Starting from L-lactic acid

poly (L-lactic acid) with low polymerization degree was first synthesized through direct melt polycondensation with composite catalyst.Then PLLA with higher molecular weight was obtained by solid-state polymerization with different temperature controlling. The conditions of solid-state polymerization were especially studied.Viscosity measurements and gel permeation chromatography (GPC) were used to measure intrinsic viscosity and molecular weight of resulting PLLA polymers

respectively.The differential scanning calorimetry (DSC) was used to characterize the melt properties and crystallinity of PLLA.The results showed that under absolute pressure 80 Pa with subsection temperature controlling (first at105℃ for2.5h

then at145℃ for35h

the molecular weight ( M

w

) of PLLA is 426

000

which is 36 times higher than that of PLLA first prepared by melt polycondensation. The T

m

and crystallinity ( X

c

) are 189.6℃ and 69.25%

respectively.Preparation of high molecular weight polylactic acid provides direction for its industrial production of the new method.