23 Anionic Polymerization of Triphenylmethyl Methacrylate YOSHIO OKAMOTO, KOJI OHTA, KOICHI HATADA, and HEIMEI YUKI
Downloaded by CORNELL UNIV on July 24, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch023
Department of Chemistry, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan
Stereospecific polymerization of various methacrylates has been extensively studied (1). Among many, triphenylmethyl meth acrylate (TrMA) is one ofthemost interesting monomers and brings about some unusual results as follows: This monomer forms only
highly isotactic polymers with butyllithium (BuLi) not only in toluene but in tetrahydrofuran (THF) (2,3), and even with radical i n i t i a t o r it gives a polymer rich in isotacticity (2,3,4,5). This unique nature of TrMA has been ascribed to the bulky triphenylmethyl group. The large ester group also affects greatly i t s reactivity in the copolymerization with other methacrylates, such as methyl methacrylate (MMA) or α-methylbenzyl methacrylate (MBMA) with BuLi (6,7,8). Some of the copolymers of (S)-MBMA and TrMA shows large positive optical rotations, which are opposite in sign to the rotation of the homopolymer of (S)-MBMA. This positive rotation is attributed to the isotactic sequence of TrMA units which has h e l i c a l conformation spiraled in single screw sense (9, 10, 11). Recently, we found that the polymerization of TrMA with chiral anionic catalysts gave an optically active polymer the chirality of which is caused by h e l i c i t y (12). This is the f i r s t example of optically active vinyl polymer the activity of which arises only from the h e l i c i t y . This article describes the detailed results of the polymerization of TrMA by chiral anionic catalysts in addition to a brief review on our e a r l i e r studies described above. P o l y m e r i z a t i o n o f TrMA with BuLi
( 2 , 3)
Table I shows the r e s u l t s o f the p o l y m e r i z a t i o n o f TrMA with BuLi.
Both in toluene and THF h i g h l y
isotactic
polymers were
0097-6156/81/0166-0353$05.00/0 ©
1981 American Chemical Society
McGrath; Anionic Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
354
ANIONIC POLYMERIZATION
obtained. The r a d i c a l p o l y m e r i z a t i o n i n i t i a t e d b y AIBN a l s o a f f o r d e d a p o l y m e r r i c h in i s o t a c t i c i t y . These a r e u n u s u a l r e s u l t s b e c a u s e most m e t h a c r y l a t e s f o r m p o l y m e r s r i c h in s y n d i o t a c t i c i t y w i t h B u L i in THF a n d w i t h r a d i c a l c a t a l y s t s ( 1 ) . TrMA d i d n o t p o l y m e r i z e w i t h p h e n y l m a g n e s i u m b r o m i d e , w h i l e most m e t h a c r y l a t e s do ( 1 ) . Table I P o l y m e r i z a t i o n o f TrMA by B u L i Temp. Time Yield Tacticity,% Solvent (°C...) I H S (hr) (%) Toluene -78 21 24 96 2 2 Toluene 0 24 58 93 4 3 Toluene 60 92 144 64 22 14 THF -78 56 96 3 1 2.5 THF 0 98 24 81 13 6 a
Downloaded by CORNELL UNIV on July 24, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch023
b
a
b
TrMA, 5mmol; s o l v e n t , 1 0 m l ; TrMA/BuLi=20. C a t a l y s t , AIBN.
C o p o l y m e r i z a t i o n o f TrMA a n d MMA w i t h B u L i
( 6 , 7)
C o p o l y m e r c o m p o s i t i o n c u r v e s in the c o p o l y m e r i z a t i o n o f MMA ( M i ) and TrMA ( M ) w i t h B u L i a t -78°C... a r e shown in F i g u r e 1. From t h e s e c u r v e s the monomer r e a c t i v i t y r a t i o s w e r e d e t e r m i n e d t o b e r i = 6 . 2 8 and r 2 = 0.13 in t o l u e n e and r i = 0.62 a n d r = 0.62 in THF. I n THF b o t h the monomers showed s i m i l a r r e a c t i v i t y . The c o m p o s i t i o n a l and c o n f i g u r a t i o n a l a n a l y s e s o f the c o p o l y m e r s i n d i c a t e d t h a t the c o p o l y m e r i z a t i o n a p p r o x i m a t e l y f o l l o w s the t e r m i n a l m o d e l in t h i s s o l v e n t . The t a c t i c i t y o f a c o p o l y m e r c a n b e c a l c u l a t e d in terms o f c o n d i t i o n a l p a r a m e t e r s , P j : Ρ χ and 2 1 , f ° e sequence d i s t r i b u t i o n and c o n f i g u r a t i o n a l p a r a m e t e r s , 0±j : On, σ , 1 2 , 21. The P i j is the p r o b a b i l i t y o f f i n d i n g the Mj u n i t as the n e x t n e i g h b o r o f the M u n i t a n d c a n be c a l c u l a t e d f r o m monomer r e a c t i v i t y r a t i o s , τ\ and r v a l u e s ( 1 3 ) . The 0±j is the p r o b a b i l i t y o f g e n e r a t i n g a meso d y a d when a new monomer u n i t Mj is f o r m e d a t the M e n d o f a g r o w i n g c h a i n . The On and σ are o b t a i n a b l e f r o m the dyad o r t r i a d c o n t e n t s o f MMA a n d TrMA homop o l y m e r s , and a* **
