Polymerization of styrene by trichloroacetic acid and salts of variable-valency metals

Polymerization of styrene

931

18. J. H. HAY and M. SABIR, Polymer 10: 203, 1969 19. L. MANDELKERN, F. A. OlUNN and P. J. FLORY, J. Appl. Phys. 25: 840, 1954 20. A. GONTHIER, G. VII)OTTO and A. J. KOVACS, IUPAC International Symposium on Makromolecules, Leiden 2: 797, 1970 21. P. H. GEIL, Polimernye monokristally (Polymer Single Crystals). Izd. "Khimiya", 1968 (Russian translatior~) 22. J. P. ARLIE, P. SPEGT and A. SKOULIOS, Compt. rend. 261: 436, 1965 23. J. P. ARLIE, P. SPEGT and A. SKOULIOS, Makromolek. Chem. 104: 212, 1967 24. W. PECHOLD, Kolloid-Z. und Z. ftir Polymere 228: 1, 1968 25. L. MANDELKERN, J. G. FATOU and K. OHN0, J. Polymer Sei. B6: 615, 1968 26. J. D. HOFFMAN, SPE Trans. 4: 315, 1964 27. J. D. HOFFMAN, J. J. LAURITZEN, Jr., E. PASSAGHA, G. C. ROSS, L. J. FROLEN and J. J. WEEKS, Kolloid-Z. und Z. fiir Polymere 231: 564, 1969 28. M. L. WILLIAMS, R. F. LANDEL and J. D. FERRY, J. Amer. Chem. Soe. 77: 3701, 1955 29. G. VIDOTTO, D. LEVY and A. J. KOVACS, Kolloid-Z. und Z. f'tir Polymere 230: 289, 1969 30. Yu. K. GODOVSKII and G. L. SLONIMSKII, Vysokomol. soyed. All: 1285, 1969 (Translated in Pol)nner Sci. U.S.S.R. 11: 6, 1461, 1969) 31. R. L. CORMIA, F. P. PRICE and D. J. TURNBUI~, J. Chem. Phys. 37: 1333, 1962 32. D. J. TURNBULL, J. Phys. Chem. 66: 609, 1962

POLYMERIZATION OF STYRENE BY TRICHLOROACETIC ACID AND SALTS OF VARIABLE-VALENCY METALS* YE. M. DUKHNENKO, T. V. TAVOLOZHANSKAYA a n d V. V. SILANT'EV Krasnodar Polytechnic Institute (Received l I June 1971)

IN CATIONIC p o l y m e r i z a t i o n , b o t h t h e r a t e a n d also t h e degree of p o l y m e r i z a t i o n are d e t e r m i n e d to a considerable e x t e n t b y t h e conditions u n d e r which t h e p r o c ess is carried o u t a n d t h e p o l a r i t y of t h e m e d i u m . T h e effect of t e m p e r a t u r e , t h e p o l a r i t y of t h e m e d i u m a n d also its s o l v a t i n g c a p a c i t y , on t h e m o l e c u l a r weight a n d yield of t h e p o l y m e r f o r m e d for p o l y m e r i z a t i o n in t h e presence of p r o t o n i c acids h a v e b e e n discussed [1-3]. One of t h e possible m e t h o d s of increasing t h e r a t e a n d degree o f p o l y m e r i z a t i o n is to stabilize a c t i v e sites b y t h e i n t r o d u c t i o n of special additions into t h e r e a c t i o n m e d i u m . S t r o n g c o m p l e x i n g agents could be used, for e x a m p l e , as a d d i t i o n of this t y p e . R e p o r t s h a v e a p p e a r e d in r e c e n t y e a r s dealing w i t h c a t a l y t i c s y s t e m s consisting of p r o t o n i c acids a n d m e t a l salts, acids a n d m e t a l s a n d t h e i r d e r i v a t i v e s

[4-s]. * Vysokomol. soyed. AI5: No. 4, 828-831, 1973.

