMMA l e a d s t o t h e f o r m a t i o n
Since the original
has been
(ref. 34,35,64,67,131-137} polymerization
s-PMMA chains
of the polymerization
polymerization
in the presence
s-PMMA and vice versa. the replica
polymerication
t h e i-PMMA m a t r i x .
The strong
i- and
of
or s-PMMA self-
o f i-PMMA ( s e e n e x t s e c t i o n ) .
of close and
formation
prepared
conformer
to t h e s o c a l l e d r e p l i c a
of the growing
t h e PMMA c h a i n s
B. R e p l i c a p o l y m e r i z a t i o n
replica
by the similarity of the
in the most favored
w i t h i-PMMA ( r e f . 108}, t o g e t h e r
molecules about
studied
can also replace
a n a n a l o g o f t h e PMMA
is explained
groups
in some
with
( s e e F i g . 19).
o f MMA p e r f o r m e d that
The behavior of ester
that
interact
s i m i l a r to s - P M M A {i.e.,
of s-PMMA and
w i t h i-PMMA, f o r m i n g
1H NMR s p e c t r a
shown
strongly
is
o f PMMA.
resolution
i- or s-PMMA-d 8 have
DMTMGA c a n l i n k u p i n s e l f - a g g r e g a t e s
geometrical
in high
1H
MMA/PMMA-d8/DMF,
w i t h MMA.
the same with i-PMMA-d8, s-PMMA-d 8 or the stereocomplex
o f DMTMGA i n s o l u t i o n s
in t h e
specific
by the replica
that
the
and
o f MMA i n t h e mechanism,
data
The negative
of the polymer
( r e f . 34,35,49,113,140}
again
long distances
generated
was explained
effect of by by
143 s e l f - a g g r e g a t i o n of s-PMMA; p r o b a b l y t h e g r o w t h of t h e p o l y m e r c h a i n c a n n o t p r o c e e d via r e p l i c a p o l y m e r i z a t i o n if a l m o s t all t h e s-PMMA matrix is p r e s e n t in t h e a g g r e g a t e d form in t h e p o l y m e r i z a t i o n s y s t e m (ref. 109).
C o n t r a r y to
t h e s t u d i e s b y Challa e t al. ( r e f . 34,35,132,133), in a r e c e n t p a p e r M a t s u z a k i e t al. ( r e f . 142) did n o t d e t e c t a n y e f f e c t of t h e s-PMMA matrix on t h e s t e r e o r e g u l a r i t y of t h e f o r m e d p o l y m e r d u r i n g p o l y m e r i z a t i o n in DMF a n d a c e t o n i t r i l e (i.e., in media w h e r e p r o n o u n c e d s e l f - a g g r e g a t i o n of s-PMMA d o e s n o t t a k e place).
F u r t h e r i n f o r m a t i o n on t h e r e p l i c a p o l y m e r i z a t i o n of MMA
c a n be o b t a i n e d from two r e v i e w a r t i c l e s ( r e f . 143,144}.
C. O t h e r s y s t e m s In t h i s s e c t i o n , we s h o u l d like to b r i e f l y m e n t i o n p a p e r s d e s c r i b i n g s t e r e o s p e c i f i c i n t e r a c t i o n s o f similar t y p e a s t h o s e of s t e r e o r e g u l a r PMMA, o b s e r v e d with o t h e r p o l y m e r s .
Challa e t al. ( r e f . 36,94,100,145,146) h a v e
s t u d i e d in d e t a i l i n t e r a c t i o n s in m i x t u r e s of s t e r e o r e g u l a r PMMA with s t e r e o r e g u l a r f o r m s of PMAA, b o t h in s o l u t i o n a n d in t h e solid s t a t e .
Of t h e
f o u r p o s s i b l e c o m b i n a t i o n s of s t e r e o r e g u l a r PMMA a n d PMAA, s t a b l e s t e r e o a s s o c i a t i o n t a k e s p l a c e o n l y in o n e c a s e (i.e.., b e t w e e n i-PMMA a n d s-PMAA).
