12 NMR
Spectra of Styrene Oligomers and Polymers
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HISAYA SATO and YASUYUKI TANAKA Faculty of Technology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184, Japan Styrene oligomers having propyl end groups were prepared by the oligomerization of styrene i n i t i a t e d with ethyllithium and terminated with 1-bromopropane. The oligomers were separated according to molecular weight by GPC and the 2-5 mers were fractionated into diastereomers by l i q u i d chromatography. The diastereomers of the 2- and 3-mers were identified by 1H NMR and those of the 4- and 5-mers by using the results of the 2- and 3-mers. The 13C NMR signals of the oligomers were assigned by selective decoupling measurements and also by comparing the chemical shifts with each other. The methylene and phenyl C(1) signals of polystyrene were assigned on the basis of the oligomer. Polystyrenes prepared with benzoyl peroxide, n-butyllithium, and t r i f l u o roboron etherate had a random d i s t r i b u t i o n of r and m dyads with P values of 0.54, 0.56, and 0.45, respectively. r
The 13C NMR s p e c t r u m o f p o l y s t y r e n e was f i r s t r e p o r t e d by Bovey e t a l . i n 1970 ( 1 ) . The m e t h y l e n e and p h e n y l C ( l ) c a r b o n r e s o n a n c e s d i s p l a y s p l i t t i n g s w h i c h r e f l e c t t h e t a c t i c i t y d i s t r i b u t i o n and have been a s s i g n e d t o c o n f i g u r a t i o n a l s e q u e n c e s by many a u t h o r s ( 2 - 5 ) . However, t h e a s s i g n m e n t s d i f f e r e d f r o m e a c h o t h e r and d i f f e r e n t v a l u e s , r a n g i n g f r o m 0.45 t o 0.72, were r e p o r t e d f o r t h e probability o f a racemic dyad (P ) i n radically prepared polystyrene. These d i f f e r e n c e s may a r i s e f r o m t h e f a c t t h a t t h e o n l y p o l y s t y r e n e w i t h a known s t r u c t u r e i s i s o t a c t i c p o l y s t y r e n e prepared w i t h a Z i e g l e r - N a t t a c a t a l y s t . U s i n g t h i s p o l y m e r one c a n o n l y a s s i g n r e s o n a n c e s due t o t h e mmm t e t r a d and t h e mmmm p e n t a d , w h i l e o t h e r s i g n a l s a r e a r b i t r a r i l y a s s i g n e d by a s s u m i n g a Bernoullian o r other s t a t i s t i c a l d i s t r i b u t i o n . I n o r d e r t o a s s i g n r e s o n a n c e s i n t h e 1H and 13C NMR s p e c t r a o f p o l y s t y r e n e , s t y r e n e o l i g o m e r s h a v i n g m e t h y l end g r o u p s have been p r e p a r e d and s e p a r a t e d i n t o diastereomers up t o t e t r a m e r r
0097 6156/ 84/0247 0181 $06.00/0 © 1984 American Chemical Society In NMR and Macromolecules; Randall, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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( 6 - 9 ) . However, t h e s e o l i g o m e r s f a i l e d t o p r o v i d e u s e f u l i n f o r m a t i o n c o n c e r n i n g t h e s p e c t r a l a n a l y s i s o f p o l y s t y r e n e , because t h e m e t h y l end g r o u p s r e s u l t e d i n s p e c i a l c h e m i c a l s h i f t s f o r t h e 1H and 13C atoms l o c a t e d n e a r b y . A p p a r e n t l y , t h e s e o l i g o m e r s had d i f f e r e n t c o n f o r m a t i o n a l d i s t r i b u t i o n s than the polymer. I n t h i s c h a p t e r 1H and 13C NMR s p e c t r a o f p o l y s t y r e n e a r e a n a l y s e d u t i l i z i n g s t y r e n e o l i g o m e r s h a v i n g p r o p y l end g r o u p s .
