Highly Crystalline Poly(lactic acid)(PLA) Alloys Containing Stereocomplexes

摘要

Stereoblock poly(lactic acid) (sb-PLA) composed of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) in a block sequence is expected to be a bio-based material with high thermal stability. This work reports the synthesis of sb-PLA with high molecular weight and high degree of complex formation by catalytic polycondensation using a combination of enantiometric PLA oligomers with different oligomer lengths. The thermal and structural changes in these materials upon reaction were investigated by DSC, GPC, and ~(13)C NMR spectroscopy. It was revealed that the PLA oligomers synthesized with a widely used tin catalyst causes a side reaction to form dimeric lactide so that the molecular weight did not increase efficiently during the polycondensation. By contrast, the PLA oligomers synthesized with a methanesulfonic acid catalyst studied for the first time in the present study suppresses side reactions, thereby forming sb-PLA with higher molecular weight at a higher yield. Furthermore, it was also shown that the molecular weight of the starting PLA oligomers significantly affects the final molecular weight and sc crystallinity of sb-PLA.