Polymerization of acrylonitrile in the presence of lithium polystyryl

Polymerization of acrylonitrile in the presence of lithium polystyryl

POLYMERIZATION OF ACRYLONITRILE IN THE PRESENCE OF LITHIUM POLYSTYRYL* I. G. KI~AS~COSEn'SKAYA, E. S. GAlVKINA, B. G. BELEN'KII and B. L. YERUSALIMSKI...

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POLYMERIZATION OF ACRYLONITRILE IN THE PRESENCE OF LITHIUM POLYSTYRYL* I. G. KI~AS~COSEn'SKAYA, E. S. GAlVKINA, B. G. BELEN'KII and B. L. YERUSALIMSKII ttigh Polymers Institute, U.S.S.R. Academy of Sciences

(Received 31 May 1976)

Acrylonitrile (AN) polymerization is more efficiently initiated in toluene by lithium polystyryl (LPS) (up to 55%) than by lithium butyl (~ 1%). The styreneacrylonitrile block copolymers produced had 30-50 mole % of the AN chain units; the molecular weights were (4-5) x 104 for the styrene and (3-50) × 108 for the AN part.

ACRYLONITRILE (AN) polymerization over metal alkyls in non-polar media is known to give rise to a high polymer from only a small amount of the initiator [ 1-4]. The initiation efficiencyf is usually 1--7% in such systems. The main amount of the initiator is utilized in a production of inactive organometallic compounds as short chains (up to 100 AN units long)or as small rings [1, 5]. There appears to be a clash between the greater tendency of the short growing chains to become in~. ~t.ivated, and the higher stability of the high molecular weight (mohwt.) reac:ive centres. This can be basically attributed to disturbance of the homogeneity of the reaction mixture at an early stage and a consequent hindrance to inactivation of these, which consists of mono- or bimolecular reactions of the counter ion with the polar group of the growing chain [1, 6]. I t is likely however, that a similar effect in quality could be due to a reduction in the mobility of the growing chain as they become longer and that this happens regardless of the phase structure of the system. One could verify the last theory by assessing the value o f f during AN polymerization over a high mol.wt, initiator which is soluble in a hydrocarbon. We selected lithium polystyryl (LPS) as such an initiator. The value of f was found to be much larger under these conditions when compared with ini-~iation over the normal metal alkyls. It should be noted that polymerization of system AN-LPS was described in the literature [7-10] but t h a t the problem interesting us had not been tackled. The cited literature only suggest the possible synthesis of AN-styrene block copolymers. * Vysokomol. soyed. A19: No. 5, 999-1003, 1977. 1153

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EXPERIMENTAL

Earlier reports dealt with the purification of toluene, A N [2] and tetramethylethylenexiiamine [4]. Lithium butyl was produced from metallic lithium and butyl chloride in heptane solution. Styrene was purified by washing with a 5~o NaOH solution and was then dried over ~alcium chloride roasted with zeolite, calcium hydride and tributyl dimagnesium iodide. The polymerization were carried out in two stages in ampoules under vacuum. The first ~tage consisted of polymerizing the styrene, the second of cooling to the required temperature, 4~dding the AN and polymerizing the latter. The reaction mixture was decomposed with alcohol acidified with HCI, the polymerizates were washed with alcohol, and then vacuum ~dried at 40°C. The viscosity of the polystyrene (PS} was determined at 30°C in toluene, the mol.wt. ~alculated from formula [/~]=0.64 X 10 -4 M°'75 [11]. [~] for the block copolymer was determined in DMF at 25°C. That of P A N was found from the difference: [~]pAS=[~]B--[t/]pS, in which ~t/]B is intrinsic viscosity of the block copolymer, [t/]ps, that of the "live" PS determined at 25°C in DMF. The validity of this calculation comes from the additivity of the block copolymer properties when compared with those of PS and P A N [12] and was confirmed by experiment. The mol.w~, of the AN part of the block copolymcr was calculated by using the formula: [~/]pA~=2.33 X 10-~ M°'Ts [13]. Thin layer chromatography (TCL) was carried out on 6 X 9 cm slides covered with silica gel K S K [14]. The eluent used to estimate the mol.wt, was a cyclohexane-benzene-aeetone mixture using a components ratio of 12 : 4 : 0-7, while the block copolymer characteristics were measured in a ]:)MF-benzene mixture using various ratios. PS was deposited on the slides from CC14 solutions, the P A N and the block copolymer from those in DMF; ascending ~hromatography was used. The slides were sprayed with a 3~/o solution of KMnO~ in conc. H2SO4 to detect PS while heating at 140-150°C for 15 re_in. The spots of the polymers appeared black on the plate background of the slide. P A N was detected by spraying with a 10~o K O H ~solution and heating 10-15 min at 140-150°C. This coloured the P A N zones a pale orange. Narrow fractions of PS produced by the firm "Waters", USA, were used as reference stan~lards. RESULTS

