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The Influence of Aromatic Ethers on the Association of the Polystyryllithium and 1,1-Diphenylmethyllithium Active Centers in Benzene L E W I S J. F E T T E R S Institute of Polymer Science, The University of Akron, Akron, OH 44325 RONALD
N. YOUNG
Department of Chemistry, The University of Sheffield, Sheffield S3 7 H F ,
U.K.
The influence of diphenyl ether and anisole on the association of the polystyryllithium and 1,1-diphenylmethyllithium active centers has been measured. Severe disaggregation of the polystyryllithium dimers, present i n pure benzene, was found to occur at levels of ether addition at which several r e l i a b l e kinetic studies reported i n the l i t e r a t u r e unequivocally demonstrate a 1/2 order dependence upon polystyryllithium. These results indicate that a necessary connection between the degree of aggregation of organolithium polymers and the observed kinetic order of the propagation reaction need not exist. The a c t i v e c e n t e r s o f the p o l y d i e n y l - and p o l y s t y r y l l i t h i u m s p e c i e s , which can be c h a r a c t e r i z e d as having p o l a r i z e d covalent carbon l i t h i u m bonds, appear (1-8) t o form dimeric aggregates i n hydrocarbon s o l v e n t s a t c o n c e n t r a t i o n s (,10) t o e x h i b i t a 1/2 o r d e r d e p e n d e n c y on polystyryllithium concentration. Hence, the c o n c e p t t h a t o n l y t h e u n a s s o c i a t e d c h a i n e n d s a r e r e a c t i v e may be v a l i d f o r t h i s s y s t e m s i n c e a s s o c i a t i o n s t u d i e s h a v e shown (^,2^,^7,8^) t h a t t h e p o l y s t y r y l l i t h i u m c h a i n ends a r e a s s o c i a t e d as d i m e r s . (Szwarc h a s s t a t e d (11) t h a t p o l y s t y r y l l i t h i u m i s " p r o b a b l y t e t r a m e r i c i n cyclohexane." T h i s assessment, though, f a i l e d t o c o n s i d e r the l i g h t s c a t t e r i n g r e s u l t s (]_,8) o f J o h n s o n and W o r s f o l d ) . S e v e r a l s t u d i e s h a v e a p p e a r e d UJi/J^/14.) i w h i c h t h e p r o p a g a t i o n r e a c t i o n s i n v o l v i n g s t y r y l l i t h i u m were examined i n m i x e d s o l v e n t s y s t e m s c o m p r i s i n g b e n z e n e o r t o l u e n e and e t h e r s . The k i n e t i c s were examined under c o n d i t i o n s where the e t h e r c o n c e n t r a t i o n was h e l d c o n s t a n t and t h e a c t i v e c e n t e r c o n c e n t r a t i o n varied. I n most c a s e s , t h e k i n e t i c o r d e r s o f t h e r e a c t i o n s were i d e n t i c a l t o those observed i n the absence of the e t h e r . Thus, i n p a r t , t h e c o n c l u s i o n was r e a c h e d (13,14) t h a t t h e e t h e r s d i d not a l t e r the d i m e r i c a s s o c i a t i o n s t a t e of p o l y s t y r y l l i t h i u m . The e t h e r s u s e d w e r e t e t r a h y d r o f u r a n , d i p h e n y l e t h e r , a n i s o l e , and t h e o r t h o and p a r a i s o m e r s o f e t h y l a n i s o l e . We h a v e e x a m i n e d t h e i n f l u e n c e o f d i p h e n y l e t h e r and a n i s o l e on t h e a s s o c i a t i o n o f t h e p o l y s t y r y l