932

Y~.. M. DuxIrrr~rKo et aS.

T h e potentialities o f c a t a l y t i c s y s t e m s o f this t y p e n e c e s s i t a t e a detailed s t u d y o f t h e kinetic f e a t u r e s o f t h e f o r m a t i o n o f p o l y s t y r e n e u n d e r t h e effect o f trichloroacetic acid (TCA) in t h e presence o f additions o f m e t a l s salts. W e h a v e s t u d i e d t h e p o l y m e r i z a t i o n o f s t y r e n e in d i c h l o r o e t h a n e (DCE) a n d n i t r o m e t h a n e (NM) in t h e presence of Mn(OCOC~I3)2, Cr(OCOCHs) s, Ni(OCOCHa)2 a n d Bi(OCOCH3)~. T h e s e salts were selected because o f t h e i r c o m p l e t e solubility in t h e r e a c t i o n m i x t u r e , w h i c h m a d e it possible t o c a r r y o u t t h e process h o m o g e n e o u s l y , a n d b e c a u s e of t h e i r solubility in t h e n o n - s o l v e n t for t h e p o l y m e r , w h i c h m a d e it possible to r e m o v e t h e salt f r o m t h e p o l y m e r readily. EXPERIMENTAL The styrene and ethylbenzene were purified, dried and distilled by the methods given in [1]. They had the following characteristics; styrene: n~5, 1.5439, purity, 99-8~, water content, 0"008~o; ethylbenzene: n~°, 1.4959, water content, 0.011 ~ . Before being used, NM was dried with CaCl~ and distilled twice to remove traces of water and the fraction boiling at 101°C was selected; n~°, 1.3819. Water content (Fischer's method), 0.027 Yo. DCE was purified and distilled as in [9]. The fraction boiling at 83"4-83.5°C was selectod; n~°, 1.4472. The water content did not exceed 0"015~o. The chemical purity grade TCA was dried in vacuum and stored over CaCI~ in a vacuum dessieator. The acid used had an acid number of 342-344 mg of KOH (theoretical acid number, 343 mg of KOH), d ° 1.649; d~° 1.638; d~ 1.632. The water content in the acid was up to 0.1 ~o. Mn(OCOCH3)~, Ni(OCOCH3)2, Cr(OCOCHs)3, Bi(OCOCHs)s were used as chemical grade materials and were dried in vacuum at 100-110°C before use. The kinetics of polymerization were studied by dilatometry [2]. Specimens of the reaction mixture were titrated during the polymerization in order to determine the catalyst consumption. The specimens were taken with a micropippette with an accuracy of 4-0.01 ml, diluted with 20 ml of benzene and titrated against 0.01 N alcoholic solution of K O H in the presence of phenolphthalein. The polymer was precipitated with ethanol. The polymer was freed from catalyst by repreeipitation from toluene into ethanol and was then dried at 25°C. The polymers' molecular weights were determined by viscometry in toluene at 25°C from the equation [t/]~ 1.7 × l0 -4 M °'~' [I0]. RESULTS AND DISCUSSION F i g u r e l a shows curves for t h e effect o f additions of salts of v a r i o u s m e t a l s on t h e p o l y m e r yield a t 30°C. I t m a y b e seen t h a t t h e r a t e of p o l y m e r i z a t i o n increases c o n s i d e r a b l y n o t o n l y w i t h a n increase in t h e p o l a r i t y o f t h e m e d i u m b u t especially w h e n small additions of Mn 2+, Bi 2+ or Ni ~+ salts are i n t r o d u c e d i n t o t h e s y s t e m . I t s h o u l d be n o t e d t h a t , s t a r t i n g f r o m c e r t a i n salt c o n c e n t r a t i o n s ( a p p r o x i m a t e l y 0.015 g.mole/1.), a f u r t h e r increase o f it in t h e s y s t e m does n o t cause a n y acceleration b u t r a t h e r begins to inhibit p o l y m e r i z a t i o n (Fig. lb). T h e kinetic order o f t h e r e a c t i o n w i t h r e s p e c t to the acid was d e t e r m i n e d f r o m t h e dep e n d e n c e of t h e p o l y s t y r e n e yield on t i m e as t h e T C A c o n c e n t r a t i o n was c h a n g e d f r o m 1.9 to 2-7 g. mole/1. F i g u r e lc shows the corresponding curves o b t a i n e d a t 30°C for t h e p o l y m e r i z a t i o n of s t y r e n e in D C E , which is quite a p o l a r solvent. I t m a y be seen t h a t t h e p o l y m e r i z a t i o n r a t e increases as t h e TCA c o n c e n t r a t i o n

