The phase state of the system and its effect on the steric copolymerization kinetics of triethylene glycol dimethacrylate (TGM-3) with styrene

Sterie copolymerization kinetics of TGM-3 with styrene

657

REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

R. A. A. MUZZARELLT; Natural Chelating Polymers 55: 83, 1973 K. NAGASAWA, H. WATANABE and A. OGANO, J. Chromatogr. 47: 408, 1970 BAO-CHLMIN, Khim. volokna, No. 3, 39, 1960 British Pat. 930765, 1963; Chem. Abs. 59: 11758, 1963 Ye. A. PLISKO, D. A. NUD'GA and S. N. DANILOV, Usp. khim. 46: 1470, 1977 T. ASTRUP, I. GALSMAR and M. VOLKERT, Acta Physiol. Scand. 8: 215, 1944; Chem. Abs. 39: 4976, 1945 A. B. FOSTER and J. M. WEBLER, Adv. Carbohydr. Chem. 15: 371, 1960 P. W. KENT, Comparative Biochem. 7: 93, 1964 F. SHAFIZADEH, Adv. Carbohydr. Chem. 23: 419, 1968 W. D. MAJOR, Tappi 41: 530, 1958 E. J. MURPHY, J. Polymer Sci. 58: 649, 1962 S. L. MADORSKY, V. E. HART and S. STRAITS, J. Res. Nat. Bur. Standards 46:343 1956 K. T. WALTER, J. Polymer Sci. C6: 65, 1964 D. F. ARSENEAN, Canad. J. Chem. 49: 632, 1971 S. HERNADI, Papiripar 18: 50, 1974 O. P. GOLOVA, A. P. PAKHOMOV, Ye. A. ANDRIEVSKAYA and R. G. KRYLOVA, Dokl. Akad. Nauk SSSR 115: 1122, 1957 I. K. WALKER, W. J. HARRISON and H. FAY JACKSON, N. Z. J. Sci. 13: 623, 1970; 14: 925, 1971 V. V. YEDEMSKAYA, Dissertation, Moscow, 1973

Polymer Science U.S.S.R. Vol. 22, pp. 657-663. (~) Pergamon Press Ltd. 1981. Printed in Poland

0032-3950/80/0301-0657507.50/0

THE PHASE STATE OF THE SYSTEM AND ITS EFFECT ON THE STERIC COPOLYMERIZATION KINETICS OF TRIETHYLENE GLYCOL DIMETHACRYLATE (TGM-3) WITH STYRENE* N. M. BOL'BIT Branch of L. Ya. Karpov Research Institute of Physical C h e m i s t r y

(Received 30 November 1978} A number of anomalous (in comparison with ideal) mechanisms of the experi. mental steric copolyrnerizations of ethylene glycol dimethacrylate (TGM-3) with styrene has been found to be explained by the hetero-phase type of process caused by the micro-seggregation in the crosslinked aggregate-monomer mixture system; this has been established on the basis of the comparative analysis of the molecular weights and the composition of the copolymers isolated from the copolymerizates. THE RESULTS of s t u d y i n g t h e m e c h a n i s m of t h e s t e r i c c o p o l y m e r i z a t i o n of t h e u n s a t u r a t e d , b i f u n c t i o n a l T G M - 3 w i t h s t y r e n e (St) w h e n 3 d i f f e r e n t o r i g i n a l ¢ o m o n o m e r c o m p o s i t i o n s h a d b e e n u s e d [1, 2] were e s t a b l i s h e d b y t h e m e t h o d * Vysokomol. soyed. A22: No. 3, 595-600, 1980.

