POLY(DL-LACTIDE) POLY(ETHYLENE GLYCOL) COPOLYMER PARTICLES .1. PREPARATION AND CHARACTERIZATION/

In this study, poly(DL-lactide)/poly(ethylene glycol) (PDLLA/PEG) copo lymers were synthesized. First, PDLLA homopolymers with three differen t molecular weights (Mw(n): 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 PDL LAs 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 structur es were synthesized. DSC and GPC studies were performed to characteriz e these PDLLA/PEG copolymers. PDLLA and PDLLA/PEG particles in the siz e range of 2-10 mu m were prepared by a modified solvent evaporation t echnique by using methylene chloride as solvent and methyl cellulose a s emulsifier within the aqueous dispersion medium. Particle size was c ontrolled by changing the solvent/polymer ratio, PDLLA molecular weigh t, and PEG content. Degradation of polymeric particles was investigate d in a phosphate buffer at pH 7.4 and at 37 degrees C. Particles prepa red with low-molecular-weight PDLLAs degraded much faster. Introductio n of PEG within the polymeric matrix caused a pronounced increase in t he degradation rate. Bulk degradation was the dominant mechanism. (C) 1996 John Wiley & Sons, Inc.