EROSION OF BIODEGRADABLE BLOCK-COPOLYMERS MADE OF POLY(D,L-LACTIC ACID) AND POLY(ETHYLENE GLYCOL)

Biodegradable block copolymers made of poly(ethylene glycol) monomethy lether (Me.PEG) and poly(D,L-lactic acid) (PLA) were investigated for their erosion properties. Wide angle X-ray diffraction (WAXD) and diff erential scanning calorimetry (DSC) investigations prior to erosion re vealed that despite the low content of crystallizable Me.PEG of 10%, M e.PEG5-PLA45 is a partially crystalline polymer. The erosion of the po lymer was investigated using cylindrical polymer matrix discs with a d iameter of 8 mm and a height of 1.5 mm. WAXD and DSC spectra obtained from eroded polymer matrix discs suggest that both polymer blocks sepa rate completely during erosion. The crystallinity of Me.PEG5-PLA45 was found to increase during erosion, which is probably due to the improv ed mobility of Me.PEG inside the polymer with a progressive degree of degradation. The erosion kinetics were found to be similar to that of PLA or poly(lactic-co-glycolic acid). During erosion the polymer matri x weight of dried samples remains constant for 11 weeks after which er osion sets in rapidly. From this observation one can conclude that the impact of the relatively small Me.PEG chains on Me.PEG5-PLA45 erosion is not pronounced. This is beneficial for all those applications that require the stability of the polymer matrix and in which the Me.PEG c hain is intended to bring about other effects such as the modification of the surface properties of PLA polymers. (C) 1998 Elsevier Science Limited. All rights reserved.