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P r e p a r a t i o n and S e p a r a t i o n o f S t y r e n e
Oligomers
Styrene oligomers h a v i n g p r o p y l end g r o u p s were p r e p a r e d by i n i t i a t i n g o l i g o m e r i z a t i o n w i t h e t h y l l i t h i u m and t e r m i n a t i n g w i t h 1-bromopropane i n e t h y l e t h e r : CH CH L i + CH =CH * Ph 3
1
CH CH CH Br 3
2
2
(1)
The a v e r a g e d e g r e e s o f o l i g o m e r i z a t i o n were c o n t r o l l e d by v a r y i n g t h e m o l a r r a t i o o f s t y r e n e and t h e i n i t i a t o r . This anionic o l i g o m e r i z a t i o n method i s much e a s i e r t h a n t h e G r i g n a r d and o t h e r c o u p l i n g methods u s e d f o r t h e p r e p a r a t i o n o f o l i g o m e r s w i t h m e t h y l end g r o u p s , a l t h o u g h t h i s p r o d u c t i s a m i x t u r e o f o l i g o m e r s h a v i n g d i f f e r e n t degrees o f o l i g o m e r i z a t i o n . I n o r d e r t o s e p a r a t e t h e o l i g o m e r m i x t u r e , we examined t h e e l u t i o n b e h a v i o r o f t h e o l i g o m e r u s i n g a s t y r e n e - d i v i n y l benzene c o p o l y m e r g e l as a s t a t i o n a r y p h a s e and s e v e r a l e l u e n t s h a v i n g d i f f e r e n t p o l a r i t y a s shown i n F i g u r e 1. E l u e n t s h a v i n g t h e same p o l a r i t y as t h e g e l ( s o l u b i l i t y p a r a m e t e r ( S P ) = c a . 9 . 1 ) , s u c h a s c h l o r o f o r m and t e t r a h y d r o f u r a n c a u s e d t h e o l i g o m e r t o s e p a r a t e e a s i l y from h i g h e r m o l e c u l a r weight polymer. The o l i g o m e r s e l u t e d much e a r l i e r when t h e s e s o l v e n t s were u s e d t h a n when o t h e r t y p e s o f e l u e n t s were u s e d . This i n d i c a t e s that the oligomers are s e p a r a t e d by GPC by a s i z e e x c l u s i o n mechanism. N o n p o l a r e l u e n t s ( 2 , 2 , 4 - t r i m e t h y l p e n t a n e and i s o p r o p y l e t h e r ) and p o l a r e l u e n t s ( m e t h a n o l and a c e t o n i t r i l e ) e l u t e d t h e o l i g o m e r s more s l o w l y t h a n c h l o r o f o r m by a f a c t o r o f two. I t i s c l e a r t h a t t h e s e e l u e n t s c a u s e s e p a r a t i o n t o be c o n t r o l l e d by an a d s o r p t i o n mechanism w i t h a n e g l i g i b l e s i z e e x c l u s i o n e f f e c t . Using these e l u e n t s , we o b s e r v e d peak s e p a r a t i o n o r b r o a d e n i n g due t o t h e d i a s t e r e o m e r s f o r t h e d i m e r and h i g h e r o l i g o m e r s . U s i n g c y c l o h e x a n e and a c e t o n e , w h i c h have s i m i l a r SP v a l u e s t o t h a t o f t h e g e l , we s e p a r a t e d t h e o l i g o m e r s i n t o two g r o u p s ; one a t an e l u t i o n volume a r o u n d 20 ml due t o h i g h e r m o l e c u l a r w e i g h t o l i g o m e r s and t h e o t h e r a r o u n d 30 - 40 ml due t o l o w e r molecular weight ones. This discontinuous molecular weighte l u t i o n volume r e l a t i o n c a n be e x p l a i n e d by a h y b r i d mechanism o f s i z e e x c l u s i o n and a d s o r p t i o n e f f e c t s . Larger oligomers cannot p e r m e a t e i n t o t h e g e l and c o n s e q u e n t l y e l u t e e a r l i e r , e x p e r i e n c i n g
In NMR and Macromolecules; Randall, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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12.
SATO A N D TAN A K A
NMR Spectra of Styrene Oligomers and Polymers
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o n l y a s l i g h t a d o r p t i o n e f f e c t , w h i l e s m a l l e r o l i g o m e r s permeate into t h e g e l and s u f f e r b o t h s i z e e x c l u s i o n and a d s o r p t i o n effects. They e l u t e a t a l m o s t t h e same e l u t i o n volume r e g a r d l e s s of t h e m o l e c u l a r weight. The o l i g o m e r m i x t u r e p r e p a r e d a c c o r d i n g t o E q u a t i o n ( 1 ) was f i r s t s e p a r a t e d i n t o p u r e η-mers by G P C u s i n g c h l o r o f o r m as an eluent. The p u r e 2 - 5 mers were s e p a r a t e d b y a d s o r p t i o n chroma tography u s i n g a r e c y c l i n g technique. D i i s o p r o p y l e t h e r was u s e d as an e l u e n t , b e c a u s e t h i s e l u e n t p r o v i d e d a column w i t h a h i g h e r number o f t h e o r e t i c a l p l a t e s t h a n d i d t r i m e t h y l p e n t a n e , a c e t o n i t r i l e , and m e t h a n o l . The d i m e r s and t r i m e r s were s e p a r a t e d i n t o 2 and 3 f r a c t i o n s , r e s p e c t i v e l y , a f t e r 12 r e c y c l e s ( F i g . 