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The effect of orientation on the rotational and translational diffusion of a spin probe in polypropylene
0032-3950/79]0801-1851$07.50~fb
Polymer Science U.S.S.R. Vol. 21, pp. 1851-1857. © Pergamon Press Ltd. 1980. Printed in Poland
THE EFFECT OF ORIENTATION ON THE ROTATIONAL AND TRANSLATIONAL DIFFUSION OF A SPIN PROBE IN POLYPROPYLENE* I.
I.
BARASHKOVA,
A.
M.
VASSERMAI~" a n d
N.
YA.
RAPOPORT
I n s t i t u t e of C h e m i c a l P h y s i c s , U . S . S . R . A c a d e m y of Sciences
(Received 12 April 1978) T h e r o t a t i o n a l a n d t r a n s l a t i o n a l diffusion of a spin p r o b e in isotropic a n d orient a t e d p o l y p r o p y l e n e is i n v e s t i g a t e d . I t is s h o w n t h a t w h e n a free r a d i c a l p r o b e is introduced into the polymer after it has been stretched, the main factors affecting its t r a n s l a t i o n a l diffusion a r e g e o m e t r i c a l h i n d r a n c e s w h i c h increase i n t h e course o f o r i e n t a t i o n . O n t h e o t h e r h a n d ; w h e n t h e r a d i c a l is i n t r o d u c e d before s t r e t c h i n g , b o t h g e o m e t r i c h i n d r a n c e s a n d t h e m o b i l i t y o f a m o r p h o u s regions i n w h i c h i t finds i t s e l f o n r e c r y s t a l l i z a t i o n e x e r t a n effect.
THE effect of crystallinity on the rotational and translational diffusion of a spin probe in polypropylene was discussed in [1]. It was shown that segmental mobility is the main factor affecting the diffusional processes in an isotropie, crystalline polymer. In the present paper the effect of orientation on the rotational a n d translational diffusion of a spin probe is studied, for the purpose of discovering the mechanism of the diffusional processes taking place in orientated polymers. Moplen, i s o t a c t i c P P w i t h M = 60,000 w a s used. F i l m s of t h e p o l y m e r were m o u l d e d a t 190% u n d e r a p r e s s u r e of 250 k g / c m ~ for 3 m i n . T h e y were t h e n cooled r a p i d l y t o 1 4 - 1 6 ° i n cold w a t e r , w h e r e b y a fine s p h e r u l i t i c s t r u c t u r e w a s p r o d u c e d [2]. T h e m a t e r i a l o b t a i n e d in t h i s w a y c a n b e o r i e n t a t e d easily, t o a h i g h d e g r e e o f e x t e n s i o n . O r i e n t a t i o n w a s c a r r i e d o u t a t 130°C a n d t h e d r a w r a t i o 2 w a s v a r i e d b e t w e e n 1 a n d 10, b e c a u s e a t h i g h e r d r a w r a t i o s microfissures c a n arise in t h e p o l y m e r a n d t h e s e e x e r t a s u b s t a n t i a l effect o n t h e diffusional processes. T h e film t h i c k n e s s l w a s 4 0 - 8 5 ~. T h e s p i n p r o b e t h a t w a s u s e d w a s the stable nitroxyl radical 2,2,6,6-tetramethylpiperidin-l-oxyl, which was introduced into t h e i s o t r o p i c or p r e v i o u s l y o r i e n t a t e d film f r o m t h e v a p o u r phase. I n b o t h cases t h e films were h e a t e d a t 5 0 - 6 0 ° for 2 h r in o r d e r to d i s t r i b u t e t h e r a d i c a l u n i f o r m l y i n t h e film. T h e c o n c e n t r a t i o n o f t h e r a d i c a l in t h e p o l y m e r w a s n o t m o r e t h a n a b o u t 5 × 10 ~7 s p i n s / e r a a. T h e c o r r e l a t i o n t i m e s rc a n d t h e coefficients of r o t a t i o n a l diffusion, Dr:(6v¢) -1, were det e r m i n e d f r o m t h e E P R s p e c t r a as in [3]. T h e coefficients of t r a n s l a t i o n a l diffusion (D~ pp) were d e t e r m i n e d f r o m t h e r a t e of d e s o r p t i o n of t h e r a d i c a l f r o m t h e film, i n t h e f o l l o w i n g way. S a m p l e s of t h e p o l y m e r c o n t a i n i n g t h e r a d i c a l were p l a c e d i n t h e r e s o n a t o r of t h e E P t ~ s p e c t r o m e t e r , t h e n a c u r r e n t o f air w a s b l o w n t h r o u g h . T h e k i n e t i c s o f d e s o r p t i o n w e r e followed b y t h e c h a n g e i n c o n c e n t r a t i o n of t h e free r a d i c a l i n t h e p o l y m e r film. T h e coeffic i e n t s of diffusion D~ pp were c a l c u l a t e d f r o m t h e i n i t i a l sections (qt/q~<0.5) o f t h e d e s o r p •
* V y s o k o m o l . soyed. A21: No. 8, 1683-1687, 1979. 1851
I. I. B ~ s ~ x o v A
18~ii
e~ . L
~on curves by means of the equation
q~o
T. = . , t - - ~ l
'
(')
where q = and q, are the equilibrium quantity of the radical and its quantity desorbed after time t, and 10 and I are the intensities of the F,PR signal initially and at time t. When ql/q®>0-5 desorption of the radical is described by the equation
±,-z ql/q®=
Io
l-(X//o) o~1- b
"kOv" ,
~ I O " % ,
( lI
(2)
]
to~
~
I
J',~
30
-0.0
5
-06
7
.~
",.