658

N . M . BoL'~I~

o f characteristic copolymers (CHCP). T h e statm o f phase ratio in t h e s~eric eop o l y m e r i z a t e - m o n o m e r m i x t u r e s y s t e m w a s a s s u m e d t o h a v e a decisive e f f e c t o f t h e progress o f t h e process a t each r e a c t i o n stage in a n a t t e m p t to clarify t h e m e c h a n i s m o f changes f r o m the a v e r a g e mol.wt., t h e composition a n d the r a t e o f t h e reaction. As e°0o r a d i a t i o n was the c o n t i n u o u s ' i n i t i a t i o n source a n d the rate. o f t h e l a t t e r was p r a c t i c a l l y the same in b o t h t h e m e n t i o n e d micro-phases, a n i m p o r t a n t source of f u r t h e r i n f o r m a t i o n o f h o w reliable our a s s u m p t i o n is m u s t be identical e x p e r i m e n t a l results f r o m t h e C H O P m e t h o d w h e n identical conditions are used. W e selected the r e d o x i n i t i a t i o n whose m a i n a d v a n t a g e is. a large e n o u g h r a t e o f radicals g e n e r a t i o n a t r o o m t e m p e r a t u r e , i.e. t h e t e m p e r a t u r e used earlier for the ?-ray i n i t i a t e d copolymerization; the i n i t i a t o r c o n c e n t r a tion was such t h a t t h e t o t a l r a t e of gel f o r m a t i o n was similar in b o t h cases. EXPERIMENTAL

The original compositions of the comonomers were the same in this series of tests as in an earlier one [2], i.e. a styrene content by weight of: x0=0"17, 0.45 and 0.77 (or molar fractions of 0.22, 0.52 and 0.82 respectively; as the TGM-3 molecule contains 2 double. bonds, only half the mol.wt, is used in the calculations). A 1% w/w content of initiator was used, namely benzoyl peroxide, with diethylamine as the reducing agent; their molar ratio was 1 : 0.3. The thermo-setting of the samples under vacuum was carried out in ampoules placed for a controlled time in an oven at 26°C. All the preparations for the CHCP' used on the gel isolated from each stage and the analytical methods used were described in previous communications [1-3]. Please note that the characteristic copolymer (CHCP) is the methylated hydrolysis product of the steric network in which the acrylate group is, involved. This is the styrene-methylmethacrylate copolymer in our case. RESULTS

The kinetic curves for conversion as a f u n c t i o n of time, the a v e r a g e composN t i o n of t h e CHCP, a n d t h e av.mol.wt. ~rv d e t e r m i n e d b y v i s c o m e t r y [2] as a. f u n c t i o n of the conversion are given in Figs. 1 a n d 2 for the 3 initial s t y r e n e c o n c e n t r a t i o n s in the c o m o n o m e r . W e shall n o w e x a m i n e these functions s e p a r a t e l y for each x 0 value a n d r e f e r a t t h e same time to those [2] f o u n d in the case of initiation b y ?-rays; a comparat i v e analysis will also be made. 1. x0~-0.17 (Figs. 1, 2, curve 1). T h e M - c o n v e r s i o n functions are v e r y similar; ~1~ ~s a linear f u n c t i o n o f conversion u p to 9 0 % in t h e case o f a ?-initiation, while t h e ~lTv increase in the case of chemical initiation is close to exponential. W e g i v e a t first the f o r m a l kinetics as a m e a n s o f explaining the f o u n d mechanisms. As prev i o u s l y [2] we use the a n a l o g y b e t w e e n a steric a n d a n emulsion p o l y m e r i z a t i o n ; this m a k e s physical sense as a p o l y m e r i z i n g s y s t e m can be r e g a r d e d a t fairly low conversions as consisting o f crosslinked aggregates, i.e. globules, which a r e dispersed in the m o n o m e r m i x t u r e [4], or as a latex. T h e n u m b e r of low a c t i v i t y radicals on the n e t w o r k shows a n a l m o s t linear increase with conversion in the, radiolysis of such a h e t e r o - p h a s e system, i.e. the effective rate of i n i t i a t i o a

Steric eopolymerization kinetics of TGM-3 with styrene

65~

w~7)~ 1--~(t). The propagation rate Wpz eonst [2] a n d the polymerization efficiency ~n=2Wp/Wl [6] also linear function of ~,. There is an exponential d r o p of the initiator concentration in the case o£ a redox system because of the peroxide decomposition. B y considering w, ~ const in this case (Fig. 2b; curve 1) u p to an about 90% conversion, the effective wi as a function of time and the molecular weight of the eopolymer component in the network as a function of conversion will not run parallel.

