Studies on Thermal Degradation of Hydroxyl-Terminated Poly(L-Lactic Acid) Oligomer

Abstract

Thermal degradation of poly(L-lactic acid) (PLLA) oligomers into L-lactide (LA) with different oligomer terminal groups were studied. The thermal degradation behaviours of these oligomers were compared at 210-220 ºC under 0.3-0.5 kPa and the yield is as follows: OLLAPOH > OLLA > OLLACOOH. The results showed that poly-hydroxyl-terminated OLLA (OLLAPOH) has a 10-20 % higher yield than pure PLLA oligomer (OLLA) and two-carboxylic acid-terminated OLLA (OLLACOOH). It was considered that hydroxyl ends of the chains induce the reaction. OLLAPOH simultaneously starts depolymerization from each hydroxyl end to speed up the reaction, to shorten the time the substance remains at high temperature and to reduce the byproducts. This results in an increased L-lactide yield. A practical approach for L-lactide production by thermal degradation of OLLAPOH is adopted by using a degradation mechanism, which is an unzipping reaction beginning from the hydroxyl ends of the chains.