1
I
%./000
a
8
= 1-- - ~ e x p
- ~ e ,
I
i~
zooo
8eC
--%,_ I
500
I
I
1
1500
1".o
I
2500 T i m e 7sSC
FIG. 1
F~G. 2
FIG. 1. Kinetic curve of desorption of the radical (a) (PP, 1=4.5, radical added before° si~etching, l = 8 5 p , 80°) and corresponding curves using the coordinates of equation (1) (b), and 2 (c). Fie. 2. E P R spectra of the probe radical in orientated PP (i----7, radical added before stretching): 1--100% 2--85 °, 3--66 °, 4--26 °, 5 - - - - 6 °, 6 - - - - 4 7 °, 7 - - - - 7 0 °, 8 - - - - 9 5 °, 9-- -- 120°, 1 0 - 196 °. -
-
A n e x a m p l e of a kinetic curve of desorption of t h e radical a n d modified f o r m s o f t h e curve, using t h e coordinates o f equations (1) a n d (2), are p r e s e n t e d in Fig.' 1. I t has been shown previously [1, 3] t h a t equations (1) a n d (2) describe t h e kinetics of diffusion of a free radical p r o b e in isotropic polymers. F r o m t h e results p r e s e n t e d in Fig. 1 it is seen t h a t these equations describe diffusion o f t h e radical in o r i e n t a t e d specimens also. T h e coefficients of diffusion calculated f r o m different p a r t s of t h e diffusion curve are in satisfactory agreement. F o r e x a m p l e , for a p o l y m e r o r i e n t a t e d to I = 7 (l----40/l), into which the radical w a s
Rotational and translational diffusion of spin probe in polypropylene
1853
introduced before orientation, the values of D~pp at 85 °, calculated from equations (1) and (2) are 1.8× 10 -9 anc[ 1.6× 10 -9 craB/see respectively. For a ssmp]o with 4----4.5 (/-=85 p), when the radical is added before the film is stretched, the values of D~pp at 80 °, calculated by equations (1) and (2) are 3.1 × 10 -9 cm2/sec. I n future we shall use only equation (1) for determination of D~pp. The dependence of D~pp on film thickness was also investigated and it was found t h a t when lies between 40 and 85/z the coefficients of rotational and translational diffusion of the radical are independent of film thickness. The details of the method for determining the coefficients of translational diffusion of stable radicals in polymers by the E P R method, are given in [3]. 80 q
I
20 -I0 -40 I
I
I
T'-TC
I
I
2
=t 2 10-Io 2.5 FzG. 3.
Z I ~ II11
a.s
I
~5 /Of7;'K
Temperature dependence of vc of the radical in specimens 7 (2): radical added before stretching
a t ~t~- 1
(1) and
I t must be emphasized t h a t the coefficients of translational diffusion in isotropic and orientated, crystalline polymers, determined from the kinetics of desorption (or sorption) of ]ow-molecnlar particles, are apparent quantities. This is because a crystalline polymer is a diffusion medium in which diffusion is hampered by purely geometrical hindrances, because of the presence of crystallites, which are impervious to the diffusing particles [4]. I n the course of its motion the particle must be deflected around the crystallites and consequently the effective path of diffusional transfer is increased. In terms of equations (1) and (2), this is equivalent to an apparent increase in film thickness. In order to take account of this the apparent coefficients of diffusion in a crystalline polymer are related to the diffusion coefficient in amorphous regions Dam by the simple relationship D~PP----Dam/~, (3) where ~ is a coefficient allowing for the increased length of the transport path resulting from the geometrical hindrances. The rotational diffusion of a spin probe is dependent on the mobility of the sections of macromolecules surrounding the rwlical, whereas the translational
1854
l . I . BAP.AS~KOVAe¢ al.
.
diffusion, according to equations (1) and (2), is affected both by segmental mobility in the amorphous regi6ns and by geometrical hindrances to diffusion. Let us now consider results obtained in investigation of the "rotational diffusion of the spin probe. Examples.of EPR spectra at different temperatures are shown in Fig. 2. Figure 3 shows the temperature dependence of the correlation
90
Dp,se~ I 2
8O I
I
l
l
i0-o 8!
I
llO
98 78 I l l
,
58 T,°C I
I
x
I
fl
F
•3
~..