l i t h i u m and t h e 1,1-diphenylm e t h y l l i t h i u m a c t i v e c e n t e r s i n b e n z e n e s o l u t i o n . The a n a l y t i c a l t o o l u s e d was t h e vacuum v i s c o m e t r y method U,_2,^3,j>) w h i c h u t i l i z e s c o n c e n t r a t e d s o l u t i o n s o f p o l y s t y r y l l i t h i u m and t h e t e r m i n a t e d p o l y m e r i n t h e e n t a n g l e m e n t r e g i m e . Our r e s u l t s show t h a t the p r e s e n c e of t h e s e e t h e r s can a l t e r the a s s o c i a t i o n s t a t e s of the f o r e g o i n g a c t i v e c e n t e r s . These f i n d i n g s p a r a l l e l p r e v i o u s work (_2) i n v o l v i n g t e t r a h y d r o f u r a n . Experimental Section The p r o c e d u r e s u s e d f o r s t y r e n e and b e n z e n e p u r i f i c a t i o n a r e g i v e n e l s e w h e r e (15) a s i s t h e t e c h n i q u e u s e d t o s t u d y t h e a s s o c i ation states · The v i s c o m e t r i c method r e l i e s on t h e f a c t t h a t i n the entanglement r e g i o n , non-polar polymers i n s o l u t i o n and t h e m e l t e x h i b i t N e w t o n i a n v i s c o s i t i e s w h i c h a r e d e p e n d e n t on
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n
—
3 · U
—
M . A c o m p i l a t i o n o f n-M d a t a p r e s e n t e d e l s e w h e r e (16) r e v e a l s t h a t f o r near-monodisperse polymers, the predominant v a l u e o f t h e e x p o n e n t i s 3.4. F u r t h e r m o r e , D o i (17) h a s r e c e n t l y e x t e n d e d de Gennes (18) t u b e m o d e l and h a s shown (17) t h a t n M^, * *. The v a l u e o f t h e e x p o n e n t means t h a t e v e n s m a l l c h a n g e s i n a s s o c i a t i o n s t a t e s can be, i n p r i n c i p l e , measured w i t h a h i g h degree o f accuracy. The c o n c e n t r a t e d s o l u t i o n v i s c o s i t y m e a s u r e m e n t s w e r e done a t 20°C a s w e r e t h e p o l y m e r i z a t i o n s . The m o l e c u l a r w e i g h t s ( M ^ o f t h e b a s e p o l y s t y r e n e s u s e d i n t h i s w o r k r a n g e d f r o m 1.2x 10 to 1.7xl0 ( b a s e d on GPC m e a s u r e m e n t s ) w h i l e t h e c o r r e s p o n d i n g p o l y m e r c o n c e n t r a t i o n s r a n g e d f r o m ca. 42 t o 30 p e r c e n t . The i n i t i a t o r was p u r i f i e d , by d i s t i l l a t i o n ( 1 9 ) , s e c - b u t y l lithium (Lithco). The e t h e r s and 1 , 1 - d i p h e n y l e t h y l e n e were p u r i f i e d by s e q u e n t i a l e x p o s u r e t o CaH2, d i b u t y l magnesium ( L i t h c o ) w
w
Œ
5
5
In Anionic Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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and p o l y s t y r y l l i t h i u m . T h i s p u r i f i c a t i o n r o u t i n e t o o k a b o u t one week t o c o m p l e t e . GC a n a l y s i s , a f t e r p u r i f i c a t i o n , f a i l e d t o r e v e a l i m p u r i t i e s i n t h e s e compounds. The p o l y m e r i z a t i o n s w e r e conducted i n the presence o f the e t h e r s w i t h benzene a s the s o l vent. The p o l y s t y r y l l i t h i u m a c t i v e c e n t e r was c o n v e r t e d t o t h e 1,1-diphenylmethy1lithium c h a i n e n d b y t h e a d d i t i o n o f c a . 