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

• Published in: Polymer degradation and stability Vol. 95; no. 12; pp. 2596 - 2602
• Main Authors: Lipik, Vitali T., Widjaja, Leonardus K., Liow, Sing S., Abadie, Marc J.M., Venkatraman, Subramanian S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.12.2010; Elsevier
• Subjects: Applied sciences; Copolymers; Crosslinking; Decarboxylation; Degradation; Dehydration; Esters; Exact sciences and technology; Fragments; Macromolecules; Nuclear magnetic resonance; Organic polymers; Physicochemistry of polymers; Polycaprolactone; Polylactide; Polymerization; Preparation, kinetics, thermodynamics, mechanism and catalysts; Transesterification; Transesterification; Dehydration; Polylactide; Polycaprolactone; Decarboxylation; Ring opening polymerization; Lactone copolymer; Molecular structure; Lactic acid copolymer; Competitive reaction; Experimental study; Structure processing relationship; Random copolymer; Caprolactone copolymer; Preparation; Reaction mechanism; Anionic polymerization; Block copolymer
• DOI: 10.1016/j.polymdegradstab.2010.07.027
• ISSN: 0141-3910

Ester bonds of biodegradable polymers, such as poly (α-hydroxy esters), synthesized by the coordinated anionic ring opening polymerization (CAROP), are subject to transesterification during synthesis. In this work, a series of poly(ɛ-caprolactone)-poly( l-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 macromolecules after transesterification. The presence of decarboxylation during transesterification was confirmed analytically and was reflected in the MALDI-TOF and 13C 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.