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 catal
yst and a fluorocarbon polymer surfactant as an emulsifying agent. The conv
ersion 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 reactio
n by extraction with an SC-CO2 mobile phase. The molecular weights of all t
he copolymers were measured by gel permeation chromatography. Weight-averag
e molecular weights (M-w) ranged between 2500 and 30,200 g/mol and polydisp
ersity indices ranged from 1.4 to 2.3 for polymerization times of 6 and 48
h, respectively. Although the molecular weight increased significantly duri
ng 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 we
ight versus polymers synthesized without surfactant. The emulsion polymeriz
ation 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.