Polymerization of styrene

933

is increased. From the logarithmic relationship between the initial polymerization rate and the acid concentration, the order of the reaction with respect to the acid was found to be equal to 2.0. The concentrations of the remaining components was held constant by the addition of appropriate quantities of ethyl benzene whose dielectric permeability approximates to the dielectric permeability of styrene. The order of the reaction with respect to the monom er was equal to 1.8 /

5

2O

2

g o

0

~v"~ ZO

I 40

I ~0

I 80

T/me, mz'n

I /00

/

II /200

I 002

1 I 00,/ 00£

O, mole/L

g O

I 40

I ~0

[ 120

I f /6"0 2 0 0

77rne ~ rn/n

FIG. 1. Dependence of the yield of polystyrene at 30°C on (a, c) time, and (b) salt concentration, after 150 rain; [M]~5.85 mole/1. (a, b), 4.3 mole/1. (v); a - - l - 3 - - i n a DCE medium at [DCE] ~ 3.94 and [TCA]--~2.1 mole/1.; 4 - 7 -- in an NM medium at [NM]= 4.2 and [TCA]----1.12 mole/1.; 8--as 4 - 7 but [TCA]~2.53 mole/1. 1, 4 and 8 without salt addihons; 2--with Cr(OCOCHs)a; 3, 7-- Mn (OCOCHa)z;5-- Ni (OCOCI-Ia)2; 6-- Bi (OCOCHa)~;salt concentrations: 2, 3--0.08; 5-7--0.012 mole/1, b-- in NM with addition of Ni(OCOCH3)2 at [TCA]~-l.38 mole/1. (•); in DCE with addition of Mn(OCOCHs)2 at [TCA]=2-1 mole/1. (2), c--[DCE] : 4 . 0 mole/1, with the following values of [TCA]: 1--1.93, 2--2.26, 3--2.50, 4--2-70 mole/1. The second order reaction with respect to the acid, rather t h a n the very much higher order frequently found, points to the fact t h a t not all the acid molecules participate in the formation of active sites, since only the monomeric form of the acid is catalytically active [11]. In order to find the order of reaction with respect to the acid more accurately, titration of specimens of the reaction mixture was carried out during the reaction. The titration data are shown in Fig. 2. The acid participates in two elementary acts, initiation and chain termination. The amount of acid used up eharacterizes the active portion of the acid t h a t participates in the initiation stage. I n Fig. 2 it m a y be seen t h a t the consumption of the acid, and consequently the concentration of active sites as well, increases as the initial TCA concentration is increased. The kinetic order of the polymerization reaction with respect to TCA is equal to unity. Consequently, in the present case only one of the two acid molecules t h a t participate in the formation of the active site initiates the chain, and the other evidently solvates the ion pair, since the acid is considerably more polar t h a n the other components of the reaction mixture. When cocatalyst additions are introduced into the reaction system, the

@34

Y~. M. DU~T~.~TXO et al.

order of the reaction with respect to the acid decreases and becomes equal to 1.4, the reaction rate and polymer yield thus increasing (Fig. la). In this w a y the use o f salts makes it possible to reduce the initial acid concentration b y a factor of more than 2 whilst achieving the same polymerization rate (Fig. la, curves 7 and 8). In order to explain how the salt accelerates the polymeization process, 3

