Emulsion copolymerization of D,L-lactide and glycolide in supercritical carbon dioxide

Biodegradable polyesters were synthesized via an emulsion polymerization in supercritical carbon dioxide (SC-CO2). Copolymers of lactide and glycolide were synthesized in SC-CO2 with stannous octoate as the ring-opening catalyst and a fluorocarbon polymer surfactant as an emulsifying agent. The conversion of lactide and glycolide was monitored with respect to the reaction time and temperature with H-1 NMR spectroscopy. The conversion of glycolide surpassed 99% within 72 h for an SC-CO2 phase maintained at 200 bar and 70 degreesC. Under the same conditions, lactide conversion reached 65% after 72 h of polymerization. Unpolymerized monomer was removed after the reaction by extraction with an SC-CO2 mobile phase. The molecular weights of all the copolymers were measured by gel permeation chromatography. Weight-average molecular weights (M-w) ranged between 2500 and 30,200 g/mol and polydispersity indices ranged from 1.4 to 2.3 for polymerization times of 6 and 48 h, respectively. Although the molecular weight increased significantly during the first 48 h of reaction, there was no significant difference in the M-w for polymerization times of 48 and 72 h. Emulsion polymerization within the benign solvent SC-CO2 demonstrated improved conversion and molecular weight versus polymers synthesized without surfactant. The emulsion polymerization of lactide and glycolide copolymers in SC-CO2 is proposed as a novel production technique for high-purity, biodegradable polymers. (C) 2001 John Wiley & Sons, Inc.