In this study, poly(DL-lactide)/poly(ethylene glycol) (PDLLA/PEG) copolymers were synthesized. First, PDLLA homopolymers with three different molecular weights (Mw,: 7,300, 12,100 and 21,900) were synthesized by the ring opening polymerization of the dimer (i.e., DL-lactide) by using stannous chloride as catalyst. Average molecular weights of PDLLAs were determined by gel permeation chromatography (GPC). They were characterized by Fourier transform infrared and differential scanning calorimetry (DSC). These PDLLA homopolymers were then transesterified with PEG with a molecular weight range of 3,300-4,000. By changing the ratio of PEG to PDLLA, block copolymers with different chain structures were synthesized. DSC and GPC studies were performed to characterize these PDLLA/PEG copolymers. PDLLA and PDLLA/PEG particles in the size range of 2-10 pm were prepared by a modified solvent evaporation technique by using methylene chloride as solvent and methyl cellulose as emulsifier within the aqueous dispersion medium. Particle size was controlled by changing the solvent/polymer ratio, PDLLA molecular weight, and PEG content. Degradation of polymeric particles was investigated in a phosphate buffer at pH 7.4 and at 37OC. Particles prepared with low-molecular-weight PDLLAs degraded much faster. Introduction of PEG within the polymeric matrix caused a pronounced increase in the degradation rate. Bulk degradation was the dominant mechanism. 0 1996 John Wiley & Sons. Inc.