Abstract: Poly（lactic acid）(PLA) was prepared by ringopening polymerization of D, L-lactide with zinc oxide (ZnO) pillared organic saponite under microwave assistance. The molten chain extension reaction of PLA was investigated with hexamethylene diisocyanate (HDI) and 4, 4-diphenylmethane diisocyanate (MDI) as chain extenders. The effect of reaction time and addition amount of chain extender on the molecular weight of PLA was also studied. The optimum parameters of the chain extending reaction were as follows: the ratio between nNCO to nOH was 2.5：1, the reaction temperature was 180 ℃, the chain extension time of MDI was 45 min, and the chain extension time of HDI was 30 min. Kinetics experiments indicated that the chain extender showed the apparent rate constants of MDI and HDI were 6.081×10^3 g/(mol·min)，6.98×10^3 g/(mol·min), respectively.

Key words: poly(lactic acid), isocyanate derivatives, extender chain reaction, kinetics, structure