~, 2

I.j

I

1o

JO

30 7~ne, rn+~

FTG. 2. Change in the TCA concentration during polymerization at 30°C for [DCE] =4.0 and [M]=4.3 mole/1. Values of [TCA]: 1--2.26; 2--2.50; 3--2.70 mole/1. we assume that a donor-accepter interaction is possible between an acid anion and the metal of the salt. The creation of such a coordination bond, although weak, removes the acid anion from the sphere of interaction with the cation, and this clearly leads to a shift in the dissociation equilibrium of the acid in the direction o f the formation of ion pairs O...HO

R--C

/J

\

\

//

C--R

~

2RC00H

~

(RC00Hs+RC00

-)

OH...O

Thus the effect of the salt at concentrations not greater than 0.015 mole/1. •clearly reduces principally to an increase in the ionization of the acid. The order of the reaction with respect to the salt is 0.6 (for salt concentrations in the range 0.003-0.01 mole/1.). The kinetic equations obtained m a y be written in the following way ([M] is the monomer concentration): V ~---k [C] 1"9 [ ~ ] 1 " 8 - -

without coeatalyst

v~-/¢ Iv]1"° [M] l's (taking account of only the active portion of the acid) v - ~ k [c]1"4[M]2"° [Mn] °'~ with cocatalyst

(1) (2) (3)

The way in which the polystyrene yield with time depended on the concentrations of the catalyst, monomer and manganese acetate at 30, 0 and --20°C in ~TM was determined: treatment of the results obtained, as described above, makes it possible to write the kinetic equations for the reaction without cocatalyst v----/c [c]2"8[M] ~'° (at 30 °)

(4)

v = k [c] ~'4 [M] 8"~ (at 0 °)

(5)

v = k [c] ~'° [M] +~ (at

- - 2 0 °)

(6)

Polymerization of styrene

935.

and in the presence of the eoeatalyst v = k [el 2'~ [M] 3'° [Mn] °'5 (at 30 °) v-~k [c]2"° [M]4'3 [Mn] °'5 (at 0 °) v = k [el l"s [M]5"° [Mn] °'5 (at --20 °)

(7) (s) (9)

When nickel acetate is used as cocatalyst, the kinetic equation for the reaction at 30°C in a medium of NM is similar to equation (7). In the equations presented, it should be noted that the orders of the reaction with respect to the monomer and acid are higher in absolute magnitude than those for polymerization in DCE. In this case, as in those described previously [2], a specific effect of NM is apparent, which is capable of participating in a donoracceptor interaction with the components of the system. The gross rate constants (k x 107) for the polymerization of styrene in the presence of TCA without salt are equal to 31.6, 2-24 and 0.355 1./mole-l.sec -1 a t 30, 0 and --20°C respectively, and in the presence of Mn(OCOCHa)~, 63.0, 7.95 and 1.58 1./mole-l.sec -1 at the same temperatures. The activation energy, E, for the polymerization of styrene without salt additions, calculated from t h e experimental data, is 13.7:~0.1 kcal/mole. The introduction of Mn(OCOCH3)~ into the system reduces the activation energy to 10.9-4-0.1 keal/mole. This is evidently connected with a decrease in Ein and an increase in E t because of the donor-aceeptor interaction of the variable-valency metal with the acid anion. T h e latter, on the one hand, favours the ionization of the acid, and consequently is conducive to a decrease in Ein, b u t on the other hand, it favours stabilization o f the acid anion that causes chain termination and thus E t is increased. The resulting activation energy is reduced, since

E=Ein+Ep--Et. The w a y in which the polystyrene's molecular weight depends on the composition of the reaction mixture (polymerization a t - - 2 0 ° C in NM with [TCA]: ----1.38 mole/1.) is shown below [Mn (OCOCI-Is)~]X 10-a, mole/l. 0.20 0.50 1.50 1-80 2.60 - -2 323 357 542 529 310250