u2, %

100E 60~3

Z

20 8, i q

, 2r

I

, i ql IZ Time, hp

i

i

(z), I(1) 61 20 (3)

F~G. 1. Conversion as a function of time for the copolymerization of styrene-TGl~I-3 mixtures. Benzoyl peroxide and dimethylamine as initiation mixture at molar ratios of 1 : 0.3 (1% w/w), 26°C. The composition (x0) here and in Fig. 2 is: 1--0.17; 2--0.77; 3--0-45. The steric polymerization (o1' copolymerization) is said to b e a variant [5] of the "acrylonitrile" type hetero-phase process, in which the propagation is the result of a monomer polymerization on tile surface or in the bulk of the swelling monomer-polymer gel particles (globules), but also of the maeromolecules, including the macro-radicals, being trapped. The true initiation b y a chemical initiator chiefly takes place in solution, although the compound can also be present in the gel. The radiation initiated process involves both the phases, but there is a difference in the radicals efficiency. The gradual change in the concentrations of the free and the trapped radicals (those in the globules) has as its consequence a growth without termination of a proportion of the trapped chains. Their quanti t y increases as the initiator is consumed, so t h a t the process finally changes to a continuous live chain propagation. The initiation specifics make an impression on the behaviour of the system in later conversion stages; the y-irradiation causes a decomposition of the polymerizate and a My decrease [2]. In a chemical initiation, when the conversion

1500

N.M.

BOL'BIT

to the gel is almost 100%, there in a considerable increase in mol.wt. (by a factor of 1-5) of the CHCP. Infrared spectroscopy showed t h e double bond content of the TGM-3 to still decrease in time at this stage, but the rate of this is slight (about 3~o in 2 days), so that the ~ rises from 10e to 1.5× l0 s. The diffusion of the monomer is sterically hindered owing to the fairly large rigidity of the ~Iu 10"5 ,

x%

12

7

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2 ~'

GO 5 3

3 20 1

20

[

I

80

1

¢J,%

I

I00

o

I

20

I

I

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cp,% 100

I~zG. 2. T h e a v e r a g e composition x (a) a n d t h e ~rv of t h e C H C P (b) as functions o f conversion ¢v in t h e c o p o l y m e r i z a t i o n of s t y r e n e - T G M - 3 m i x t u r e s .

¢rosslinked aggregates when the styrene content is low, so that globular growth occurs chiefly on the surface. The double bonds of TGM-3 attached to the network, or embedded in the nuclei of the globules, arc therefore incapable of polymerizing in the process time, but the macro-radicals present at the surface are \ capable of a diffusion regulated mutual termination. Ham [8] showed the main impact on the termination to be made by a eriss-cross type of termination by recombination in the styrene copolymerization with methyl methacrylate (the TGM-3 analogue). T h e number of terminations by disproportionation fell from 0-4 to zero on changing the molar fraction of methyl methacrylate from 0.95 in the original composition to 0.3. The 1.5 fold increase in ~rv found in our experiments at constant CItCP composition is in excellent agreement with these results. Let us now turn to the results about the conversion of the average styrene -content in the eopolymer. The calculation of the rl/r~, activity ratio (index 1 refers to styrene) at about 5% conversion, when the consistency of the system is still close to that of a solution for 3 values of x0, was found according to the described scheme [2] to give rl =0.7 and r~-~0.8. The same calculation yielded for the radiation-izdtiated copolymerization r~=0.4 and r2~0"6. The result is sensible in both cases, i.e. r=
Sterie copolymerization kinetics of TGM-3 with styrene

