HYDROLYTIC DEGRADATION OF PEROXIDE MODIFIED POLY(L-LACTIDE)

Poly(L-lactide) (PLLA) was prepared by a tin(II)-octanoate initiated r ing-opening polymerization in the melt and separately melt modified wi th tert-butylperoxy benzoate (0.1, 0.25 and 0.5 wt%) in order to deact ivate the residual tin compounds and reduce melt degradation. Injectio n molded specimens of unmodified and peroxide-modified PLLA were prepa red for a hydrolytic degradation study, where the changes in the weigh t, mechanical strength, molar mass and morphology were studied during the immersion in buffer solutions (pH 7.4) at 37 degrees C, The hydrol ytic 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 peroxid e 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.