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Control of copolymerization of vinyl butyl ether with some methacrylates
CONTROL OF COPOLYMERIZATION OF VINYL BUTYL ETHEl{ WITH SOME METHACRYLATES* YE. M. SItAIKItUTDIlgOV, B./~. ZIIUBAlgOV, S. I:~. I~AFIKOV a n d S. K ~ . K ~ u s A I ~ o v A S. M. Kirov State University, Kazan
(Received 3 January 1977) A study was made of the effect of condensed aromatic hydrocarbons on radical eopolymerization of vinyl butyl ethers with methyl methacrylate and isopropyl methacrylate initiated with AID with low degrees of conversion in bulk. It was found possible to control the composition of the copolymer on adding 0.01-0.04 mole/1. naphthalene, anthracene and chryseno irate the reaction system. The proportion of low activity vinyl butyl ether units increases in the copolymer formed. The aromatic additives used do not reduce conversion and the intrinsic viscosity of copolymers and do not at the same time form part of copolymer composition. Results are explained from the point of view of forming a donor-accepter complex between the growing radical and an aromatic hydrocarbon molecule. INVESTIGATIONS of recent y e a r s confirm a n increased interest in radical p o l y m e r i z a tion, t h e m a i n t h e o r e t i c a l aspects of which h a v e b e g u n to t a k e s h a p e recently. I t is e x t r e m e l y beneficial, for e x a m p l e , to a d d c o m p o u n d s specially c a p a b l e o f u n d e r g o i n g c o m p l e x f o r m a t i o n w i t h m o n o m e r s a n d extension radicals, in order to c a r r y o u t controlled s y n t h e s i s of p o l y m e r s b y radical p o l y m e r i z a t i o n ; this h a s a m a r k e d effect on r e a c t i v i t y [1-6]. Studies of e x p l a i n i n g t h e role of a r o m a t i c c o m p o u n d s [4-6] are of p a r t i c u l a r interest as these c o m p o u n d s are able to f o r m c o m p l e x e s w i t h charge t r a n s f e r (CCT) in radical p o l y m e r i z a t i o n . H o w e v e r , results in t h e l i t e r a t u r e deal w i t h t h e effect of a r o m a t i c h y d r o c a r b o n s ~s solvents, w h e r e a s t h e i r role as small a d d i t i v e s in radical p o l y m e r i z a t i o n r e m a i n s obscure. A r e p o r t w a s g i v e n [7] of t h e possibility of changing t h e c o m p o s i t i o n of a v i n y l b u t y l e t h e r (VBE) a n d m e t h y l m e t h a e r y l a t e (MMA) e o p o l y m e r in t h e presence of condensed a r o m a t i c h y d r o c a r b o n s . This s t u d y e x a m i n e s t h e eft'oct of t,hese c o m p o u n d s on radical e o p o l y m e r i z a t i o n of v i n y l b u t y l e t h e r w i t h m e t h a e r y l a t e s a n d e x p l a i n s t h e role of e l e c t r o n - d o n o r a d d i t i v e s in this reaction. VBE was washed repeatedly with distilled water, earefully dried over potassium earbonate and twice distilled at atmospheric pressure, b.p. 90.5-9l°/695 ) torr, ~o 1.4025. Commercial MMA was purified by eonventional methods, b.p. 46°/100 torr, .~:(~ 1.4139. '1) AID, the initiator was reerystallized from alcohol, re.p, 102.5°. Analytically pure naphthalene was twice distilled, m.p. 80 ~. Anthracene used was "synthetic suitable for seient, ific studies" obtained after reerystMlization from alcohol, m.p. 216°C. * Vysokomol. soyod. A19: No. 8, 1861-1866, 1977. 2133
YE. M. S~AIKHUTDINOV
2134
et al.
P u r e c h r y s e n e w a s t w i c e r e c r y s t a l l i z e d f r o m alcohol, m . p . 254 °. K i n e t i c s o f c o p o l y m e r i z a t i o n o f V B E w i t h M M A w e r e s t u d i e d d i l a t o m e t r i c a l l y a t 60 ~ i n b u l k in t h e p r e s e n c e o f c o n d e n s e d a r o m a t i c h y d r o c a r b o n s . 5 x 10 -3 mole/1. A I D w a s u s e d as i n i t i a t o r . T h e r e a c t i o n w a s c a r r i e d o u t t o a m a x i m u m c o n v e r s i o n o f 5~/o. T h e c o p o l y m e r f o r m e d was d i s s o l v e d in e t h y l a c e t a t e a n d p r e c i p i t a t e d in methanol.
1.0
z~
5
-
2
!
