Effects of residual monomer on the degradation of DL-lactide polymer

The effects of remaining monomer on hydrolysis of poly(DL-lactide) were examined by adding different amounts of monomer to purified polymer samples. The existence of monomer in the polymerization products was found to enhance hydrolytic degradation of the polymer. A porous texture was observed on the SEM photographs of degraded materials, which led to the conclusion that the remaining monomer enabled water molecules to gain better access to the polymer matrix through this porous structure. The effects of molecular weight and chemical composition of polylactides on the hydrolytic degradation were also studied. Poly(DL-lactic acid) with higher molecular weights showed longer retention of the initial properties such as molecular weight and tensile strength. Copolymerization of DL-lactide with glycolide enhanced the hydrolysis, probably because of increased hydrophilicity of the polymers. (C) 1998 SCI.