Melt polycondensation of L-lactic acid with Sn(II) catalysts activated by various proton acids: A direct manufacturing route to high molecular weight poly(L-lactic acid)

Poly(L-lactic acid) (PLLA) was produced by the melt polycondensation of L-lactic acid. For the optimization of the reaction conditions, various catalyst systems were examined at different temperature and reaction times. It was discovered that Sn(II) catalysts activated by various proton acids can produce high molecular weight PLLA [weight-average molecular weight (M-w) greater than or equal to 100,000] in a relatively short reaction time (less than or equal to 15 h) compared with simple Sn(II)-based catalysts (SnO, SnCl2 . 2H(2)O), which produce PLLA with an M-w of less than 30,000 after 20 h. The new catalyst system is also superior to the conventional systems in regard to racemization and discoloration of the resultant polymer. (C) 2000 John Wiley & Sons, Inc.