-d~s
I
0
20
I
¢0
/
I
I
60
0"5
Time, min
Me, mol. fmac//ons
kO
FIG. 2
~FI(L 1
F I o . l. R e l a t i o n b e t w e e n t h e d e g r e e o f c o n v e r s i o n o f V B E a n d MMA m o n o m e r s (1 : 1) a n d t i m e : 1 - - w i t h o u t a d d i t i v e ; 2 - - w i t h n a p h t h a l e n e (3.3 × l 0 -2 mole/l.); 3 - - w i t h a n t h r a c e n e (3"7 X 10 -2 mole/l.); d - - w i t h c h r y s e n e (0.9 >< 10 -2 mole/1.). FIG. 2. Curves s h o w i n g t h e c o m p o s i t i o n o f a V B E - M M A c o p o l y m e r : I - - w i t h o u t a d d i t i v e s ; 2 - - in t h e p r e s e n c e o f 2-3 × 10 -a mole/1, n a p h t h a l e n e ; M 2 - - m o l a r f r a c t i o n o f M M A in theinitial m o n o m e r m i x t u r e , m2 - - m o l a r f r a c t i o n of M M A in t h e c o p o l y m e r .
[DPPH]
10
[DPPH]o
0"5
IO
3O Fro. 3
50 e~lOz mole/[.
~ 1 ~ ~ 15
3 3O
T/me, rain
[ ......
05
FIG. 4
Fzo. 3. V a r i a t i o n in t h e r e l a t i v e a c t i v i t y o f MMA a c c o r d i n g t o n a p h t h a l e n e c o n c e n t r a t i o n c. l~m. 4. V a r i a t i o n o f D P P t t c o n t e n t a c c o r d i n g to t i m e : I - - MMA; 2 - - MMA a n d n a p h t h a l e n e (3.3 × 10 .2 mole/1.), 3 - - V B E ; d - - V B E a n d n a p h t h a l e n e (3.3 × 10 .2 mole/1.) ([DPPH]=, = 1.6 × 10 -a [ A I D ] 0 = 5 × 10 -s mole/l, in all solutions).
C o p o l y m e r i z a t i o n of V B E w i t h m e t h a c r y l a t o s
2135
T h e composition of V B E - M M A c o p o l y m e r s synthesized in t h e presence of n a p h t h a l e n e ~ a s d e t e r m i n e d b y e l e m e n t a r y analysis using I1% a n d N M R spectroscopy; these m e t h o d s s h o w e d satisfactory a g r e e m e n t of results. I n other systems c o p o l y m e r composition w a s t h e r e f o r e d e r i v e d f r o m results of e l e m e n t a r y analysis. Constants of c o p o l y m e r i z a t i o n were d e t e r m i n e d b y t h e M a y o - L e w i s m e t h o d f r o m t h e differential e q u a t i o n of c o p o l y m e r composition. T h e viscosities of benzene solutions of copolymers were m e a s u r e d in an Ostwald viscom e t e r at 20 ° . II% spectra were recorded in t h e range of 1700-1800 cm -1 using a U R - 2 0 s p e c t r o m e t e r in cells of s o d i u m chloride of thickness 0.04 ram. MMA c o n t e n t in the c o p o l y m e r was deter., m i n e d b y m e a s u r i n g b a n d i n t e n s i t y at 1735 cm -~, corresponding to b o n d stretching vibrations of t h e c a r b o n y l group. 1XM1R spectra were o b t a i n e d in an Z X R - 6 0 a p p a r a t u s at r o o m t e m p e r a t u r e and at a f r e q u e n c y of 60 N c / s . H e x a m e t h y l d i s i l o x a n e was the internal standard. To d e t e r m i n e composition, 5Oo c o p o l y m c r solutions in d e h y d r a t e d benzene were used. M M A c o n t e n t in t h e e o p o l y m e r was calculated f r o m t h e r e d u c t i o n of p e a k areas at 6.67 and 6.78 r, t y p i c a l of p r o t o n s of t h e m e t h o x y l group in t h e m i d d l e of h e t c r o t a e t i e and syndiotactie triads, respectively.
Results concerning the effect of various concentrations of aromatic hydrocarbons on the composition and intrinsic viscosity of VBE and I M A eopo]ymer with an initial eqnimoleeular ratio of monomers are shown in Table 1. TABLE
1. EFFECT
OF
I~AI°IITHALE:NE,
ANTHRACENE,
CIIRYSENE
ON
COFOL]'~,IERIZATION ~TB]~ AND M M A (Reaction t i m e 60 rain)
A d d i t i v e c × l0 S, mole/1.
C o p o l y m e r composition, mole °/o
[q], dl/g
VBE
MMA
7-0
93.0
0"98
Without additive
0
Napthalene
0.7 3.3 8.5
7-0 18.0 13.5
93.0 82-0 86.5
1"06 1"02 l'10
Anthracene
2.6 3"7 5"2
17-5 25.0 13.0
82.5 75.0 87-0
0"92 0"94 0'93
Chrysene
0.9 2.5
25.0 18-5
75.0 81.5
0'93 0"92
Table 1 shows that the addition of small amounts of aromatic compounds results in a change in composition of the copolymer obtained. A maximum increase in the proportion of low activity VBE units in the copolymer composition is observed with a naphthalene concentration of 3.3× 10 -~, anthracene concentration of 3.7× 10 -3 and chrysene concentration of 0"9×10 -2 mole/l. A significant change in copolymer composition was confirmed b y NMI% and IR, spectroscopy. The effect observed in the presence of small doses of aromatic
2136
YH. M. SHAIKHUTDINOV el ag.
