Preparation and characterization of poly(D,L-lactide-co-ethylene methyl phosphate)

Poly(D,L-lactide-co-ethylene methyl phosphate) was synthesized by ring-open ing polymerization of D,L-lactide (D,L-LA) and ethylene methyl phosphate (E MP) in bulk with Al((OPr)-Pr-i)(3) as initiator. The influence of reaction conditions such as polymerization time, polymerization temperature and init iator concentration on the yield and molecular weight were investigated. Th e reactivity ratios of the two monomers were determined by the Kelen-Tudos method. The homogeneous phase of the copolymer was confirmed by differentia l scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scann ing electron microscopy (SEM). DSC data showed that the glass transition te mperature of the copolymers increased with the increase of their LA content , which is in agreement with the Fox equation. Water absorption at room tem perature was used to evaluate the hydrophilicity of the copolymers. As expe cted, the hydrophilicity of the copolymer increased with the increase of EM P fraction therein. Copolymer hydrolysis was carried out in DMSO-d(6)/D2O, in the presence of trifluoroacetic acid; it was monitored by H-1 NMR, the d ata suggesting that side-chain cleavage proceeded faster than main-chain cl eavage, and the hydrolysis of the main chain was faster than that of poly(D ,L-lactide). These materials show potential use in drug delivery systems. ( C) 1998 Society of Chemical Industry.