661

with conversion when x0----0.17. While the experimental x-g/ curves are of the described type for a y-initiated process [2], a chemical initiation gives x ~ c o n s t to almost a 96% conversion, b u t x afterwards increases to 0.25 (Fig. 2a, curve 1). Such an anomalous behaviour is caused, in our opinion, b y the following: value r 2 > r 1 at first, i.e. the more reactive TGM-3 monomer is more rapidly consumed. Secondly, the addition of one double bond results in a sudden mobility loss of the " a t t a c h e d " bonds, and thirdly, there is a separation into phases at some polymer content as in any polymer-solvent system. A macro-separation is not possible in a sterie or co-polymerization, b u t there is a micro-syneresis, i.e. a displacement of the "odd" (in the thermodynamic sense) solvent from the steric aggregate, namely of the monomer mixture in our case. The micro-syneresis can occur fairly early only in the case of styrene for the first two reasons mentioned (when ~----20-30% , as Wp is constant in this range and the slope of the My increase becomes steeper; Figs. 1 and 2b, curve 1). T h e overall non-additive process rate consists of the rates in both the micro-phases, b u t that in the globular phase is much larger owing to the suppression of termination, while that in the spaces between the globules (chiefly styrene) shows an exponential drop of the initiation rate due to the benzoyl peroxide decomposition. T h e more or less constant diffusion current of styrene into the globule'ensures the constancy of x up to large {amost 96%) conversions. The TGM-3 becomes "inactivated" for sterie reasons at this stage and the styrene not reacted at that time takes over; its content rapidly increases in the copolymer and x rises from 0.2] to 0.25. T h e physics of the microseparation and the subsequent diffusion controlled mass transfer of the reactive monomer in the chemically initiated process thus result in a non-ideal average composition of the eopolymer component of the network. The y-radiation initiated process, in contrast, is characterized b y a continuous radicals generation in each micro-phase and the composition as a function of conversion is "normal". 2. x0=0.45 (Figs. 1, 2, curve 3). The mol.wt. _~¢of the copolymer component in the network also increases exponentially at this composition in the ~ ~ 0-30 range, i.e. is inversely proportional to the cmTent initiator concentration. The gelling in the 30-45% conversion range, caused b y the micro-separation of the system, which transfers the monomers (mainly styrene) from the sterie reaction space into the space between the globules is the reason for the maximum of the propagation rate being reached, a linear /~v increase and some drop of the styrene content in the copolymer. It must not be forgotten that x ought to increase with conversion in an ideal copolymerization, When xa=0"33 (azeotrope composition), as well as at x0=0.45. The reason is the preferential consumption of the more reactive TGM-3 monomer. The situation (at ~>45% ) is subsequently such that two diffusion controlled reactions determine the course of the process, namely a) the styrene penetration from the inter-globular space into the erosslinked aggregates, which is the main area in which copolymerization takes place, and the entry of low reactivity TGM-3 double bonds into the network; b) a mutual termination of the macro-

662

N.M.

BOL'BIT

radicals which grow through the globular surface. Remember t h a t the network aggregates are here less dense in comparison with compositions deficient in styrene, and the rate of the bimolecular termination is correspondingly larger. The simultaneous appearance of the two inhibited propagation and termination reactions results in a psuedo-stationary state in the range ~,=45-95%, in which wp=const a n d / ~ v ~ const. The range of the ridge on the M v - ~ curves (Fig. 2b, curve 3) does not extent into the critical conversion range in a r-initiated process however, and there is a linear mol. wt. increase of the copolymer at ~ > 60%. One c a n now say wit~ greater certainty than before [1] t h a t the effect is due to the continuous radicals generation- which increases that on the network in parallel with ~ and increases the part played b y the graft copolymerization not to be found when a chemical initiator is used. The styrene content gradually increases in the pseudo-stationary range from 0.46 to 0.52 because the fairly large quantity of the more reactive TGM-3 was utilized in the gelling; the x - ~ curve therefore shows a fairly distinct minimum at ~ 45%. At large gelling rates, when the TGM-3 double bonds are eliminated from the reaction (which happens according to I R spectroscopy at an about 80% conversion of the unsaturated ester bonds), the still unreacted styrene will "start to play a part", and the value of x will again increase (from 0.52 to 0.62) although z~~ 5 % , which involves a period of about 10hr. The apparently second rate dependence of the copolymer composition on conversion is thus fairly convincingly explained. The jump in the copolymer composition at the end of the r-initiated reaction at x0-~ 0.45 occurs for the same reasons [2] but could not be explained at the time. 3. x0~--~77 (Figs. 1, 2, curve 2). The lack of any principal difference in the ~-t, x - ~ , and M v - ~ functions obtained here and before [2], i.e. the practical identity, of the mechanisms of the processes developing during the copolymerization of such a composition when both the types of initiation are used, permit the conclusion of the kinetics depending on the styrene excess. This conclusion is strongly supported by the analysis of the homopolymerization kinetics of styrene initiated b y radiation or chemically [9-11]. Two zones of .~v constancy exist in all four of the above cases and these are separated from each other by a fairly narrow zone of distinct gelling at ~--~40% (in a copolymerization with TGM-3) and ~ 60~/o (in the styrene homopolymerization) where there is a rapid increase of the production rate and of the mol.wt, of the polymerizate. The true network formed b y chemical or physical joints with the monomer included in them, and clue to phase conversion, results in a substantial inhibition of the mutual termination b y the macro-ra~licals. The subsequent drop of the rate gives rise to the second /14v constancy. More detail about this is given elsewhere [2]. The styrene content of the CHCP increases with conversion and follows the rules of an ideal copolymerization of a binary system with xa~0.33. The conclusion reached from the described results is t h a t a series of anomalous experimental principles of the steric copolymerization of TGM-3 with

