Melt/solid polycondensation of L-lactic acid: an alternative route to poly(L-lactic acid) with high molecular weight

A high polymer of poly(L-lactic acid)(PLLA) is successfully obtained by the melt/solid polycondensation of L-lactic acid (LA) catalyzed by a tin chlor ide dihydrate/p-toluenesulfonic acid binary system. In this process, a poly condensate with a molecular weight of 20,000 Da is first prepared by ordina ry melt-polycondensation, crystallized by heat-treatment around 105 degrees C, and heated at 140 or 150 degreesC for 10-30 h for further polycondensati on. A high-quality polymer of PLLA can be obtained in high yield in a relat ively short reaction time and its molecular weight exceeds 500,000 Da which is comparable with that of the PLLA obtained by the lactide method but has never been attained by the simple melt-polycondensation. (C) 2001 Elsevier Science Ltd. All rights reserved.