0.1 ml o f 1 , 1 - d i p h e n y l e t h y l e n e . The GPC a n a l y s i s w a s c o n d u c t e d u s i n g a s e v e n c o l u m n S t y r a g e l arrangement w i t h t e t r a h y d r o f u r a n a s the c a r r i e r s o l v e n t . Solu t i o n c o n c e n t r a t i o n s o f 1/8% (w/v) w e r e u s e d . The f l o w r a t e was 1 ml m i n . The c h a r a c t e r i s t i c s o f t h i s c o l u m n a r r a n g e m e n t a r e p r e s e n t e d elsewhere (20,21). The S t y r a g e l c o l u m n s w e r e c a l i brated using eleven polystyrene standards. A l l o f the p o l y s t y r e n e s p r e p a r e d i n t h i s work were a n a l y z e d by g e l p e r m e a t i o n chromatography._ W i t h o u t e x c e p t i o n , a l l c a m p l e s were f o u n d t o h a v e v a l u e s o f M / M ^ 1 . 0 7 a n d v a l u e s o f M /M 1 cm) t u b i n g . H a d j i c h r i s t i d i s a n d R o o v e r s (50) u s e d U b b e l o h d e v i s c o m e t e r s t o study c o n c e n t r a t e d p o l y i s o p r e n e s o l u t i o n s and concluded t h a t i n p r a c t i c e t h e technique i s l i m i t e d t o systems having v i s c o s i t i e s l e s s than 1 0 p o i s e . ( U n l e s s t h e s o l u t i o n s a r e d r i v e n by an i n e r t g a s ) . Our e x p e r i e n c e i s e n t i r e l y i n c o n c o r d a n c e w i t h t h i s assessment, as i s t h a t o f others (51). 3
5
1
3
s
3
F i n a l l y , two comments made (46) i n r e f e r e n c e t o o u r p r e l i m s t a t e m e n t (47) s h o u l d b e a s s e s s e d : (a) " P u r i f i e d , a n d n o t c o m m e r c i a l , e t h e r h a s t o be u s e d , o t h e r w i s e some c a r b a n i o n s a r e d e s t r o y e d . " Our p u r i f i c a t i o n p r o cedure i s presented i n the experimental s e c t i o n o f t h i s paper. The i m p l i c a t i o n t h a t we w o u l d u s e an u n p u r i f i e d e t h e r i s a n u n c a l l e d f o r i n v e n t i o n o f t h e a u t h o r s o f r e f . 46. inary
In Anionic Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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(b) "Prolong (sic) a c t i o n o f the ether g r a d u a l l y destroys the carbanions a srevealed by t h e decrease o f o p t i c a l a b s o r p t i o n a t 344 nm." We w i s h t o n o t e t h a t t h i s t e r m i n a t i o n r e a c t i o n seems n o t t o h a v e i n f l u e n c e d t h e v i s c o s i t y r e s u l t s o f Wang a n d S z w a r c (46) n o r t h o s e o f Y a m a g i s h i a n d c o - w o r k e r s (14) w h e r e s p e c i e s analogous t o d i p h e n y l e t h e r were used. T h e s e a u t h o r s (46) seem, though, t o imply t h a t t e r m i n a t i o n has i n f l u e n c e d o u r r e s u l t s r e g a r d i n g d i p h e n y l e t h e r . We h a v e , a s n o t e d , c o n s i d e r e d t h i s p o s s i b i l i t y i n o u r work. I n summary, we w i s h t o s u g g e s t t h a t i n t h e c a s e o f t h e t e t r a hydrof uran and aromatic e t h e r m o d i f i e d systems based o n s t y r e n e s t u d i e d t o d a t e , t h e r e does n o t appear t o e x i s t a d i r e c t r e l a t i o n s h i p b e t w e e n t h e mean-degree o f a c t i v e c e n t e r a s s o c i a t i o n a n d k i n e t i c order. We d o n o t mean, w i t h t h i s a s s e s s m e n t , t o i m p l y o r c l a i m t h a t t h e concept t h a t o n l y t h e unassociated a c t i v e c e n t e r s of p o l y s t y r y l l i t h i u m i n hydrocarbon s o l v e n t s a r e t h e a c t i v e en t i t i e s i sincorrect. However, o u r a s s o c i a t i o n r e s u l t s ( t h i s w o r k and r e f . 