.4 4
×
o 3 I
I
2"75
I
I
I
I
z.s5 103/T,°K
I
2'F
I
2"8
3
I0
°g
FIG. 4. Temperature dependence of the coefficient of t r a n s l a t i o n a l ( a ) and rotational (b)
diffusion of the radical in PP: 1--isotropic sample; 2 - 4 - - r a d i c a l added before stretching; 2 ' - 4 ' - - a f t e r stretching: 4=4"5 (2, 2'), 7 (3, 3') a n d 10 (4, 4').
time of the probe radical, according to the Arrhenius equation. Above the glass temperature (259°K [6]) the correlation time in an isotropic specimen is lower than in an orientated specimen, when the probe is introduced into the latter before stretching. At lower temperatures the correlation times in orientated and unorientated specimens are more or less the same. Therefore for comparison of the coefficients of rotational and translational diffusion, the high temperature region was investigated in detail (Table and Fig. 4). It is important to note that the values of D~pp and Dr are dependent on the method of introduction of the radical into the specimen. Wher~ the radical is introduced into isotropic specimens, when orientation takes place both the translational and rotational mobility decrease. However the energy of activation for rotational diffusion decreases, while for translational .diffusion it increases, as the degree of stretching is increased. For the radical incorporated in previously orientated specimens, the values of Dr are practically independent of the degree of stretching at 2.=4.5 and 7, whereas the values of D~pp fall in comparison with the isotropie polymer. At 2 = 10 the values of Dt and Et are lower than in the isotropie polymer.
Rotational and translational diffusion of spin probe in polypropylene
1855
According to present views [7, 8], when crystalline polymers are stretched uniaxially recrystallization occurs. As a result of this a spherulitic polymer be. comes fibrillar. In these c i r c u m s t a n c e s o r i e n t a t i o n of the crystallites and of t h e macromoleeules in amorphous regions occurs, the density of the amorphous phase increases and the intensity of molecular motion decreases. The radical, when introduced after orientation, does not enter the thin sections of amorphous material of low mobility, pressed between the fibrils, but becomes distributed in relatively accessible, more mobile regions. In specimens at ~=4.5 and 7 the mobility of the amorphous phase in such regions is much the same as in the amorphous regions of the unorientated polymer. This explains why Dr of the radical introduced into an orientated specimen is independent of the degree of stretching. At high degrees of orientation (,~= 10) the segmental mobility even of such ac, cessible regions is lower t h a n in the isotropic polymer. A C T I V A T I O N E N E R G I E S A N D P R E - E X P O N E N T I A L FACTORS
(Do) F O R
ROTATIONAL AND TRANSLA-
T I O N A L D I F F U S I O N OF A S P I N P R O B E I N I S O T R O P I C AI'ffD O R I E N T A T E D
Draw
ratio A
Isotropic sample 4.5 7.0 10.0 4.5 7.0 10.0
Method of adding probe m
Before stretching After stretching
Dr
Dt D0,
cm~•sec-~
PP
Et,
Do
kcal/mole
see-1
Er
kcal/mole
5 X 10 5
22"5
4× 1016
12"4
1"3 X
107 5 X 101°
25"5 32"0
4"5 X 10I~ 1 × 1015 9"4× 1013
11"0 10"2 8"6
3-2 X 10~ 2"0 × 105
22"5 22"5
4 X 10TM 4 X 1018 9"9 × 10~3
12"4 12'4 8"6
The translational motion of the probe when introduced into orientated specimens, takes place along amorphous regions, the mobility of which at A~<7 is virtually the same as the mobility of amorphous regions in an isotropic specimen. The difference between the apparent coefficients of translational diffusion of the probe in the isotropic and orientated polymer is caused only by the geometrical hindrances, which increase when the polymer is orientated. I f it is assumed t h a t y = 1 in the isotropic polymer, the value of ~, characterizing the geometric hindrance arising on orientation, can be calculated from equation (3). At A=4.5 and 7, ~=1.4 ar~d 2.1 respectively, and is independent of temperature. When the spin probe is introduced into isotropic specimens, as a result of recrystallization it is present in the amorphous material of low mobility, completely (or partially) surrounding the fibrils, which are impermeable to the radical. A consequence of the decrease in mobility of amorphous regions in places where the probe is localized, is decrease in its coefficient of rotational diffusion (Fig. 4)..
1856
I . I . B~RASHXOVA e2 a/.
