Abstract
Three stereocopolymers, namely PLA40, PLA25, and PLA10, were synthesized by ring opening polymerization of 40/60, 25/75 and 10/90 L-lactide/D-lactide feeds, respectively. PLA films with dimensions of 10 x 10 x 0.4 mm were prepared by compression molding and machining. Enzymatic degradation of the films was investigated at 37°C in a pH = 8.6 Tris/HCl buffer in the presence of proteinase K. It was confirmed that proteinase K preferentially degrades L-lactyl units as opposed to D-lactyl ones. With only 10% of L-lactyl units in its chains, PLA10 showed a non negligible enzymatic degradation, while degradation of PLA40 and PLA25 was much more pronounced. The higher water uptake ratio in the case of PLA40 and PLA25 could also have facilitated the enzymatic attack. On the other hand, there appeared to be a relationship between enantiomeric composition, Tg and hydrophilicity of PLA polymers. The more regular the polymer chains, the higher the Tg and, the less hydrophilic the polymer. The presence of residual monomer can also lower the Tg and enhance the hydroplilicity of PLA polymers.