2), c o m b i n e d w i t h t h e a v a i l a b l e k i n e t i c f i n d i n g s f o r these ether m o d i f i e d p o l y m e r i z a t i o n s , seemingly i n d i c a t e t h a t r e a c t i o n o r d e r s need n o t n e c e s s a r i l y y i e l d d i r e c t i n s i g h t i n t o t h e states of active center association. In our opinion, greater u n d e r s t a n d i n g o f t h e apparent complex n a t u r e o f these o r g a n o l i t h i u m b a s e d r e a c t i o n s w i l l b e f o r t h c o m i n g b y a more j u d i c i o u s approach t o t h e i d e n t i f i c a t i o n o f t h e a c t i v e c e n t e r s i n these p o l y m e r i z a t i o n s ; a n d a p p r o a c h , w h i c h i n e f f e c t , was a d v a n c e d b y Brown some y e a r s a g o ( 5 2 , 5 3 ) . Along t h i s l i n e , Kaspar and T r e k o v a l (_54,_55) h a v e c o n c l u d e d f r o m t h e i r k i n e t i c a n a l y s i s t h a t styrene can r e a c t d i r e c t l y w i t h the p o l y s t y r y l l i t h i u m dimer i n benzene s o l u t i o n . A c k n o w l e d g e m e n t : We w i s h t o t h a n k P r o f . G. B e r r y , P r o f . J . D. F e r r y , P r o f . W. W. G r a e s s l e y , P r o f . N. H a d j i c h r i s t i d i s , D r . D. Pearson and P r o f . J . Schrag f o r t h e i r a d v i c e r e g a r d i n g t h e p r a c t i c a l l i m i t a t i o n s o f Ubbelhode v i s c o m e t e r s f o r t h e measure ment o f c o n c e n t r a t e d p o l y m e r s o l u t i o n s . We a l s o w i s h t o t h a n k D r . R. Q u i r k f o r h i s comments a n d i n f o r m a t i o n . References: 1. 2. 3. 4. 5. 6. 7.
Morton, M., Fetters, L. J . J . Polym. S c i . , (1964), 2 Part A, 3311. Morton, M.; Fetters, L. J . ; Pett, R.; Meier, J . F. Macromolecules, (1970), 3, 327. Fetters, L. J . ; Morton, M. Macromolecules (1974), 7, 552. Glaze, W. H.; Hanicak, J . E.; Moore, M. L.; Chandhuri, J . J. Organomet. Chem. (1972), 44, 39. Al-Jarrah, M. M.; Young, R. N. Polymer (1980), 21, 119. Hernandez, Α.; Semel, J . ; Broecker, H. C.; Zachmann, H. G.; Sinn, H. Makromol. Chem., Rapid Comm., (1980), 1, 75. Worsfold, D. J . J . Polym. S c i . , (1967), 5 Part A-1, 2783.
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8. Johnson, A. F.; Worsfold, D. J. J . Polym. Sci., (1965), 3 Part A-1, 449. 9. Worsfold, D. J.; Bywater, S. Can. J. Chem., (1964), 42, 2884. 10. Worsfold, D. J.; Bywater, S. Can. J. Chem., (1960), 38, 1891. 11. Szwarc, M. Science, (1970), 170, 30. 12. Worsfold, D. J.; Bywater, S. Can. J. Chem., (1962), 40, 1564. 13. Geerts, J.; Van Beylen, M.; Smets, G. J. Polym. S c i . , (1969), 7 Part A-1, 2805. 14. Yamagishi, Α.; Szwarc, M.; Tung, L.; Lo, G.-Y.S. Macromolecules (1978), 11, 607. 15. Morton, M.; Fetters, L. J . Rubber Revs., (1975), 48, 359. 