13 Organolithium Polymerization of є-Caprolactone 1
M A U R I C E M O R T O N and MEIYAN WU
Institute of Polymer Science, The University of Akron, Akron, O H 44325
Butyllithium and lithium t-butoxide were used as initiators to polymerize ε-caprolactone in H -furan and benzene solvents, at 25°C. Rapid reactions (50,000) were obtained. The relative reaction rates were: t-BuOLi/benzene>n-BuLi/enzene>t-BuOLi/H -furan >s-BuLi/H -furan. Although the i n i t i a l polymers had a narrow MWD characteristic of "living" polymers, all systems exhibited a rapid intramolecular and intermolecular ester interchange reaction of the active chain ends, leading to a broadening of molecular weight distribution with time.
Downloaded by UNIV OF LEEDS on November 1, 2014 | http://pubs.acs.org Publication Date: August 16, 1985 | doi: 10.1021/bk-1985-0286.ch013
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P r e v i o u s s t u d i e s (1-6) o f t h e a n i o n i c r i n g - o p e n i n g polymerization o f ε-caprolactone b y o r g a n o a l k a l i i n i t i a t o r s have shown t h a t t h i s system i s s u b j e c t t o a r i n g - c h a i n e q u i l i b r i u m , and t h a t t h e more e l e c t r o p o s i t i v e a l k a l i metal cations lead t o a f a s t e r attainment o f t h i s e q u i l i b r i u m . Yamashita and co-workers ( 3-5) p r o p o s e d t h a t l i n e a r polymer i s f i r s t formed and b r e a k s down t o c y c l i c o l i g o m e r s by a " b a c k - b i t i n g " r e a c t i o n o f t h e a c t i v e c h a i n ends, t h e r a t e o f such a d e p r o p a g a t i o n r e a c t i o n depending on t h e a l k a l i m e t a l p r e s e n t , e.g., b e i n g v e r y f a s t (