Moreover the amorphous layers between the fibrils can be so thin t h a t the p a s s a g e of t h e probe radical out of them is considerably retarded. These factors explain the reduction in the translational mobility of the probe. Equation (3) can be used for D~pp of a probe introduced before orientation, just as for a probe added after orientation, but it must be borne in mind t h a t in the first instance the mobility of the amorphous phase decrease as the degree of extension is increased. As a result of thermal expansion, the thickness of the amorphous layer between the fibrils increases when the temperature is raised, and this brings about an increase in the number of regions accessible for motion of the probe radical. As a consequence the effective transport path (the coefficient 7) decreases. This explains why at high temperatures the difference between the values of D~pp in orientated and isotropic specimens is less than at low temperatures (Fig. 4, Table). Thus study of the motion of a spin probe enables the contributions to translational diffusion of the mobility of the amorphous phase and of structural factors, to be separated. Orientational drawing of a polymer has a comparatively weak effect, on the rotational mobility of a spin probe, but it exerts a considerable effect on its translational mobility. For a probe radical introduced into the specimen after stretching the decrease in translational diffusion is caused mainly by the increased geometrical hindrance brought about by stretching, whereas when the probe is introduced before stretching its diffusion is affectecl by both geometrical hindrances and the mobility of the amorphous regions in which it is present after recrystallization. It follows from the results of this work, firstly that orientational stretching must displace the boundary between diffusion and kinetic control of chemical reactions, and secondly that the change in molecular dynamics brought about by the structural transformations produced by stretching, must reduce the reactivity and increase the stability of the polymer. The authors are grateful to V. S. Pudov and V. A. Tochin, for discussion of the results of this work. Translated by E. O. PHILLIPS REFERENCES
1. A. M. VASSERMAN and I. I. BARASHKOVA, Vysokomol. soyed. BI9: 820, 1977 (Not translated in Polymer Sci. U.S.S.R.) 2. G. P. ANDRIANOVA, Fiziko-khimiya polyolefinov (The Physical Chemistry of Poly. olefins), p. 154, Izd. "Khimiya", 1974 3. A. M. VASSERMAN, I. I. BARASH]KOVA, L. L. YASINA and V. S. PUD0V, Vysokomol. soyed. AI9: 2083, 1977 (Translated in Polymer Sei. U.S.S.R. 19: 9, 2389, 1977) 4. S. A. REITLINGER, Pro:litsayemost' polimernykh materialov (The Permeability of Polymeric Materials). p. 136, Izd. "Khimiya", 1974
Oxidation of oligoisobutylenes
185~
5. B. I. SAZHIN, ~lektricheskie svoistva polimerov (The Electrical Properties of P o l y m e r s ) , p. 31, Izd. "Khimiya", 1970 6. S. G. K I R Y U S H X I N a n d Yu. A . S H L Y A P N I K O V , D o k l . A k a d . N a u k S S S R 252: 845,
1977 7. F. H. GE1T,, Polimernye monokristally (Polymer Single Crystals). p. 530, Izd. "Khimiya", 1968 (Russian translation) 8. A . P E T E R L I N ,
J. Macromolec.
Sci. B l 1 :
57,
1975
OO32-395Ol79/O8O1-1857507A$010
Polymer Science U.S.S.R. Vol. 21, pp. 1857-1866. O Pergamon Press L~d. 1980. Printed in Poland
O X m A T I O N OF 0LIGOISOBUTYLENES WITH CARBOXYL END GROUPS, AND THE DECARBOXYLATION ASSOCIATED WITH IT* S H . A. ~ASYBULLIN, I. N. ZARIPOV, A. V. DYUL'DEVA a n d I. N. FA[ZUT.T.r~
(Received 26 May 1978) The general relationships found in oxidation of carbon chain polymsrs in solution apply to the oxidation of oligoisobutylene in solution in chlorobenzene. Terminal earboxyl groups in oligoisobutylenes undergo decarboxylation under the action of peroxide radicals and do not affect the total rate of oxidation. The main quantity of C02 is evolved in decomposition of an intermediate product of the moleeular type, formed as a result of uniform attack by peroxide radicals on the methylene groups in the oligomer molecule. The peroxide groups formed in the course of synthesis of the oligoisobutylene, are bound by intramoleeular hydrogen bonds to the carboxyl end groups and consequently are unstable. Their decomposition to free radicals at the beginning of the reaction results in an anomalously high rate of deearboxylation a n d intensification of oxidative degradation of the oligomer. OLIGOISOBUTYLENES ( O I B ' s )
of t h e
CHs
I
O
S
HOOC--CH,--(CH2--C)n--~ CH8
structure CH3
and
I
HO O C - - C H , - - ( C H , - - C ) , - - C H - - C O O H
CH3
OIB -I
I
1
CH, CHa OIB -If
a r e o b t a i n e d b y ozonolysis of i s o b u t y l e n e - d i e n e c o p o l y m e r s [1, 2]. I n c o n t r a s t t o t h e widely used diene c o p o l y m e r s , t h e s a t u r a t e d m a i n c h a i n of O I B ' s s h o u l d i m p a r t high chemical resistance t o these copolymers, w i t h r e s p e c t t o t h e a c t i o n o f h e a t a n d oxygen. On t h e o t h e r h a n d it w o u l d be e x p e c t e d t h a t t h e c a r b o x y l g r o u p s in t h e m a c r o m o l e c u l e , w h i c h u n d e r g o d e c a r b o x y l a t i o n in t h e course o f * Vysokomol. soyed. A21: No. 8, 1688-1696, 1979.
