Abstract
Three stereocopolymers, namely PLA50-rac, PLA50-mes, and PLA62.5, were synthesized by ring opening polymerization of racemic-lactide (or DL-lactide), meso-lactide, and a mixture of 25/75 L/DL-lactides, respectively. The synthesis was carried out at 140°C during one week, using zinc powder as initiator. After purification, the polymers were compression molded to yield circular films of c.a. 0.4 mm thickness and 75 mm diameter, from which 10 x 10 mm2 square samples were then cut. The enzymatic degradation of these PLA polymers was investigated at 37°C in a pH = 8.6 Tris/HCl buffer solution in the presence of proteinase K. Degradation of PLA50-mes was found to be much faster than that of PLA50-rac, PLA62.5 degrading at an intermediate rate. It was assumed that proteinase K degrades preferentially L-L, L-D and D-L bonds as opposed to D-D ones. On the other hand, the much higher water uptake ratio of PLA50-mes as compared to those of PLA50-rac and PLA62.5 could have facilitated the enzymatic attack in the former case.