Styrene polymerization. This m o n o m e r w a s p o l y m e r i z e d in t o l u e n e a t a [M]/ /[I] I> 100 ([M], [I] a r e c o n c e n t r a t i o n s o f m o n o m e r a n d i n i t i a t o r ) t o 1 0 0 % c o n v e r s i o n o v e r l i t h i u m b u t y l (Table 1). T h e i n i t i a t i o n w a s c o m p l e t e long before t h e e x h a u s t i o n o f t h e m o n o m e r u n d e r t h e s e l e c t e d c o n d i t i o n s [15]. T h e e x p e r i m e n t a l mol.wt. M e which was found in this way for PS was 5 times larger than the theor e t i c a l M t ( T a b l e 1, e x p . 1). A c c o r d i n g t o T L C t h i s p o l y m e r c o n t a i n e d s o m e q u a n t i t y o f low m o l . w t , c h a i n s in a d d i t i o n t o t h e m a i n f r a c t i o n w i t h M ~ 4 0 , 0 0 0 - 4 5 , 0 0 0 ( F i g . 1, p o i n t 5). I t w a s possible t o p r o d u c e a P S w i t h a n a r r o w M W D in a t w o s t a g e process, in w h i c h t h e first s t a g e c o n s i s t e d o f t h e f o r m a t i o n o f o l i g o - l i t h i u m s t y r y l a t a low [M]/[I] r a t i o (Table 1, t e s t 2). T h e m o l . w t , o f t h e P S w a s t h e n 1.5 t i m e s l a r g e r t h a n t h e t h e o r e t i c a l . T h e c h a r a c t e r i s t i c s o f this s a m p l e f r o m T L C s h o w e d t h a t o u r P S w a s v e r y similar t o t h e s t a n d a r d w i t h t h e n a r r o w M W D a n d h a r d l y c o n t a i n e d a n y low m o l . w t , f r a c t i o n (Fig. 1, p o i n t 4). Acrylonitrile polymerization. This p r o c e s s w a s c a r r i e d o u t o v e r L P S p r o d u c e d u n d e r t h e earlier c o n d i t i o n s (Table 2). T h e p r o c e s s w a s c o m p l e t e b e f o r e t h e m o n o m e r h a d b e e n f u l l y u t i l i z e d a n d t h e r e a s o n w a s t h e gelling o f t h e r e a c t i o n m i x t u r e .

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T h e A N conversion depends o n l y slightly on t e m p e r a t u r e as i n d i c a t e d by t h e f a c t t h a t r e d u c t i o n in t e m p e r a t u r e f r o m - - 2 5 t o --75°C, only slightly increased t h e mol.wt, o f the A N p a r t o f the block c o p o l y m e r (Table 2, tests 1,4 a n d 5).

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FzG. 1. TLC of PS in the system cyclohexane-benzene-acetone (12 : 4 : 0-7). 1-3-PS for M = 10,000, 33,000 and 510,000 respectively; 4--the PS from test 2, 5--the PS from test 1 (Table 1). T h e initiation efficiency was m u c h larger in all these cases (8-40%) t h a n w h e n lithium b u t y l was used (~-1%) [1]. Increase in f was also p r o d u c e d b y increasing A N c o n c e n t r a t i o n (Table 2, tests 1, 2) a n d in t h e presence o f a c o m p l e x i n g a g e n t (Table 2, t e s t 3). T h e r e was little effect o n t h e process b y a n y low mol.wt, f r a c t i o n p r e s e n t in t h e L P S (Table 2, tests 4 a n d 6). c

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FIG. 2. TLC of: 1--PS from test 1; 2--a block copolymer fraction (Table 2, test 4) in the system: a, b--12 : 4 : 0.7--eyelohexane : benzene : acetone, and of PAN (1), 2--fraction II of the block eopolymer (Table 2, test 4) in the systems: I-benzene; I I - - 1 : 1 benzene : DMF; I I I - - 7 : 3 benzene : DMF; IV--DMF. TLC development in c, d with: a--3~o H,SO4 solution; b-- 10% NaOH solution T h e a u t h o r s o f t h e earlier studies on f o r m a t i o n o f t h e block c o p o l y m e r [8, 10] h a d limited t h e i r s t a t e m e n t to t h e facts of its f o r m a t i o n w i t h o u t giving a n y o f its characteristics. One o f t h e samples (Table 2, t e s t 4) o b t a i n e d b y us was identified