Polymer Science U.S.S.R. Vol. 21, pp. 1851-1857. © Pergamon Press Ltd. 1980. Printed in Poland
THE EFFECT OF ORIENTATION ON THE ROTATIONAL AND TRANSLATIONAL DIFFUSION OF A SPIN PROBE IN POLYPROPYLENE* I.
I.
BARASHKOVA,
A.
M.
VASSERMAI~" a n d
N.
YA.
RAPOPORT
I n s t i t u t e of C h e m i c a l P h y s i c s , U . S . S . R . A c a d e m y of Sciences
(Received 12 April 1978) T h e r o t a t i o n a l a n d t r a n s l a t i o n a l diffusion of a spin p r o b e in isotropic a n d orient a t e d p o l y p r o p y l e n e is i n v e s t i g a t e d . I t is s h o w n t h a t w h e n a free r a d i c a l p r o b e is introduced into the polymer after it has been stretched, the main factors affecting its t r a n s l a t i o n a l diffusion a r e g e o m e t r i c a l h i n d r a n c e s w h i c h increase i n t h e course o f o r i e n t a t i o n . O n t h e o t h e r h a n d ; w h e n t h e r a d i c a l is i n t r o d u c e d before s t r e t c h i n g , b o t h g e o m e t r i c h i n d r a n c e s a n d t h e m o b i l i t y o f a m o r p h o u s regions i n w h i c h i t finds i t s e l f o n r e c r y s t a l l i z a t i o n e x e r t a n effect.
THE effect of crystallinity on the rotational and translational diffusion of a spin probe in polypropylene was discussed in [1]. It was shown that segmental mobility is the main factor affecting the diffusional processes in an isotropie, crystalline polymer. In the present paper the effect of orientation on the rotational a n d translational diffusion of a spin probe is studied, for the purpose of discovering the mechanism of the diffusional processes taking place in orientated polymers. Moplen, i s o t a c t i c P P w i t h M = 60,000 w a s used. F i l m s of t h e p o l y m e r were m o u l d e d a t 190% u n d e r a p r e s s u r e of 250 k g / c m ~ for 3 m i n . T h e y were t h e n cooled r a p i d l y t o 1 4 - 1 6 ° i n cold w a t e r , w h e r e b y a fine s p h e r u l i t i c s t r u c t u r e w a s p r o d u c e d [2]. T h e m a t e r i a l o b t a i n e d in t h i s w a y c a n b e o r i e n t a t e d easily, t o a h i g h d e g r e e o f e x t e n s i o n . O r i e n t a t i o n w a s c a r r i e d o u t a t 130°C a n d t h e d r a w r a t i o 2 w a s v a r i e d b e t w e e n 1 a n d 10, b e c a u s e a t h i g h e r d r a w r a t i o s microfissures c a n arise in t h e p o l y m e r a n d t h e s e e x e r t a s u b s t a n t i a l effect o n t h e diffusional processes. T h e film t h i c k n e s s l w a s 4 0 - 8 5 ~. T h e s p i n p r o b e t h a t w a s u s e d w a s the stable nitroxyl radical 2,2,6,6-tetramethylpiperidin-l-oxyl, which was introduced into t h e i s o t r o p i c or p r e v i o u s l y o r i e n t a t e d film f r o m t h e v a p o u r phase. I n b o t h cases t h e films were h e a t e d a t 5 0 - 6 0 ° for 2 h r in o r d e r to d i s t r i b u t e t h e r a d i c a l u n i f o r m l y i n t h e film. T h e c o n c e n t r a t i o n o f t h e r a d i c a l in t h e p o l y m e r w a s n o t m o r e t h a n a b o u t 5 × 10 ~7 s p i n s / e r a a. T h e c o r r e l a t i o n t i m e s rc a n d t h e coefficients of r o t a t i o n a l diffusion, Dr:(6v¢) -1, were det e r m i n e d f r o m t h e E P R s p e c t r a as in [3]. T h e coefficients of t r a n s l a t i o n a l diffusion (D~ pp) were d e t e r m i n e d f r o m t h e r a t e of d e s o r p t i o n of t h e r a d i c a l f r o m t h e film, i n t h e f o l l o w i n g way. S a m p l e s of t h e p o l y m e r c o n t a i n i n g t h e r a d i c a l were p l a c e d i n t h e r e s o n a t o r of t h e E P t ~ s p e c t r o m e t e r , t h e n a c u r r e n t o f air w a s b l o w n t h r o u g h . T h e k i n e t i c s o f d e s o r p t i o n w e r e followed b y t h e c h a n g e i n c o n c e n t r a t i o n of t h e free r a d i c a l i n t h e p o l y m e r film. T h e coeffic i e n t s of diffusion D~ pp were c a l c u l a t e d f r o m t h e i n i t i a l sections (qt/q~<0.5) o f t h e d e s o r p •
* V y s o k o m o l . soyed. A21: No. 8, 1683-1687, 1979. 1851
I. I. B ~ s ~ x o v A
18~ii
e~ . L
~on curves by means of the equation
q~o
T. = . , t - - ~ l
'
(')
where q = and q, are the equilibrium quantity of the radical and its quantity desorbed after time t, and 10 and I are the intensities of the F,PR signal initially and at time t. When ql/q®>0-5 desorption of the radical is described by the equation
±,-z ql/q®=
Io
l-(X//o) o~1- b
"kOv" ,
~ I O " % ,
( lI
(2)
]
to~
~
I
J',~
30
-0.0
5
-06
7
.~
",.
