Starting from cheaper D

L-lactic acid (D

L-LA)

lower molecular weight poly(D

L-lactic acid) (PDLLA) was directly synthesized via melt polycondensation.By using PDLLA as prepolymer

2

4-toluylene diisocyanate (TDI) as chain extender

and tetrahydrofuran (THF) as solvent

poly(D

L-lactic acid)s biodegradable material was synthesized through diisocyanate chain extension in solution state.When using different precipitators to terminate the solution chain extension

the solubility in chloroform

viscosity-average molecular weight (Mη)

structure

and heat properties of chain extension products were different.Before precipitation

the reaction mechanism of chain extension in solution state was similar to that in the melt state. However

different precipitators had different termination mechanisms. When precipitated by metchanol

the reaction between residual NCO group and OH group in metchanol could keep the structure of product basically unchanged.When water was used instead of metchanol

the complex reaction between residual NCO group and water was apt to produce cross-linking products.