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i n detail b y TLC. I t h a d b e e n first divided into a n acetone-soluble f r a c t i o n b y e x t r a c t i o n w i t h acetone, (40%) a n d c o n t a i n e d a b o u t 64 mole~/o of A N (Fraction I I ) . F r a c t i o n I was f o u n d b y T L C t o be a m i x t u r e o f t h e block c o p o l y m e r (with a larger s t y r e n e content) w i t h PS. T h e p a r t o f t h e sample remaining a t t h e s p o t t i n g p o i n t o f t h e T L C c o n t a i n e d P S (Fig. 2a) a n d P A N (Fig. 2b). T h e state o f conjugat i o n o f t h e P S a t t h e spotting p o i n t of the sample was indicated b y the fact t h a t t h e s t y r e n e h o m o p o l y m e r m o v e d in t h e centre o f the slide u n d e r these conditions (Fig. 1). F r a c t i o n I I showed t h a t trace a m o u n t s o f t h e s t y r e n e h o m o p o l y m e r are p r e s e n t (move w i t h the benzene front; Fig. 2~) a n d t h e block copolymer containing various A N quantities. T h e stepwise c h r o m a t o g r a p h y in benzene: D M F m i x t u r e s used in various proportions resulted in a f r a c t i o n a t i o n of t h e sample (Fig. 2c,

d). T h e use o f a n organometallic c o m p o u n d o f high mol.wt, as initiator of A N pol y m e r i z a t i o n t h u s g r e a t l y i m p r o v e d t h e initiation efficiency o v e r t h a t for b u t y l lithium. T h e f o r m a t i o n of a small n u m b e r o f chains w i t h a small c o n t e n t o f A N c h a i n units, which is t y p i c a l for A N p o l y m e r i z a t i o n in the presence o f organometallic initiators, occurs m u c h less in s y s t e m A N - L P S . Translated by K. A. ALLEN REFERENCES

1. B. L. YERUSALIMSgH and A. V. NOVOSELOVA, Faserforseh. trod Textfltechnik 26" 293, 1975 2. B. L. YERUSALIMSKH and I. G. KRASNOSEL'SKAYA, Makromol. Chemle 123: 80,' 1969 3. I. G. KRASNOSEL'SKAYA, B. L. YERUSALIMSKII and G. N. NOVINSKAYA, VysokomoI, soyed. A16: 1730, 1974 {Translated in Polymer Sei. U.S.S.R. 16: 8, 2002, 1974) 4. I. G. KRASNOSEL'SKAYA, V. M. DENISOV, B. L. YERUSALIM~KII and A. I. KOL'TSOV, Vysokomol. soyed. A17: 1098, 1975 (Translated in Polymer Sei. U.S.S.R. 17: 5, 1259, 1975) 5. I. G. KRASNOSEL'SKAYA and B. L. YERUSALIMSKII, Vysokomol. soyed. B 1 7 : 436,~ 1975 (Not translated in Polymer Sci. U.S.S.R.) 6. I. G. KRASNOSEL'SKAYA and B. L. YERUSALIMSKII, Vysokomol. soyed. A12: 2233, 1970 (Translated in Polymer Sei. U.S.S.R. 12: 10, 2532, 1970) 7. U.S. Pat. 3031432, 1962 8. R. C. JAIN, S. P. LUTHRA and R. T. THAMPI, Intemat. Syrup. Maeromolecules, Helsinki, vol. 2, 943, 1972 9. A. LANGER, Advances in Chemistry, Series 130, Am. Chem. Soc., Washington, 1974 10. R. B. SEYMOUR, D. R. OWEN and G. A. STAHL, Polymer Preprints 14: 658, 1973 11. R. FIGINI and G. V. SCHULZ, Z. phys. Chemie 23: 233, 1960 12. M. SHVITS, Anionnaya polimerizatsiya (Anionic Polymerization). Izd. "Mir", 89, 1971 13. R. CLELAND and W. STOCKMEYER, J. Polymer Sei. C17: 473, 1955 14. B. G. BELENKII and E. S. GANKINA, J. Chromatogr. 53: 3, 1970 15. H. L. HSIEH, J. Polymer Sci. A3: 163, ~!965