Steric copolymerization kinetics of TGM-3 with styrene

663

the vinyl monomer, compared with an ideal process, is the hetero-phase t y p e of process due to a micro-separation in the crosslinked aggregate-monomer mixture system. The work reported here demonstrates the usefulness of the CHCP method, especially in conjunction with the analysis of the results got after using two methods of initiation. The questions connected with the change in the progress of the eopolymerization having a "normal" start and then becoming anomalous due to the hetero-phase nature of the system, were dealt with in detail by Myagchenkov and co-workers [12]. The authors thank S. Ya. Frenkel for valuable advice and the unexpected and new treatment of the results. This aspect will be dealt/with in a separate publication. Translated by K. A. A L ~ REFERENCES

1. N. M. BOL'BIT and Yu. A. CItlKIN, Vysokomol. soyed. B18: 94, 1976 (Not translated in Polymer Sci. U.S.S.R.) 2. N. M. BOL'BIT and S. Ya. FRENKEL, Vysokomol. soyed. A20: 294, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 2, 332, 1978) 3. Russian Authors' Cert. lifo. 525706; Byul. Izobret., No. 31, 1976 4. C. V. KOROLEV, Doklady I Vseoyuz. Konf. po khimii i fiziko-khimii polimerizatsionnosposobnykh oligomerov (Reports I. All-Union Conf. on the Chemistry and Physical Chemistry of Polymerizable Oligomers). Chernogolovka, 1977 5. S. Ya. FRENKEL, Vvedenie v statisticheskuyu teoriyu polimerizatsii (Introduction to the Statistical Theory of Polymerization). Ch. 6, Izd. "Nauka", 1965 6. D. OUDIAN, Osnovy khimii polimerov (The Fundamental Chemistry of Polymers). Ch. 4, Izd. "Mir", 1974 7. C. HAM, Sopolimcrizatsiya (Copolymerization) Ch. 14, Izd. "Khimiya", 1971 8. G. HAM, Sopolimerizatsiya (Copolymerization). Ch. I, Izd. "Khimiya", 1971 9. A. CHARLESBY, Yadernye izlucheniya i polimery (Nuclear Radiations and Polymers). 321, Izd. Inostr. Lit., 1962 10. A. CHAPIRO, Radiation Chemistry of Polymeric Systems. N.Y.-London, 120, 1962 11. R. HOUWlNK and A. STAVERMAN, Khimiya i tekhnologiya polimerov (Polymer Chemistry and Technology). v. 2, 317, Izd. "Khimiya", 1965 12. V. A. MYACCHENKOV and S. Ya. FRENKEL, Uspekhi khim. 37: 2247, 1968; 42: 827~ 1973; 47: 1261, 1978