2 a and b) . The t e t r a m e r , w h i c h h a s 6 d i a s t e r e o m e r s , was s e p a r a t e d a c c o r d i n g l y i n t o 6 f r a c t i o n s a f t e r 24 r e c y c l e s , a l t h o u g h t h e s e p a r a t i o n o f t h e second and t h e t h i r d f r a c t i o n s was n o t s o good ( F i g . 2 c ) . The s e p a r a t i o n o f t h e p e n t a m e r was c a r r i e d o u t i n two stages o f f r a c t i o n a t i o n . I n t h e f i r s t s t a g e , t h e f i r s t and t h e n i n t h f r a c t i o n s were c o l l e c t e d and t h e r e m a i n i n g p o r t i o n was s e p a r a t e d i n t o 3 p a r t s l a b e l l e d A , B , and C. The t h r e e p a r t s were s u b s e q u e n t l y s e p a r a t e d i n t o f r a c t i o n s 2 and 3, f r a c t i o n s 4, 5, and 6, and f r a c t i o n s 7 and 8, r e s p e c t i v e l y , d u r i n g t h e second s t a g e o f fractionation (Fig. 2 d ) . NMR S p e c t r a o f t h e D i m e r and T r i m e r The d i a s t e r e o m e r s o f t h e d i m e r were i d e n t i f i e d t h r o u g h t h e s p l i t t i n g p a t t e r n o b s e r v e d f o r t h e m e t h y l e n e p r o t o n s f l a n k e d b y two methine protons; t h e methylene protons o f t h e r dyad a r e e q u i v a l e n t , w h i l e t h o s e o f t h e m dyad a r e n o n e q u i v a l e n t . Ph H a H CH CH CH -Ç - Ç - Ç-CH.CH CH H H a Phi ^ r isomer 0
3
Q
H Ha H C H C H C H -6 - C - Ç-CH CH CH ^ P h Hb Ph ^ m isomer Q
Q
d
J
F i g u r e 3 shows m e t h i n e and m e t h y l e n e H - l NMR s p e c t r a o f t h e 2 d i m e r f r a c t i o n s w h i c h g a v e m e t h y l e n e p r o t o n r e s o n a n c e s a r o u n d 1.8 ppm. F r a c t i o n 2-1 showed a n AA'X m e t h y l e n e r e s o n a n c e p a t t e r n , w h i l e f r a c t i o n 2-2 showed a n ABX s y s t e m . The m e t h y l e n e p r o t o n s i g n a l s d e c o u p l e d f r o m t h e m e t h i n e p r o t o n d i s p l a y more c l e a r l y t h e d i f f e r e n c e between t h e s p l i t t i n g p a t t e r n s ; F r . 2-1 e x h i b i t e d AA* s p l i t t i n g s , w h i l e F r . 2-2 e x h i b i t e d a n AB q u a r t e t . Therefore, f r a c t i o n s 2-1 and 2-2 were a s s i g n e d t o t h e r and m i s o m e r s , respectively. S i m i l a r l y , t h e t r i m e r f r a c t i o n s , F r . 3-1, 3-2, and 3-3, were i d e n t i f i e d a s rr, rm, and mm i s o m e r s b y t h e s p l i t t i n g p a t t e r n o f t h e i r m e t h y l e n e p r o t o n s i g n a l s a s shown i n F i g u r e 4. The m e t h i n e p r o t o n s o f t h e d i m e r and t h e t r i m e r r e s o n a t e d i n two c h e m i c a l s h i f t r a n g e s . One o c c u r r e d between 2.5-2.2 ppm, w h i c h i s a s s i g n e d t o t h e m end and t h e mm c e n t e r and t h e o t h e r b e t w e e n 2.2-2.0 ppm, w h i c h i s a s s i g n e d t o t h e r end and t h e ( r r + rm) c e n t e r . I t i s n o t e w o r t h y t h a t t h e c e n t r a l m e t h y l e n e p r o t o n o f
In NMR and Macromolecules; Randall, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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_l
10
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20 30 40 Elution
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50 100 Volume (ml)
150
Figure 1. R e l a t i o n s h i p between m o l e c u l a r weight and e l u t i o n volume o f s t y r e n e o l i g o m e r s i n c h l o r o f o r n ( c u r v e 1; SP= 9 . 1 ) , t e t r a h y d r o f u r a n ( 2 ; 9 . 1 ) , c y c l o h e x a n e ( 3 ; 8 . 2 ) , acetone (4; 9.4), diisopropyl ether ( 5 ; 7 . 3 ) , 2,2,4t r i m e t h y l p e n t a n e ( 6 ; 7.0), a c e t o n i t r i l e ( 7 ; 11.8), methanol ( 8 ; 12.9) . ( c o l u m n : 1 0 mm i . d . χ 50 cm) . R e p r o d u c e d w i t h p e r m i s s i o n f r o m R e f . 1 2 C o p y r i g h t 1 9 8 1 , H u t h i g & Wepf Verlag. (a)
(b) 3 mer
2 mer
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12. c y c l e
(c) 4 mer
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24. c y c l e
(d) 5 mer 1st Fractionation 10.
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26. c y c l e
A 2nd
F i g u r e 2. S e p a r a t i o n o f s t y r e n e oligomers into diastereomers. (Column: 21rami . d . χ 60 cm χ 3; Eluent: d i i s o p r o p y l ether)
Practionatioi
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cy.
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