Hydrolytic degradation of peroxide modified poly(L-lactide)

Abstract

Poly(L-lactide) (PLLA) was prepared by a tin(II)-octanoate initiated ring-opening polymerization in the melt and separately melt modified with tert-butylperoxy benzoate (0.1, 0.25 and 0.5 wt%) in order to deactivate the residual tin compounds and reduce melt degradation. Injection molded specimens of unmodified and peroxide-modified PLLA were prepared for a hydrolytic degradation study, where the changes in the weight, mechanical strength, molar mass and morphology were studied during the immersion in buffer solutions (pH 7.4) at 37 °C. The hydrolytic degradation of both the unmodified and the peroxide-modified PLLA was rapid. This was found to depend on the residual dilactide content, which in all samples was above 11% before the immersion. The peroxide modified samples underwent a more rapid hydrolytic degradation than the unmodified ones, which can be related to the morphological changes caused by the peroxide modification.