1
I
%./000
a
8
= 1-- - ~ e x p
- ~ e ,
I
i~
zooo
8eC
--%,_ I
500
I
I
1
1500
1".o
I
2500 T i m e 7sSC
FIG. 1
F~G. 2
FIG. 1. Kinetic curve of desorption of the radical (a) (PP, 1=4.5, radical added before° si~etching, l = 8 5 p , 80°) and corresponding curves using the coordinates of equation (1) (b), and 2 (c). Fie. 2. E P R spectra of the probe radical in orientated PP (i----7, radical added before stretching): 1--100% 2--85 °, 3--66 °, 4--26 °, 5 - - - - 6 °, 6 - - - - 4 7 °, 7 - - - - 7 0 °, 8 - - - - 9 5 °, 9-- -- 120°, 1 0 - 196 °. -
-
A n e x a m p l e of a kinetic curve of desorption of t h e radical a n d modified f o r m s o f t h e curve, using t h e coordinates o f equations (1) a n d (2), are p r e s e n t e d in Fig.' 1. I t has been shown previously [1, 3] t h a t equations (1) a n d (2) describe t h e kinetics of diffusion of a free radical p r o b e in isotropic polymers. F r o m t h e results p r e s e n t e d in Fig. 1 it is seen t h a t these equations describe diffusion o f t h e radical in o r i e n t a t e d specimens also. T h e coefficients of diffusion calculated f r o m different p a r t s of t h e diffusion curve are in satisfactory agreement. F o r e x a m p l e , for a p o l y m e r o r i e n t a t e d to I = 7 (l----40/l), into which the radical w a s
Rotational and translational diffusion of spin probe in polypropylene
1853
introduced before orientation, the values of D~pp at 85 °, calculated from equations (1) and (2) are 1.8× 10 -9 anc[ 1.6× 10 -9 craB/see respectively. For a ssmp]o with 4----4.5 (/-=85 p), when the radical is added before the film is stretched, the values of D~pp at 80 °, calculated by equations (1) and (2) are 3.1 × 10 -9 cm2/sec. I n future we shall use only equation (1) for determination of D~pp. The dependence of D~pp on film thickness was also investigated and it was found t h a t when lies between 40 and 85/z the coefficients of rotational and translational diffusion of the radical are independent of film thickness. The details of the method for determining the coefficients of translational diffusion of stable radicals in polymers by the E P R method, are given in [3]. 80 q
I
20 -I0 -40 I
I
I
T'-TC
I
I
2
=t 2 10-Io 2.5 FzG. 3.
Z I ~ II11
a.s
I
~5 /Of7;'K
Temperature dependence of vc of the radical in specimens 7 (2): radical added before stretching
a t ~t~- 1
(1) and
I t must be emphasized t h a t the coefficients of translational diffusion in isotropic and orientated, crystalline polymers, determined from the kinetics of desorption (or sorption) of ]ow-molecnlar particles, are apparent quantities. This is because a crystalline polymer is a diffusion medium in which diffusion is hampered by purely geometrical hindrances, because of the presence of crystallites, which are impervious to the diffusing particles [4]. I n the course of its motion the particle must be deflected around the crystallites and consequently the effective path of diffusional transfer is increased. In terms of equations (1) and (2), this is equivalent to an apparent increase in film thickness. In order to take account of this the apparent coefficients of diffusion in a crystalline polymer are related to the diffusion coefficient in amorphous regions Dam by the simple relationship D~PP----Dam/~, (3) where ~ is a coefficient allowing for the increased length of the transport path resulting from the geometrical hindrances. The rotational diffusion of a spin probe is dependent on the mobility of the sections of macromolecules surrounding the rwlical, whereas the translational
1854
l . I . BAP.AS~KOVAe¢ al.
.
diffusion, according to equations (1) and (2), is affected both by segmental mobility in the amorphous regi6ns and by geometrical hindrances to diffusion. Let us now consider results obtained in investigation of the "rotational diffusion of the spin probe. Examples.of EPR spectra at different temperatures are shown in Fig. 2. Figure 3 shows the temperature dependence of the correlation
90
Dp,se~ I 2
8O I
I
l
l
i0-o 8!
I
llO
98 78 I l l
,
58 T,°C I
I
x
I
fl
F
•3
~..
