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

H.T. Oyama, S. Abe and T. Kanno
Rikkyo University, JP

Keywords: poly(lactic acid), stereocomplex, stereoblock copolymer, catalyst, molecular weight

Summary:

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 13C 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.