16. Fetters, L. J.,; Morton, M. J. Polym. Sci., Polym. Lett. Ed. (1981), 19, i n press. 17. Doi, M. Polym. Prepr., Polym. Chem. Div., Am. Chem. Soc., (1981), 22 (1), 100. 18. de Gennes, P. G. J . Chem. Phys., (1971), 55, 572. 19. Worsfold, D. J.; Bywater, S. J. Organomet. Chem. (1967), 10, 1. 20. McCrackin, F. L. J . Appl. Polym. S c i . , (1977), 21, 191. 21. Ambler, M.; Fetters, L. J.; Kesten, Y. J. Appl. Polym. Sci., (1977), 21, 2439. 22. Robertson, R. E.; Marion, L. Can. J . Res., (1948), 26B, 657. 23. Bower, F. M.; McCormick, H. W. J. Polym. Sci., (1963), 1 Part A, 1749. 24. Brooks, B. W. Chem. Commun., (1967), 68. 25. Krume, S. Makromol. Chem., (1966), 98, 120. 26. Krume, S.; Takahashi, Α.; Nishikawa, G.; Hatana, M.; Kambara, S. Makromol. Chem., (1965), 84, 137, 147; i b i d . , (1966) 98, 109. 27. Gatzke, A. J . Polym. Sci., (1969), 7 Part A - 1 , 2281. 28. Aukett, P.; Luxton, A. R. J . O i l Colour Chem. Assoc., (1977), 60, 173. 29. Cotton, J . P.; Decker, D.; Benoit, H.; Farnoux, Β.; Higgins, J.; Jannik, G.; Ober, R.; Picot, C.; dos Claizeaux, J . Macromolecules (1974), 7, 863. 30. Gilman, H.; Gaj, B. J. J. Org. Chem., (1963), 28, 1725. 31. Cubbon, R. C. P.; Margerison, D. Proc. Roy. Soc., (1962), 268A, 260. 32. Waack, R.; McKeever, L. D.; Doran, M. A. Chem. Commun., (1969), 117. 33. Bywater, S.; Worsfold, D. J . J . Organomet. Chem., (1971), 33, 273. 34. Morton, M.; McGrath, J . E.; Juliano, P. C. J . Polym. Sci., (1969), No. 26 Part C, 99. 35. Fetters, L. J.; Morton, M. Macromolecules, (1969), 2, 453. 36. Morton, M.; Fetters, L. J.; Inomata, J.; Rubio, D.; Young, R. N. Rubber Chem. Tech., (1976), 49, 303. 37. Journe, J.; Widmaier, J . M. Eur. Polym. J . (1977), 13, 379. 38. Shirley, D. Α.; Johnson, J . R.; Hendrix, J . P. J. Organomet. Chem. (1968), 11, 209.
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Shirley, D. Α.; Hendrix, J . P. J . Organomet. Chem., (1968), 11, 217. Fagley, T. F.; Klein, E. J . Am.Chem. Soc., (1955), 77, 786. Geerts, J.; Van Beylen, M.; Smets, G.J. Polym. S c i . , (1969), 7 Part A-1, 2859. Smets, G.; Van Beylen, M. 23rd Congress of Pure and Applied Chem., Vol. 4, Butterworths, London, 1971, p. 405. Roovers, J. E. L.; Bywater, S. Polymer, (1973), 14, 594. Margerison, D.; Bishop, D. M.; East, G. C.; McBride, P. Trans. Faraday S o c . , (1968), 64, 1872. Alvarino, J . M.; Bello, Α.; Guzman, G. M. Eur. Polym. J.,, (1972), 8, 53. Wang, H. C.; Szwarc, M. Macromolecules, (1980), 13, 452. Al-Jarrah, M. M.; Young, R. N.; Fetters, L. J. Polymer Prepr., Am. Chem. Soc., Div. Polym. Chem., (1979), 20, 793. Graessley, W. W.; Hazleton, R. L.; Lindeman, L. R. Trans. Soc. Rheology (1967), 11, 267. Graessley, W. W.; Segal, L. Macromolecules, (1969), 2, 49. Hadjichristidis, N.; Roovers, J . E. L. J . Polym. Sci., Polym. Phys. Ed., (1974), 12, 2521. Berry, G.; Ferry, J . D.; Graessley, W. W.; Hadjichristidis, N.; Pearson, D.; Schrag, J . private communications. Brown, T. L. Adv. Organomet. Chem., (1965), 3, 365. Brown, T. L. J . Organomet. Chem., (1966), 5, 191. Kaspar, M.; Trekoval, J. Coll. Czech. Chem. Commun., (1976), 45, 1976. Kaspar, M.; Trekoval, J. C o l l . Czech. Chem. Commun., (1980), 45, 1047.
Received March 25, 1981.
In Anionic Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
