Synthesis and characterization of some block copolymers of lactides with cyclic monomers using yttrium alkoxide as initiator
Résumé
Block copolymers were prepared by sequential addition of L-or D-lactide to a living caprolactone prepared with Y(OC 2 H 4 OiPr) 3 initiator. In contrast, -caprolactone (CL) was not polymerized when added to a living polyL-lactide (LA) prepared with the same initiator in the same conditions. The polymerization of an equimolecular mixture of LA and CL using the yttrium alkoxide initiator produces only the pure lactide homopolymer. The copolymerization of LA with trimethylene carbonate (TMC) exhibits a different type of behaviour. The synthesis of pure block copolymers by sequential addition of monomers is obtained if starting from a living polylactide sequence. When starting with TMC sequence, mixture of products leading to a bimodal MWD is obtained. The polymerization of an equimolecular mixture of LA and TMC leads to a copolymer with a block structure. The PLA sequence is formed first, followed by the subsequent addition of TMC monomer up to complete conversion. All the prepared copolymers were characterized by SEC, 1 H and 13 C NMR techniques. No transesterification reactions were detected.
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