Synthesis and characterization of some block copolymers of lactides with cyclic monomers using yttrium alkolxide as initiator

Block copolymers were prepared by sequential addition oft or D-lactide to a living epsilon-caprolactone prepared with Y(OC(2)H(4)OiPr)(3) initiator. I n contrast, epsilon-caprolactone (CL) was not polymerized when added to a l iving polyL-lactide (LA) prepared with the same initiator in the same condi tions. The polymerization of an equimolecular mixture of LA and CL using th e yttrium alkoxide initiator produces only the pure lactide homopolymer. Th e copolymerization of LA with trimethylene carbonate (TMC) exhibits a diffe rent type of behaviour. The synthesis of pure block copolymers by sequentia l addition of monomers is obtained if starting from a living polylactide se quence. When starting with TMC sequence, mixture of products leading to a b imodal MWD is obtained. The polymerization of an equimolecular mixture of L A and RMC leads to a copolymer with a block structure. The PLA sequence is formed first, followed by the subsequent addition of TMC monomer up to comp lete conversion All the prepared copolymers were characterized by SEC,H-1 a nd C-13 NMR techniques. No transesterification reactions were detected.