SYNTHESIS AND THERMAL-PROPERTIES OF POLY(ETHYLENE GLYCOL)-POLY(EPSILON-CAPROLACTONE) COPOLYMERS

Three different types of polyester-polyether copolymers were synthesiz ed by PEG initiated ring-opening polymerization of epsilon-caprolacton e: an A-B and an A-B-A block copolymer and an (A)(2)-B star copolymer, where A is a poly(epsilon-caprolactone) (PCL) and B is a poly(ethylen e glycol) (PEG) block. The monomer to initiator ratio was varied to ob tain copolymers with different PCL block length and weight fraction ra nging from 68-85 wt%. These PCL-PEG copolymers were characterized by m eans of g.p.c., n.m.r., d.s.c. and WAXD. In all types of copolymer the PCL constituent crystallizes first when cooling from the molten state . This leads to significant undercooling and imperfect crystallization of the PEG block. The mutual influence between PCL and PEG constituen ts is significantly stronger in the A-B-A block copolymers, having a c entral PEG block, and in the (A)(2)-B star copolymers. The effect of t he PCL/PEG ratio on the melting and crystallization behaviour of the c opolymers was investigated. The results obtained demonstrate that the thermal properties and morphology are affected significantly by the ch ain length of the PCL and PEG constituents in the copolymers and by th e type of copolymers (sequence of the different blocks). (C) 1997 Else vier Science Ltd. All rights reserved.