.4 4
×
o 3 I
I
2"75
I
I
I
I
z.s5 103/T,°K
I
2'F
I
2"8
3
I0
°g
FIG. 4. Temperature dependence of the coefficient of t r a n s l a t i o n a l ( a ) and rotational (b)
diffusion of the radical in PP: 1--isotropic sample; 2 - 4 - - r a d i c a l added before stretching; 2 ' - 4 ' - - a f t e r stretching: 4=4"5 (2, 2'), 7 (3, 3') a n d 10 (4, 4').
time of the probe radical, according to the Arrhenius equation. Above the glass temperature (259°K [6]) the correlation time in an isotropic specimen is lower than in an orientated specimen, when the probe is introduced into the latter before stretching. At lower temperatures the correlation times in orientated and unorientated specimens are more or less the same. Therefore for comparison of the coefficients of rotational and translational diffusion, the high temperature region was investigated in detail (Table and Fig. 4). It is important to note that the values of D~pp and Dr are dependent on the method of introduction of the radical into the specimen. Wher~ the radical is introduced into isotropic specimens, when orientation takes place both the translational and rotational mobility decrease. However the energy of activation for rotational diffusion decreases, while for translational .diffusion it increases, as the degree of stretching is increased. For the radical incorporated in previously orientated specimens, the values of Dr are practically independent of the degree of stretching at 2.=4.5 and 7, whereas the values of D~pp fall in comparison with the isotropie polymer. At 2 = 10 the values of Dt and Et are lower than in the isotropie polymer.
Rotational and translational diffusion of spin probe in polypropylene
1855
According to present views [7, 8], when crystalline polymers are stretched uniaxially recrystallization occurs. As a result of this a spherulitic polymer be. comes fibrillar. In these c i r c u m s t a n c e s o r i e n t a t i o n of the crystallites and of t h e macromoleeules in amorphous regions occurs, the density of the amorphous phase increases and the intensity of molecular motion decreases. The radical, when introduced after orientation, does not enter the thin sections of amorphous material of low mobility, pressed between the fibrils, but becomes distributed in relatively accessible, more mobile regions. In specimens at ~=4.5 and 7 the mobility of the amorphous phase in such regions is much the same as in the amorphous regions of the unorientated polymer. This explains why Dr of the radical introduced into an orientated specimen is independent of the degree of stretching. At high degrees of orientation (,~= 10) the segmental mobility even of such ac, cessible regions is lower t h a n in the isotropic polymer. A C T I V A T I O N E N E R G I E S A N D P R E - E X P O N E N T I A L FACTORS
(Do) F O R
ROTATIONAL AND TRANSLA-
T I O N A L D I F F U S I O N OF A S P I N P R O B E I N I S O T R O P I C AI'ffD O R I E N T A T E D
Draw
ratio A
Isotropic sample 4.5 7.0 10.0 4.5 7.0 10.0
Method of adding probe m
Before stretching After stretching
Dr
Dt D0,
cm~•sec-~
PP
Et,
Do
kcal/mole
see-1
Er
kcal/mole
5 X 10 5
22"5
4× 1016
12"4
1"3 X
107 5 X 101°
25"5 32"0
4"5 X 10I~ 1 × 1015 9"4× 1013
11"0 10"2 8"6
3-2 X 10~ 2"0 × 105
22"5 22"5
4 X 10TM 4 X 1018 9"9 × 10~3
12"4 12'4 8"6
The translational motion of the probe when introduced into orientated specimens, takes place along amorphous regions, the mobility of which at A~<7 is virtually the same as the mobility of amorphous regions in an isotropic specimen. The difference between the apparent coefficients of translational diffusion of the probe in the isotropic and orientated polymer is caused only by the geometrical hindrances, which increase when the polymer is orientated. I f it is assumed t h a t y = 1 in the isotropic polymer, the value of ~, characterizing the geometric hindrance arising on orientation, can be calculated from equation (3). At A=4.5 and 7, ~=1.4 ar~d 2.1 respectively, and is independent of temperature. When the spin probe is introduced into isotropic specimens, as a result of recrystallization it is present in the amorphous material of low mobility, completely (or partially) surrounding the fibrils, which are impermeable to the radical. A consequence of the decrease in mobility of amorphous regions in places where the probe is localized, is decrease in its coefficient of rotational diffusion (Fig. 4)..
1856
I . I . B~RASHXOVA e2 a/.