hydrocarbons is accompanied by some increase in the rate of conversion v of monomers to eopolymer (Fig. 1). Figure 2 shows curves of copolymer composition, plotted in the presence of naphthalene and without additive. I t can be seen t h a t the presence of naphthalene in the system (curve 2) results in a marked reduction in the proportion of MMA TABLE 2. POLYMERIZATION OF MMA PRESENCE OF NAPHTHALENE
IN THE
(Reaction time 25 rain) c × 102,
v × 1 0 s,
mole/1,
mole/1. •sec
4 10 50 100
1"82 2.50 2.50 2"36 2"24
M × 10-s 5.75 6.3I 6.18 6"16 6-31
(m2) in the macromolecule. Copolymerization of VBE with MMA in the presence of 3.7 × 10 -3 mole/1, anthracene and 0.9 × 10 -3 mole/1, chrysene was also carried out with different ratios of initial monomers, in order to evaluate their relative activities. For all systems r l ~ 0 ; r 2 being 11.7±0.5 for VBE-MMA systems; 3.8-4-0.2 for VBE-MMA-naphthalene systems; 1-10-}-0.05 for VBE-MMAanthracene systems and 2.24-0.1 for VBE-MMA-chrysene systems. The value of r2 is reduced considerably in the presence of aromatic additives. A change in the value of r 2 in the presence of additives is in agreement with results of the relative affinity for a methyl radical for naphthalene (22), chrysene (57.5) and anthracene (820) [8]. Figure 3, which shows the relation between the relative activity of MMA and various naphthalene concentrations, illustrates t h a t a sudden reduction is observed in the value of r 2 with a naphthalene concentration of over 0.03 mole/1. A n y further increase in its concentration in the system produces an increase of r2, after which the relative activity of MMA remains practically constant. Experimental results suggest t h a t the variation of the relative activity of MMA is due to the formation of CCT between the growing radical, which ends in a MMA unit and the electron-donor aromatic hydrocarbon. I t should be noted t h a t in the presence of condensed aromatic compounds such as naphthalene, anthracene, chrysene, an extremal relation is observed in the system studied between copolymer composition and the concentration of the additive used (Table 1). The maximum content of VBE in the copolymer is achieved on adding low concentrations of aromatic hydrocarbons. An increase in concentration of the latter increases the proportion of the methaerylate unit in the copolymer [9]. A similar effect, in our view, is due to the fact t h a t in the latter case not only the growing radical, but also the MMA molecule forms
Copolymerization of VBE with methacrylates
2137
complexes with the aromatic hydr oc a r bon molecule, since it is known from the literature t h a t the r e a c t i vi t y of t he monomer increases as a consequence of complex formation [10]. Thus, Bamford and B r u m b y [5] examined the effect of the t y p e of aromatic solvent on the elementary stages of photoinitiated polymerization of MMA and established an increase in reaction rate as a result of T A B L E 3. C O P O L Y M E R I Z A T I O N O F
VBE
WITH
PMA*
IN THE PRESENCE
OF N A P H T H A L E N E
Copolymer composition, mole% VBE PMA
c × i02, mole/1. Without additive 0.7 3.3 6.6
20.0 20-5 34.0 34.0
Conx.rer-
sion, %
0"98
3.7 5.1 4.2 4.0
80.0 79.5 66.0 66.0
[e], dl/g
1"07 I'30 1"28
* The initial ratio of VBE: PMA = 50 : 50, reaction time, 60 min.
a higher rate constant of extension ke and a reduction in the rate constant, of r u p t u r e kr in the presence of halide substituted benzene, benzonitrile and anisole. In order to explain the mechanism of the effect of aromatic hydroearbons, NMA was subjected to homopolymerization under similar conditions in the presence of various eoneentrations of naphthalene. Table 2 shows t h a t in the presence of 4.0 × 10 -2 mole/1, naphthalene reaction rate and the molecular weight of PMMA increase which is, apparently, due to a reduction in the rate constant of r u p tu r e in view of screening the active centre of the macroradical with a naphthalene molecule. I t is possible t h a t the value of lee increases somewhat with high additive concentrations as a consequence of complex formation between the MMA monomer and aromatic hydroearbon, as shown previously [5]. Results confirm the existcnee of a slight donor-acceptor interaction between the growing maeroradieal, which ends with a MMA unit and an aromatic compound _ C00CH3
/\/,~
]
CIL--C(Ct[:;) l I]"
]i
I
cooa
~-/\,/"
I I
To s tu d y the effect of these complex forming agents on copolymerization of VB E with other methacrylic acid esters, VBE was copolymerized with isop r o p y l m e t h a e r y l a t e (PMA) in the presence of naphthalene (Table 3). With a naphthalene concentration of 3.3 × l0 -2 mole/1, an increase is observed in the proportion of VBE units in the copolymer, as in the case of copolymerization of VBE with MMA in the presence of naphthalene. Furthermore, results in Table 3 indicate some increase in conversion and intrinsic viscosity of the copolymer on adding naphthalene to the reaction medium. At the same time
2138
YE. M. SHAIKHUTDINOVet
al.
