Physical properties and degradability of branched polylactide copolymers

Polylactides are hard, brittle polymers, and so blends of polylactides with other polymers and copolymers having soft segments (such as those based on lactones or cyclic carbonates) have been investigated. Random, diblock and triblock copolymers synthesized to date have all exhibited improved physical properties and degradability compared with polylactides. The thermal characteristics of stereocomplex (St) blends prepared by combining poly-L-lactide and poly-D-lactide copolymers are also significantly improved and the thermal properties of St specimens synthesized from block copolymers are further enhanced. Because these complexes exhibit intermolecular interactions between L-lactide (L-LA) and D-lactide (D-LA) chains, a higher degree of crystallinity is also obtained compared with the original copolymers. As a consequence, the degradability of the St is lower than that of the copolymers. The present work synthesized polylactide block copolymers having branched structures using glycerol and assessed the physical properties and degradability of these copolymers and of the St samples made by combining these materials. The haze values of the synthesized branched block copolymers showed a decreasing trend with decreasing lactide (LA) content in the range of 50 to 80 mol%, similar to that of the linear block copolymers. However, the crystallinity of the branched copolymers remained almost constant at approximately 40%, regardless of the LA content. The elongation of the branched copolymers increased with decreasing LA content, similar to that of linear copolymers. Therefore, branched block copolymers were able to increase their elongation without decreasing their crystallinity, even when the LA content was reduced. • The branched block copolymer contained high proportions of a soft amorphous phase. • Even copolymers with low LA content had high crystallinity. • Despite the high L-LA content of the copolymer, it degraded slowly.