The complex i-PMMA/s-PMAA, a l t h o u g h it is w e a k e r , r e s e m b l e s t h e
s t e r e o c o m p l e x of PMMA a n d a c c o r d i n g to X - r a y d i f f r a c t i o n , it h a s a p r a c t i c a l l y identical structure
( r e f . 94,100).
A n o t h e r a n a l o g of t h e s t e r e o c o m p l e x of PMMA h a s b e e n o b s e r v e d in m i x t u r e s of o p t i c a l l y a c t i v e e n a n t i o m e r s ; namely, i s o t a c t i c p o l y ( m e t h y l b e n z y l m e t h a c r y l a t e ) ( r e f . 147) a n d i s o t a c t i c p l y ( ~ - m e t h y l - ~ - e t h y l - ~ - p r o p i o l a c t o n e ) (ref. 148}.
The m e l t i n g p o i n t s o f t h e s e s t e r e o c o m p l e x e s in t h e solid s t a t e a r e
230"C a n d 202"C, r e s p e c t i v e l y ; in t h e s e c o n d c a s e , t h e m e l t i n g p o i n t o f t h e complex is h i g h e r b y a b o u t 40"C t h a n t h e m e l t i n g p o i n t s of t h e c o m p o n e n t s . Some e v i d e n c e also e x i s t s f o r t h e p r e s e n c e of a s t e r e o c o m p l e x c o m p o s e d of a c o m b i n a t i o n of i s o t a c t i e a n d s y n d i o t a c t i c p o l y ( m e t h y l ~ - c h l o r o - a c r y l a t e ) (ref. 149).
V i s c o e l a s t i c b e h a v i o r i n d i c a t e s t h e p r e s e n c e of s t r o n g i n t e r m o l e c u l a r
i n t e r a c t i o n s in t h e i - p o l y ( e t h y l m e t h a c r y l a t e ) w h i c h may be d u e to i - s e q u e n c e s ( r e f . 150).
I n t e r a c t i o n s of t a c t i c s e q u e n c e s a r e a l s o s u p p o s e d to
e x p l a i n t h e a g g r e g a t i o n b e h a v i o r o b s e r v e d w i t h s o l u t i o n s of p o l y m e t h a c r y l a t e s with m e s o g e n i c s i d e g r o u p s of t h e b e n z o i c acid p h e n y l e s t e r t y p e (ref. 151,152,153). IX.
CONCLUSIONS Long stereoregular sequences of PMMA have a strong tendency to mutual
interactions. B o t h the sequences of equal stereoregularity (i-i or e-s) and
s e q u e n c e s of d i f f e r i n g s t e r e o r e g u l a r i t y interaction.
(i-s) are capable of mutual
C o n s e q u e n t l y , t h e a g g r e g a t e s of s t e r e o r e g u l a r PMMA c a n be
144 d i v i d e d i n t o t h r e e t y p e s : 1) s e l f - a g g r e g a t e s
of i-PMMA; 2) s e l f - a g g r e g a t e s
of
s-PMMA; a n d 3) t h e s o c a l l e d s t e r e o c o m p l e x of PMMA f o r m e d b y t h e m i x i n g of s o l u t i o n s of i - a n d s-PMMA.
T h e s e t h r e e t y p e s of a g g r e g a t e s
t h e r m a l s t a b i l i t y a n d b y t h e e x t e n t of a g g r e g a t i o n self-aggregates
The
of i-PMMA e x h i b i t t h e h i g h e s t t h e r m a l s t a b i l i t y a n d t h e
self-aggregatres aggregates
differ by their
in t h e g i v e n s o l v e n t .
of s-PMMA e x h i b i t t h e l o w e s t t h e r m a l s t a b l i t y , w i t h t h e
of t h e s t e r e o c o m p l e x s o m e w h e r e i n b e t w e e n .
a t t e n t i o n h a s b e e n p a i d to t h e a g g r e g a t e s a l s o to t h e s e l f - a g g r e g a t e s
of s-PMMA.
