Low-molecular-weight polyesters were obtained by the ring-opening homopolymerization and copolymerization reaction of ?-caprolactone, rac- or L-lactide, and glycolide in the presence of poly(ethylene glycol) with an enzyme catalyst, a lipase from Candida antarctica, Pseudomonas cepacia, or Pseudomonas fluorescens. The influence of several parameters, including time, temperature, and enzyme and monomer concentration, on the polymerization rate was studied. The resulting polymers were characterized by 1H-NMR or 13C-NMR, Fourier transform infrared spectroscopy, matrix-assisted laser desorption/ionizationtime of flight mass spectroscopy, and gel permeation chromatography. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012