Lipase-catalyzed synthesis of aliphatic polyesters via copolymerization of lactide with diesters and diols

Abstract

Aliphatic lactate-bearing copolyesters were successfully synthesized via copolymerization of L-lactide (LLA) with diesters and diols using Candida antarctica lipase B (CALB) as the catalyst. The resultant copolymers had a Mw up to 38,000 Da with Mw/Mn between 1.5 and 2.0, and contained L-lactate units (up to 53 mol%), C6-C12 diester units, and C4-C6 alkylene units in the polymer chains. The lactate repeat units were present primarily as lactate-lactate diads in the polymers. The LLA-diester-diol copolymers were purified in good yield (70-85%) and all purified copolymers were optically active. Hydrolytic degradation study shows that LLA-diethyl adipate-1,6-hexanediol (LLA-DEA-HD) copolymers are degradable polymers as the molecular weight (Mw) of the copolymer with 53% lactate units decreased by ∼70% upon incubation in PBS solution under physiological conditions (37 C, pH of 7.4) for 80 days. The LLA-diester-diol copolymers are thermally stable up to at least 300 C with the temperature of maximum degradation rate ranging from 380 to 410 C. The copolymers exhibit a wide range of physical properties (e.g., from white solid to wax and liquid) depending on their structure and composition. In particular, the LLA-DEA-HD and LLA-DEA-1,4-butanediol copolymers with ∼50 mol% lactate units are colorless, viscous liquids at ambient temperature. Biodegradable liquid polymers are potentially useful biomaterials for drug delivery to treat ocular ailments because of their good compatibility with sensitive soft tissues. © 2013 Elsevier Ltd. All rights reserved.