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 (Mw ) ≥ 100,000] in a relatively short reaction time (≤15 h) compared with simple Sn(II)‐based catalysts (SnO, SnCl2 · 2H2O), which produce PLLA with an Mw 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. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1673–1679, 2000 The melt polycondensation of L‐lactic acid was successfully conducted with Sn(II) catalysts activated by proton acids. The addition of p‐tolulenesulfonic acid was far more effective for increasing the molecular weight and preventing the discoloration of poly(L‐lactic acid) (PLLA). As a result, a high molecular weight of PLLA (Mw ≥ 100,000) was obtained within a short reaction time. The catalyst system is also superior to the conventional systems in regard to racemization of the resultant polymer.