The greatest
of t h e s t e r e o c o m p l e x a n d r e c e n t l y
Information about the self-aggregates
of i-PMMA i s s c a r c e d u e to t h e f a c t t h a t t h e c o n t e n t of t h e s e a g g r e g a t e s a l w a y s r e l a t i v e l y low, i r r e s p e c t i v e that the self-aggregates
close
of c r y s t a l l i n e i-PMMA m i g h t i n d i c a t e t h a t t h e
of i - P M M A i n s o l u t i o n a r e s m a l l c r y s t a l l i t e s .
The self-aggregates
of s-PMMA a n d t h e s t e r e o c o m p l e x of PMMA e x h i b i t a
n u m b e r of c o m m o n f e a t u r e s .
I n b o t h c a s e s , a g g r e g a t i o n is a v e r y c o m p l e x
p r o c e s s d e p e n d i n g on m a n y f a c t o r s . e f f e c t of time.
The observation
of i-PMMA a r e d e c o m p o s e d o n l y a t t e m p e r a t u r e s
to t h e m e l t i n g t e m p e r a t u r e self-aggregates
of t h e t y p e of s o l v e n t .
is
Of g r e a t i m p o r t a n c e i s , f o r e x a m p l e , t h e
T h e f o r m a t i o n of t h e " p r i m a r y " a g g r e g a t e s ,
r a p i d and which is p r o b a b l y p r e c e d e d conformational structure
w h i c h is r e l a t i v e l y
b y a n e v e n m o r e r a p i d c h a n g e of
of t h e s t e r e o r e g u l a r
s e q u e n c e s , i s followed b y t h e
v e r y slow p r o c e s s of t h e s o c a l l e d s e c o n d a r y a g g r e g a t i o n , w i t h s t e a d i l y i n c r e a s i n g particle size.
This p r o c e s s is d e t e c t e d with d i f f e r e n t s e n s i t i v i t y
by various physical methods. One of t h e d e c i s i v e f a c t o r s i n t h e s e l f - a g g r e g a t i o n s t e r e o c o m p l e x formation is the s t e r e o r e g u l a r i t y ordered
structure
interacting
of s-PMMA a n d i n
of p o l y m e r c h a i n s .
A stable
i s f o r m e d o n l y in t h o s e c a s e s w h e r e t h e l e n g t h of t h e
s e q u e n c e s is l o n g e r t h a n some minimum l e n g t h .
The actual values
o f t h i s m i n i m u m l e n g t h d e p e n d o n t h e s o l v e n t ; i n t h e c a s e of t h e s t e r e o c o m p l e x of PMMA, it w a s p o s s i b l e to c l a s s i f y t h e s o l v e n t s a s s t r o n g l y c o m p l e x i n g ( m i n i m u m l e n g t h of a s s o c i a t e d s - s e q u e n c e s a n d w e a k l y c o m p l e x i n g (q = 10 m o n o m e r u n i t s } . seif-aggregates
q : 3-4 m o n o m e r u n i t s }
I n t h e c a s e of
of s-PMMA, t h e e x p e r i m e n t a l l y f o u n d m i n i m u m l e n g t h q i s
e q u a l to 9 m o n o m e r u n i t s .
Also, t h e t h e r m a l s t a b i l i t y of t h e a g g r e g a t e s
determined by stereoregularity; formed by long stereoregular by short sequences.
the temperature
is
of " m e l t i n g " of a g g r e g a t e s
sequences is higher than for aggregates
The solvent has a less pronounced
formed
effect on the
t h e r m a l s t a b i l i t y of t h e a g g r e g a t e s . I n b o t h c a s e s ( s t e r e o c o m p l e x a n d s-PMMA s e l f - a g g r e g a t e s ) ,
t h e r a t e of
a g g r e g a t i o n i n c r e a s e s w i t h t h e i n c r e a s i n g c o n c e n t r a t i o n of t h e s o l u t i o n a n d it increases very rapidly with the decreasing temperature r o l e of s o l v e n t i n t h e a g g r e g a t i o n
of a g g r e g a t i o n .
p r o c e s s i s n o t q u i t e c l e a r so f a r .