:naphthalene has practically no effect on intrinsic viscosities of VBE-M_~A copolymers. It is possible that the naphthalene-methacrylate complex proposed reduces the rate constant of rupture to a greater extent as ~ result of the steric .effect, which increases reaction rate, conversion and the viscosity of the copolymer o f VBE with higher methaerylates. No typical absorption bands were found in UV spectra of V B E - m e t h a erylate copolymers synthesized in the presence of condensed aromatic hydrocarbons, which is evidence of their absence from the composition of the copolymer. To confirm the assumption about complex formation between the growing radical and the aromatic hydrocarbon molecule, we studied the effect of naphthalene on radical recombination kinetics of diphenyl-picryl hydrazyl (DPPH) at 60 ° in a MMA solution and VBE with an A I D initi~or. The concentration of D P P H was 1.6× 10 -3 mole/1, and the amount of A I D in all the solutions was 5.0× 10 -3 mole/1. The relation derived between D P P H contents and time in Fig. 4 shows that the proposed naphthalene-MMA complex reduces the activity of the radical, whilst no similar complex is formed in the case of VBE which is confirmed b y the identical E P R spectra of D P P t t in VBE and the V B E - naphthalene system. The effect observed m a y thus be explained b y the acceptor role of the growing radical and the donor behaviour of the aromatic hydrocarbon. Eight types of elementary reaction of chain extension should be considered in this case instead of four ~MI+M,
k',
(1)
,-,M~+M 1 ~', ~M~
(3)
~M~+M~. k'~ ~M~
(4)
,-~M~...D + My k' , ~M~.
(5)
, ~ M ~ . . . D + M z k , ,,~Mi + M , - -k - ~
(6) (7) (8)
Copolymerizatior~ of VBE with methacrylates
2139
w h e r e D is t h e molecule of t h e electron d o n o r a r o m a t i c h y d r o c a r b o n . Since h o m o p o l y m e r i z a t i o n of V B E b y a radical m e c h a n i s m does n o t t a k e place u n d e r t h e conditions used b y us a n d t h e possibility of c o m p l e x f o r m a t i o n b e t w e e n r~dical M~ a n d t h e a d d i t i v e molecule is e x c l u d e d (Fig. 4), r e a c t i o n s (1), (5) ~nd (6) m a y be ignored in practice. Therefore, at least five e l e m e n t a r y r e a c t i o n s t a k e p a r t in chain extension: in a d d i t i o n to c o n v e n t i o n a l re~ctions of e x t e n s i o n (2) - (4) r e a c t i o n s (7) a n d (8) t a k e place. F o r t h e last reaction a r e d u c t i o n in t h e a c t i v i t y of t h e growing MMA radical occurs as ~ result of shielding t h e a c t i v e centre b y t h e molecule of a r o m a t i c h y d r o c a r b o n , consequently, t h e p r o p o r t i o n of V B E units in t h e c o p o l y m e r increases. T h e a u t h o r s are g r a t e f u l to V. A. K a b a n o v ~nd V. P. Z u b o v for discussing t h e results. Translated by E. SEMEI~E REFERENCES
1. V. P. ZUBOV and V. A. KABANOV, Vysokomol. soyed. A13: 1305, 1971 (Tra1~slated ia Polymer Sci. U.S.S.R. 13: 6, 1465, 1971) 2. V. A. KABANOV and D. A. TOPCHIYEV, Vysokomol. soycd. AI3: 1324, 1971 (Trallslated ill Polymer Sci. U.S.S.IZ. 13: 6, 1486, 1971) 3. A. V. RYABOV, Yu. D. SEMCHIKOV, L. A. SMIRNOVA, N. N. SLAVITSKII, N. L. KHVATOVA and V. N. KASHAYEVA, Vysokomol. soyed. A13: 1414, 1971 (TraIlslated in Polymer Sci. U.S.S.I%. 13: 6, 1592, 1971) 4. G. HENRICI-OLIVE and S. OLIVE, Makromolek. Chem. 96: 221, 1966 5. S. H. BAMFORD and S. BI~UMBY, Makromolek. Chem. 105: 122, 1967 6. E. TSUCHIDA and T. TOMONO, Makromolek. Chem. 141: 265, 1971 7. E. M. SKAIKHUTDINOV, B. A. ZHUBANOV an4 S. Kh. KI-IUSAINOVA, Vysokomol. soyed. B15: 869, 1973 (Not trallslated irx Polymer Sci. U.S.S.R.) 8. K. KHIGASI, Kh. BABA and A. REMBAUM, Kvantovaya organicheskaya khimiya (Quantum Orgaifie Chemistry). Izd. "Mir", 1967 9. Yo. M. SHAIKH]JTDINOV, S. Kh. KHUSAINOVA an4 S. P. PIVOVAROV, Preprints 23 Irtterr~atiorxal Symposium oi~ Maeromolecules, Madrid, 1974 10. A. N. PRAVEDNIKOV and S. N. NOVIKOV, Vysokomol. soyed. AI3: 1404, 1971 (Translated in Polymer Sol. U.S.S.I~. 13: 6, 1580, 1971)
