Synthesis and properties of poly(lactic acid)

Poly(D,L lactic acid) was prepared by bulk polymerization of D,L lactide, b oth under atmospheric pressure and in vacuum. The obtained polymeric produc ts were characterized in terms of molecular weight, M-w, melting point, cal orimetric response and swelling behaviour. All products were amorphous. The ir molecular weights were determined by viscosimetry and ranged from 2 x 10 (3) to 9 x 10(4). Similarly, the melting points ranged from 90 to 210 degre es C. Swelling experiments, with specimens immersed in buffer solutions, sh owed that hydrolytic degradation started in a few days for the low M-w mate rial, whereas for the higher molecular weight products it took much longer and probably followed a two-stage mechanism. This study suggests that the h igh molecular weight material could be an interesting carrier for the prepa ration of controlled release products, in cases where prolonged delivery is necessary. (C) 1999 Kluwer Academic Publishers.