M×IO

It m a y be seen that small additions of the salt considerably increase the poly: styrene's molecular weight. However, a further increase in the salt concentration leads to a reduction in molecular weight which is evidently connected with an increase in the number of active sites because of the rise in the degree of ionization of the acid. CONCLUSIONS

The polymerization of styrene in the presence of triehloroacetie acid and Mn ~+, Ni ~+, Bi 2+ and Cr 3+ acetates has been studied. It is suggested on the basis of the experimental data that the use of variable-

936

K . A . ANDRIANOV e$ al.

v a l e n c y m e t a l salts as c o c a t a l y s t s is c o n d u c i v e to ionization of t h e acid a n d s t a b i l i z a t i o n o f t h e c h a i n - t e r m i n a t i n g acid anion: b e c a u s e of this, t h e r e a c t i o n r a t e :and t h e m o l e c u l a r weight of t h e p o l y s t y r e n e increase. Translated by G. F. MODY~N REFERENCES

l. A. F. NIKOLAYEV, K. V. BELOGORODSKAYA and Ye. M. BABUSHKINA, Zh. prikL khimii 41: 1865, 1968 2. A. F. NIKOLAYEV, K. V. BELOGORODSKAYA and Ye. M. BABUSHKINA, Vysokomol. soyed. A1O: 1861, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 8, 2158, 1968) 3. A. F. NIKOLAYEV, K. V. BELOGORODSKAYA, Ye. M. DUKHNENKO, A. V. POPOVA and A. F. KARAKASH, Vysokomol. soyed. B12: 24, 1970 (l~Tot translated in Polymer Sci. U.S.S.R.) 4. S. O ~ A , T. HIGASHIMYRA and T. WATANABE, Makromolek. Chem. 50: 137, 1961 5. NORO KEN and TAKITA KHIROSI, Japanese Pat. 19344, 1964 6. M. F. SHOSTAKOVSKH, A. M. KHOMUTOV and A. P. ALIMOV, Izv. AN SSSR, seriya khimieh., 1848, 1964 7. V. A. PONOMARENKO and N. N. KHOMUTOVA, Izv. AN SSSR, seriya khimich., 1153, 1969 8. F. DAWANS and Ph. TEYSSIE, J. Polymer Sci. B7: 111, 1969 9. A. WEISSBERGER and E. PROSKAUER, Organicheskiye rastvoriteli (Organic Solvents). p. 396, Izd. inostr, lit., 1958 (Russian translation) 10. S. R. RAFIKOV, S. A. PAVLOVA and N. I. TVERDOKHLEBOV, Metody opredeleniya molekulyarnykh vesov i polidispersnosti vysokomolckulyarnykh soyedinenii (Methods of Determining Molecular Weights and Polydispersity of Polymers). p. 325, Izd. AN SSSR, 1963 11. I. V. BEREZIN, K. VATSEK and N. F. KAZANSKAYA, Dokl. AN SSSR 144: 139, 162

THERM0-0X1DATIVE DEGRADATION OF POLYSPIRODIMETHYLTITANOSILOXANES* K . A. AI~DRIAI~OV, ~T. A. KURASHEVA, L. I. KUTEINIKOVA a n d I. V. ZHURAVLEVA Institute for Elemento-organic Compounds, U.S.S.R. Academy of Sciences (Received 16 June 1971)

THE r e a c t i o n for t h e synthesis o f p o l y s p i r o d i m e t h y l t i t a n o s i l o x a n e s h a s b e e n d e s c r i b e d p r e v i o u s l y [1]. T h e b e h a v i o u r o f these p o l y m e r s during t h e r m o - o x i d a r i v e d e g r a d a t i o n is o f interest because o f t h e i r u n u s u a l m a c r o m o l e c u l a r s t r u c t u r e . I t w a s to b e e x p e c t e d t h a t , in a d d i t i o n to t h e t h e r m o - o x i d a t i v e d e g r a d a t i o n o f * Vysokomol. soyed. A15: No. 4, 832-835, 1973.