(Received 3 January 1977) A study was made of the effect of condensed aromatic hydrocarbons on radical eopolymerization of vinyl butyl ethers with methyl methacrylate and isopropyl methacrylate initiated with AID with low degrees of conversion in bulk. It was found possible to control the composition of the copolymer on adding 0.01-0.04 mole/1. naphthalene, anthracene and chryseno irate the reaction system. The proportion of low activity vinyl butyl ether units increases in the copolymer formed. The aromatic additives used do not reduce conversion and the intrinsic viscosity of copolymers and do not at the same time form part of copolymer composition. Results are explained from the point of view of forming a donor-accepter complex between the growing radical and an aromatic hydrocarbon molecule. INVESTIGATIONS of recent y e a r s confirm a n increased interest in radical p o l y m e r i z a tion, t h e m a i n t h e o r e t i c a l aspects of which h a v e b e g u n to t a k e s h a p e recently. I t is e x t r e m e l y beneficial, for e x a m p l e , to a d d c o m p o u n d s specially c a p a b l e o f u n d e r g o i n g c o m p l e x f o r m a t i o n w i t h m o n o m e r s a n d extension radicals, in order to c a r r y o u t controlled s y n t h e s i s of p o l y m e r s b y radical p o l y m e r i z a t i o n ; this h a s a m a r k e d effect on r e a c t i v i t y [1-6]. Studies of e x p l a i n i n g t h e role of a r o m a t i c c o m p o u n d s [4-6] are of p a r t i c u l a r interest as these c o m p o u n d s are able to f o r m c o m p l e x e s w i t h charge t r a n s f e r (CCT) in radical p o l y m e r i z a t i o n . H o w e v e r , results in t h e l i t e r a t u r e deal w i t h t h e effect of a r o m a t i c h y d r o c a r b o n s ~s solvents, w h e r e a s t h e i r role as small a d d i t i v e s in radical p o l y m e r i z a t i o n r e m a i n s obscure. A r e p o r t w a s g i v e n [7] of t h e possibility of changing t h e c o m p o s i t i o n of a v i n y l b u t y l e t h e r (VBE) a n d m e t h y l m e t h a e r y l a t e (MMA) e o p o l y m e r in t h e presence of condensed a r o m a t i c h y d r o c a r b o n s . This s t u d y e x a m i n e s t h e eft'oct of t,hese c o m p o u n d s on radical e o p o l y m e r i z a t i o n of v i n y l b u t y l e t h e r w i t h m e t h a e r y l a t e s a n d e x p l a i n s t h e role of e l e c t r o n - d o n o r a d d i t i v e s in this reaction. VBE was washed repeatedly with distilled water, earefully dried over potassium earbonate and twice distilled at atmospheric pressure, b.p. 90.5-9l°/695 ) torr, ~o 1.4025. Commercial MMA was purified by eonventional methods, b.p. 46°/100 torr, .~:(~ 1.4139. '1) AID, the initiator was reerystallized from alcohol, re.p, 102.5°. Analytically pure naphthalene was twice distilled, m.p. 80 ~. Anthracene used was "synthetic suitable for seient, ific studies" obtained after reerystMlization from alcohol, m.p. 216°C. * Vysokomol. soyod. A19: No. 8, 1861-1866, 1977. 2133
YE. M. S~AIKHUTDINOV
2134
et al.
P u r e c h r y s e n e w a s t w i c e r e c r y s t a l l i z e d f r o m alcohol, m . p . 254 °. K i n e t i c s o f c o p o l y m e r i z a t i o n o f V B E w i t h M M A w e r e s t u d i e d d i l a t o m e t r i c a l l y a t 60 ~ i n b u l k in t h e p r e s e n c e o f c o n d e n s e d a r o m a t i c h y d r o c a r b o n s . 5 x 10 -3 mole/1. A I D w a s u s e d as i n i t i a t o r . T h e r e a c t i o n w a s c a r r i e d o u t t o a m a x i m u m c o n v e r s i o n o f 5~/o. T h e c o p o l y m e r f o r m e d was d i s s o l v e d in e t h y l a c e t a t e a n d p r e c i p i t a t e d in methanol.
1.0
z~
5
-
2
!
-d~s
I
0
20
I
¢0
/
I
I
60
0"5
Time, min
Me, mol. fmac//ons
kO
FIG. 2
~FI(L 1
F I o . l. R e l a t i o n b e t w e e n t h e d e g r e e o f c o n v e r s i o n o f V B E a n d MMA m o n o m e r s (1 : 1) a n d t i m e : 1 - - w i t h o u t a d d i t i v e ; 2 - - w i t h n a p h t h a l e n e (3.3 × l 0 -2 mole/l.); 3 - - w i t h a n t h r a c e n e (3"7 X 10 -2 mole/l.); d - - w i t h c h r y s e n e (0.9 >< 10 -2 mole/1.). FIG. 2. Curves s h o w i n g t h e c o m p o s i t i o n o f a V B E - M M A c o p o l y m e r : I - - w i t h o u t a d d i t i v e s ; 2 - - in t h e p r e s e n c e o f 2-3 × 10 -a mole/1, n a p h t h a l e n e ; M 2 - - m o l a r f r a c t i o n o f M M A in theinitial m o n o m e r m i x t u r e , m2 - - m o l a r f r a c t i o n of M M A in t h e c o p o l y m e r .