Moreover the amorphous layers between the fibrils can be so thin t h a t the p a s s a g e of t h e probe radical out of them is considerably retarded. These factors explain the reduction in the translational mobility of the probe. Equation (3) can be used for D~pp of a probe introduced before orientation, just as for a probe added after orientation, but it must be borne in mind t h a t in the first instance the mobility of the amorphous phase decrease as the degree of extension is increased. As a result of thermal expansion, the thickness of the amorphous layer between the fibrils increases when the temperature is raised, and this brings about an increase in the number of regions accessible for motion of the probe radical. As a consequence the effective transport path (the coefficient 7) decreases. This explains why at high temperatures the difference between the values of D~pp in orientated and isotropic specimens is less than at low temperatures (Fig. 4, Table). Thus study of the motion of a spin probe enables the contributions to translational diffusion of the mobility of the amorphous phase and of structural factors, to be separated. Orientational drawing of a polymer has a comparatively weak effect, on the rotational mobility of a spin probe, but it exerts a considerable effect on its translational mobility. For a probe radical introduced into the specimen after stretching the decrease in translational diffusion is caused mainly by the increased geometrical hindrance brought about by stretching, whereas when the probe is introduced before stretching its diffusion is affectecl by both geometrical hindrances and the mobility of the amorphous regions in which it is present after recrystallization. It follows from the results of this work, firstly that orientational stretching must displace the boundary between diffusion and kinetic control of chemical reactions, and secondly that the change in molecular dynamics brought about by the structural transformations produced by stretching, must reduce the reactivity and increase the stability of the polymer. The authors are grateful to V. S. Pudov and V. A. Tochin, for discussion of the results of this work. Translated by E. O. PHILLIPS REFERENCES
1. A. M. VASSERMAN and I. I. BARASHKOVA, Vysokomol. soyed. BI9: 820, 1977 (Not translated in Polymer Sci. U.S.S.R.) 2. G. P. ANDRIANOVA, Fiziko-khimiya polyolefinov (The Physical Chemistry of Poly. olefins), p. 154, Izd. "Khimiya", 1974 3. A. M. VASSERMAN, I. I. BARASH]KOVA, L. L. YASINA and V. S. PUD0V, Vysokomol. soyed. AI9: 2083, 1977 (Translated in Polymer Sei. U.S.S.R. 19: 9, 2389, 1977) 4. S. A. REITLINGER, Pro:litsayemost' polimernykh materialov (The Permeability of Polymeric Materials). p. 136, Izd. "Khimiya", 1974
Oxidation of oligoisobutylenes
185~
5. B. I. SAZHIN, ~lektricheskie svoistva polimerov (The Electrical Properties of P o l y m e r s ) , p. 31, Izd. "Khimiya", 1970 6. S. G. K I R Y U S H X I N a n d Yu. A . S H L Y A P N I K O V , D o k l . A k a d . N a u k S S S R 252: 845,
1977 7. F. H. GE1T,, Polimernye monokristally (Polymer Single Crystals). p. 530, Izd. "Khimiya", 1968 (Russian translation) 8. A . P E T E R L I N ,
J. Macromolec.
Sci. B l 1 :
57,
1975
OO32-395Ol79/O8O1-1857507A$010
Polymer Science U.S.S.R. Vol. 21, pp. 1857-1866. O Pergamon Press L~d. 1980. Printed in Poland
O X m A T I O N OF 0LIGOISOBUTYLENES WITH CARBOXYL END GROUPS, AND THE DECARBOXYLATION ASSOCIATED WITH IT* S H . A. ~ASYBULLIN, I. N. ZARIPOV, A. V. DYUL'DEVA a n d I. N. FA[ZUT.T.r~
(Received 26 May 1978) The general relationships found in oxidation of carbon chain polymsrs in solution apply to the oxidation of oligoisobutylene in solution in chlorobenzene. Terminal earboxyl groups in oligoisobutylenes undergo decarboxylation under the action of peroxide radicals and do not affect the total rate of oxidation. The main quantity of C02 is evolved in decomposition of an intermediate product of the moleeular type, formed as a result of uniform attack by peroxide radicals on the methylene groups in the oligomer molecule. The peroxide groups formed in the course of synthesis of the oligoisobutylene, are bound by intramoleeular hydrogen bonds to the carboxyl end groups and consequently are unstable. Their decomposition to free radicals at the beginning of the reaction results in an anomalously high rate of deearboxylation a n d intensification of oxidative degradation of the oligomer. OLIGOISOBUTYLENES ( O I B ' s )
of t h e
CHs
I
O
S
HOOC--CH,--(CH2--C)n--~ CH8
structure CH3
and
I
HO O C - - C H , - - ( C H , - - C ) , - - C H - - C O O H
CH3
OIB -I
I
1
CH, CHa OIB -If
a r e o b t a i n e d b y ozonolysis of i s o b u t y l e n e - d i e n e c o p o l y m e r s [1, 2]. I n c o n t r a s t t o t h e widely used diene c o p o l y m e r s , t h e s a t u r a t e d m a i n c h a i n of O I B ' s s h o u l d i m p a r t high chemical resistance t o these copolymers, w i t h r e s p e c t t o t h e a c t i o n o f h e a t a n d oxygen. On t h e o t h e r h a n d it w o u l d be e x p e c t e d t h a t t h e c a r b o x y l g r o u p s in t h e m a c r o m o l e c u l e , w h i c h u n d e r g o d e c a r b o x y l a t i o n in t h e course o f * Vysokomol. soyed. A21: No. 8, 1688-1696, 1979.