Effects of transesterification and degradation on properties and structure of polycaprolactone-polylactide copolymers

摘要

Ester bonds of biodegradable polymers, such as poly (a-hydroxy esters), synthesized by the coordinated anionic ring opening polymerization (CAROP), are subject to transesterification during synthesis. In this work, a series of poly(e-caprolactone)-poly(i.-lactide) (PCL-PLA) block and random copolymers with targeted molar mass of 10,000 Da was synthesized to study the mechanism of transesterification reactions via NMR and MALDI-TOF. Polylactide segments are more vulnerable to transesterification compared to polycaprolactone. As a result, the actual quantity of L-lactide in the polymers was less than the target for all studied copolymers because of the decarboxylation and consequent CO elimination from fragments of macromole-cules after transesterification. The presence of decarboxylation during transesterification was confirmed analytically and was reflected in the MALDI-TOF and ~(13)C NMR spectra. An analysis of the polymer structure pointed to dehydration reactions that led to the formation of cyclic structures and double bonds with possible crosslinking.