[DPPH]
10
[DPPH]o
0"5
IO
3O Fro. 3
50 e~lOz mole/[.
~ 1 ~ ~ 15
3 3O
T/me, rain
[ ......
05
FIG. 4
Fzo. 3. V a r i a t i o n in t h e r e l a t i v e a c t i v i t y o f MMA a c c o r d i n g t o n a p h t h a l e n e c o n c e n t r a t i o n c. l~m. 4. V a r i a t i o n o f D P P t t c o n t e n t a c c o r d i n g to t i m e : I - - MMA; 2 - - MMA a n d n a p h t h a l e n e (3.3 × 10 .2 mole/1.), 3 - - V B E ; d - - V B E a n d n a p h t h a l e n e (3.3 × 10 .2 mole/1.) ([DPPH]=, = 1.6 × 10 -a [ A I D ] 0 = 5 × 10 -s mole/l, in all solutions).
C o p o l y m e r i z a t i o n of V B E w i t h m e t h a c r y l a t o s
2135
T h e composition of V B E - M M A c o p o l y m e r s synthesized in t h e presence of n a p h t h a l e n e ~ a s d e t e r m i n e d b y e l e m e n t a r y analysis using I1% a n d N M R spectroscopy; these m e t h o d s s h o w e d satisfactory a g r e e m e n t of results. I n other systems c o p o l y m e r composition w a s t h e r e f o r e d e r i v e d f r o m results of e l e m e n t a r y analysis. Constants of c o p o l y m e r i z a t i o n were d e t e r m i n e d b y t h e M a y o - L e w i s m e t h o d f r o m t h e differential e q u a t i o n of c o p o l y m e r composition. T h e viscosities of benzene solutions of copolymers were m e a s u r e d in an Ostwald viscom e t e r at 20 ° . II% spectra were recorded in t h e range of 1700-1800 cm -1 using a U R - 2 0 s p e c t r o m e t e r in cells of s o d i u m chloride of thickness 0.04 ram. MMA c o n t e n t in the c o p o l y m e r was deter., m i n e d b y m e a s u r i n g b a n d i n t e n s i t y at 1735 cm -~, corresponding to b o n d stretching vibrations of t h e c a r b o n y l group. 1XM1R spectra were o b t a i n e d in an Z X R - 6 0 a p p a r a t u s at r o o m t e m p e r a t u r e and at a f r e q u e n c y of 60 N c / s . H e x a m e t h y l d i s i l o x a n e was the internal standard. To d e t e r m i n e composition, 5Oo c o p o l y m c r solutions in d e h y d r a t e d benzene were used. M M A c o n t e n t in t h e e o p o l y m e r was calculated f r o m t h e r e d u c t i o n of p e a k areas at 6.67 and 6.78 r, t y p i c a l of p r o t o n s of t h e m e t h o x y l group in t h e m i d d l e of h e t c r o t a e t i e and syndiotactie triads, respectively.
Results concerning the effect of various concentrations of aromatic hydrocarbons on the composition and intrinsic viscosity of VBE and I M A eopo]ymer with an initial eqnimoleeular ratio of monomers are shown in Table 1. TABLE
1. EFFECT
OF
I~AI°IITHALE:NE,
ANTHRACENE,
CIIRYSENE
ON
COFOL]'~,IERIZATION ~TB]~ AND M M A (Reaction t i m e 60 rain)
A d d i t i v e c × l0 S, mole/1.
C o p o l y m e r composition, mole °/o
[q], dl/g
VBE
MMA
7-0
93.0
0"98
Without additive
0
Napthalene
0.7 3.3 8.5
7-0 18.0 13.5
93.0 82-0 86.5
1"06 1"02 l'10
Anthracene
2.6 3"7 5"2
17-5 25.0 13.0
82.5 75.0 87-0
0"92 0"94 0'93
Chrysene
0.9 2.5
25.0 18-5
75.0 81.5
0'93 0"92
Table 1 shows that the addition of small amounts of aromatic compounds results in a change in composition of the copolymer obtained. A maximum increase in the proportion of low activity VBE units in the copolymer composition is observed with a naphthalene concentration of 3.3× 10 -~, anthracene concentration of 3.7× 10 -3 and chrysene concentration of 0"9×10 -2 mole/l. A significant change in copolymer composition was confirmed b y NMI% and IR, spectroscopy. The effect observed in the presence of small doses of aromatic
2136
YH. M. SHAIKHUTDINOV el ag.