The
145 Aggregation non-polar
of stereoregular solvents
the complexing such
PMMA t a k e s
even
which can strongly It is interesting
self-aggregation
For stereoregular
interact
basis
related
conformation
sequences turn. than
very
studies
near
sequences
of the i-chain,
stereocomplex
leading
i/s = I/1.5
to I / 2 .
The formation
by the much lower segmental in solution
the stereoregularity represent systems chains
of the components
where
the degree
participate
After removal of the solvent self-aggregates generated
aggregation
the morphological
turn;
crystalline
the chains
even
is very
the
in the solid state.
crystalline.
Thus,
Solid
the structure
of stereoregular
PMMA
As also for crystalline helix with a large
it may be stated
forms of stereoregular
In
o f PMMA e x i s t , t h e s t r u c t u r e
form a double
therefore,
helices can
formed.
or gels where
process.
that
the double
on
(p ~ 85%), a l m o s t a l l PMMA
properties
per
structure)
to
helices.
and
i-PMMA, it w a s f o u n d
Structures
is preserved
of the
helices is also
motion in the
network
by means of the aggregation
of monomer units
stereocomplex)
is large
from solutions
in this way is partially
can be affected
all three
on solvent,
of double
per
o f PMMA, i n d e p e n d e n c e
of s-PMMA or the stereocomplex
during
PMMA p r e p a r e d (including
and
of
helix is larger
stoichiometry
as compared
of the physical
of aggregation
in the formation
of the s-chain
2 orders
a
stereoregular
of the double
In the stereocomplex
points
The results
mobility; segmental
is slower by about
only the crosslink
o f PMMA a s s u m e
of monomer units
with the found
aggregates
segments.
structure.
o f PMMA, t h e r a d i u s
in agreement
The mobility
Both in the
the chains
number
of
role in the
to a g g r e g a t i o n .
the interacting
helix, with a large
manifested
non-associated
that
with some other
hindered.
chain
in both cases
In the stereocomplex
is so strong even
o f MMA.
with the stereocomplex
in the stereocomplex,
that
is not parallel.
the polymerization
play an important
is strongly
to the extended
indicate
form a double
that
groups
in the aggregates
of s-PMMA and
(e.g.,
on the
polymerization
to interaction
of s-PMMA and
the ester
of stereoregular
groups
aggregates
recent
that
formation
are formed
group
of solvent
in
polymers.
Both with the self-aggregates
interactions
the effect
of the so called replica
stereoregular
with
has not been observed
o f PMMA d u r i n g
PMMA, t h e t e n d e n c y
in
has no connection
with the carbonyl
to note that
s i m i l a r to t h e s t e r e o c o m p l e x
PMMA, it w a s f o u n d
of ester
Aggregation
of the stereocomplex
is the physical
chemically
parameter
of s-PMMA and on stereocomplex
The formation
aggregates
place both in polar and
the solubility
ability of the solvent.
solvents
chloroform).
process
and
that
number
the structure
of
PMMA (i-PMMA, s - P M M A ,
similar.
of the double
biological macromolecules.
helix type Stereoregular
so far
have
only been
PMMA's a r e t h e f i r s t
considered synthetic
with
146 polymers where double helices generated by physical interactions have been observed.
So f a r , t h i s s t r u c t u r a l a n a l o g y h a s n o t b e e n e x p l o i t e d in t h e
a p p l i c a t i o n s of s t e r e o r e g u l a r PMMA.
X.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
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*References marked with an asterisk appeared very recently when the text was a l r e a d y c o m p l e t e ; t h e y a r e c i t e d in Table 1 only. ACKNOWLEDGEMENT The
authors
reproduce
acknowledge
the figures
the
p e r m i s s i o n of t h e
from t h e f o r m e r p a p e r s :
following p u b l i s h e r s
1) B u t t e r w o r t h
to
& Co., L t d . ,
G u i l d f o r d (Figs. 2,4); 2} Hitthig & Wepf V e r l a g , Basel (Figs. 6,7,10,11,13,14); 3} S p r i n g e r (Figs. 20,22).
V e r l a g , H e i d e l b e r g (Fig. 19); a n d 4} S t e i n k o p f f V e r l a g , D a r m s t a d t