hydrocarbons is accompanied by some increase in the rate of conversion v of monomers to eopolymer (Fig. 1). Figure 2 shows curves of copolymer composition, plotted in the presence of naphthalene and without additive. I t can be seen t h a t the presence of naphthalene in the system (curve 2) results in a marked reduction in the proportion of MMA TABLE 2. POLYMERIZATION OF MMA PRESENCE OF NAPHTHALENE
IN THE
(Reaction time 25 rain) c × 102,
v × 1 0 s,
mole/1,
mole/1. •sec
4 10 50 100
1"82 2.50 2.50 2"36 2"24
M × 10-s 5.75 6.3I 6.18 6"16 6-31
(m2) in the macromolecule. Copolymerization of VBE with MMA in the presence of 3.7 × 10 -3 mole/1, anthracene and 0.9 × 10 -3 mole/1, chrysene was also carried out with different ratios of initial monomers, in order to evaluate their relative activities. For all systems r l ~ 0 ; r 2 being 11.7±0.5 for VBE-MMA systems; 3.8-4-0.2 for VBE-MMA-naphthalene systems; 1-10-}-0.05 for VBE-MMAanthracene systems and 2.24-0.1 for VBE-MMA-chrysene systems. The value of r2 is reduced considerably in the presence of aromatic additives. A change in the value of r 2 in the presence of additives is in agreement with results of the relative affinity for a methyl radical for naphthalene (22), chrysene (57.5) and anthracene (820) [8]. Figure 3, which shows the relation between the relative activity of MMA and various naphthalene concentrations, illustrates t h a t a sudden reduction is observed in the value of r 2 with a naphthalene concentration of over 0.03 mole/1. A n y further increase in its concentration in the system produces an increase of r2, after which the relative activity of MMA remains practically constant. Experimental results suggest t h a t the variation of the relative activity of MMA is due to the formation of CCT between the growing radical, which ends in a MMA unit and the electron-donor aromatic hydrocarbon. I t should be noted t h a t in the presence of condensed aromatic compounds such as naphthalene, anthracene, chrysene, an extremal relation is observed in the system studied between copolymer composition and the concentration of the additive used (Table 1). The maximum content of VBE in the copolymer is achieved on adding low concentrations of aromatic hydrocarbons. An increase in concentration of the latter increases the proportion of the methaerylate unit in the copolymer [9]. A similar effect, in our view, is due to the fact t h a t in the latter case not only the growing radical, but also the MMA molecule forms
Copolymerization of VBE with methacrylates
2137
complexes with the aromatic hydr oc a r bon molecule, since it is known from the literature t h a t the r e a c t i vi t y of t he monomer increases as a consequence of complex formation [10]. Thus, Bamford and B r u m b y [5] examined the effect of the t y p e of aromatic solvent on the elementary stages of photoinitiated polymerization of MMA and established an increase in reaction rate as a result of T A B L E 3. C O P O L Y M E R I Z A T I O N O F
VBE
WITH
PMA*
IN THE PRESENCE
OF N A P H T H A L E N E
Copolymer composition, mole% VBE PMA
c × i02, mole/1. Without additive 0.7 3.3 6.6
20.0 20-5 34.0 34.0
Conx.rer-
sion, %
0"98
3.7 5.1 4.2 4.0
80.0 79.5 66.0 66.0
[e], dl/g
1"07 I'30 1"28
* The initial ratio of VBE: PMA = 50 : 50, reaction time, 60 min.
a higher rate constant of extension ke and a reduction in the rate constant, of r u p t u r e kr in the presence of halide substituted benzene, benzonitrile and anisole. In order to explain the mechanism of the effect of aromatic hydroearbons, NMA was subjected to homopolymerization under similar conditions in the presence of various eoneentrations of naphthalene. Table 2 shows t h a t in the presence of 4.0 × 10 -2 mole/1, naphthalene reaction rate and the molecular weight of PMMA increase which is, apparently, due to a reduction in the rate constant of r u p tu r e in view of screening the active centre of the macroradical with a naphthalene molecule. I t is possible t h a t the value of lee increases somewhat with high additive concentrations as a consequence of complex formation between the MMA monomer and aromatic hydroearbon, as shown previously [5]. Results confirm the existcnee of a slight donor-acceptor interaction between the growing maeroradieal, which ends with a MMA unit and an aromatic compound _ C00CH3
/\/,~
]
CIL--C(Ct[:;) l I]"
]i
I
cooa
~-/\,/"
I I
To s tu d y the effect of these complex forming agents on copolymerization of VB E with other methacrylic acid esters, VBE was copolymerized with isop r o p y l m e t h a e r y l a t e (PMA) in the presence of naphthalene (Table 3). With a naphthalene concentration of 3.3 × l0 -2 mole/1, an increase is observed in the proportion of VBE units in the copolymer, as in the case of copolymerization of VBE with MMA in the presence of naphthalene. Furthermore, results in Table 3 indicate some increase in conversion and intrinsic viscosity of the copolymer on adding naphthalene to the reaction medium. At the same time
2138
YE. M. SHAIKHUTDINOVet
al.
:naphthalene has practically no effect on intrinsic viscosities of VBE-M_~A copolymers. It is possible that the naphthalene-methacrylate complex proposed reduces the rate constant of rupture to a greater extent as ~ result of the steric .effect, which increases reaction rate, conversion and the viscosity of the copolymer o f VBE with higher methaerylates. No typical absorption bands were found in UV spectra of V B E - m e t h a erylate copolymers synthesized in the presence of condensed aromatic hydrocarbons, which is evidence of their absence from the composition of the copolymer. To confirm the assumption about complex formation between the growing radical and the aromatic hydrocarbon molecule, we studied the effect of naphthalene on radical recombination kinetics of diphenyl-picryl hydrazyl (DPPH) at 60 ° in a MMA solution and VBE with an A I D initi~or. The concentration of D P P H was 1.6× 10 -3 mole/1, and the amount of A I D in all the solutions was 5.0× 10 -3 mole/1. The relation derived between D P P H contents and time in Fig. 4 shows that the proposed naphthalene-MMA complex reduces the activity of the radical, whilst no similar complex is formed in the case of VBE which is confirmed b y the identical E P R spectra of D P P t t in VBE and the V B E - naphthalene system. The effect observed m a y thus be explained b y the acceptor role of the growing radical and the donor behaviour of the aromatic hydrocarbon. Eight types of elementary reaction of chain extension should be considered in this case instead of four ~MI+M,
k',
(1)
,-,M~+M 1 ~', ~M~
(3)
~M~+M~. k'~ ~M~
(4)
,-~M~...D + My k' , ~M~.
(5)
, ~ M ~ . . . D + M z k , ,,~Mi + M , - -k - ~
(6) (7) (8)
Copolymerizatior~ of VBE with methacrylates
2139
w h e r e D is t h e molecule of t h e electron d o n o r a r o m a t i c h y d r o c a r b o n . Since h o m o p o l y m e r i z a t i o n of V B E b y a radical m e c h a n i s m does n o t t a k e place u n d e r t h e conditions used b y us a n d t h e possibility of c o m p l e x f o r m a t i o n b e t w e e n r~dical M~ a n d t h e a d d i t i v e molecule is e x c l u d e d (Fig. 4), r e a c t i o n s (1), (5) ~nd (6) m a y be ignored in practice. Therefore, at least five e l e m e n t a r y r e a c t i o n s t a k e p a r t in chain extension: in a d d i t i o n to c o n v e n t i o n a l re~ctions of e x t e n s i o n (2) - (4) r e a c t i o n s (7) a n d (8) t a k e place. F o r t h e last reaction a r e d u c t i o n in t h e a c t i v i t y of t h e growing MMA radical occurs as ~ result of shielding t h e a c t i v e centre b y t h e molecule of a r o m a t i c h y d r o c a r b o n , consequently, t h e p r o p o r t i o n of V B E units in t h e c o p o l y m e r increases. T h e a u t h o r s are g r a t e f u l to V. A. K a b a n o v ~nd V. P. Z u b o v for discussing t h e results. Translated by E. SEMEI~E REFERENCES
1. V. P. ZUBOV and V. A. KABANOV, Vysokomol. soyed. A13: 1305, 1971 (Tra1~slated ia Polymer Sci. U.S.S.R. 13: 6, 1465, 1971) 2. V. A. KABANOV and D. A. TOPCHIYEV, Vysokomol. soycd. AI3: 1324, 1971 (Trallslated ill Polymer Sci. U.S.S.IZ. 13: 6, 1486, 1971) 3. A. V. RYABOV, Yu. D. SEMCHIKOV, L. A. SMIRNOVA, N. N. SLAVITSKII, N. L. KHVATOVA and V. N. KASHAYEVA, Vysokomol. soyed. A13: 1414, 1971 (TraIlslated in Polymer Sci. U.S.S.I%. 13: 6, 1592, 1971) 4. G. HENRICI-OLIVE and S. OLIVE, Makromolek. Chem. 96: 221, 1966 5. S. H. BAMFORD and S. BI~UMBY, Makromolek. Chem. 105: 122, 1967 6. E. TSUCHIDA and T. TOMONO, Makromolek. Chem. 141: 265, 1971 7. E. M. SKAIKHUTDINOV, B. A. ZHUBANOV an4 S. Kh. KI-IUSAINOVA, Vysokomol. soyed. B15: 869, 1973 (Not trallslated irx Polymer Sci. U.S.S.R.) 8. K. KHIGASI, Kh. BABA and A. REMBAUM, Kvantovaya organicheskaya khimiya (Quantum Orgaifie Chemistry). Izd. "Mir", 1967 9. Yo. M. SHAIKH]JTDINOV, S. Kh. KHUSAINOVA an4 S. P. PIVOVAROV, Preprints 23 Irtterr~atiorxal Symposium oi~ Maeromolecules, Madrid, 1974 10. A. N. PRAVEDNIKOV and S. N. NOVIKOV, Vysokomol. soyed. AI3: 1404, 1971 (Translated in Polymer Sol. U.S.S.I~. 13: 6, 1580, 1971)