Polylactic acid was synthesized from commercial available cheap aqueous lactic acid(85 wt%～90 wt%) using succinic anhydride and SnCl2·2H2O as catalyst in the absence of organic solvents.As a result

polylactic acid with a molecular weight of 6×104 was prepared in 10 h.The effect of the amount of catalyst used

reaction temperature

and reaction time on the polymerization were investigated in detail.The amount of catalyst is the main factor that effecting the polymerization.The yields and molecular weights of the PLA obtained by succinic anhydride increase with the amount of succinic anhydride used in the range of 0 to 0.07 wt%.The trend is changed to decrease when the amount of the catalyst exceeds 0.07 wt%.The optimum amount of succinc anhydride is about 0.07 wt%

considering high Mw and high yield.The reaction time is another factor that effecting the polymerization.In a period of 0～10 h

the yield and molecular weight increase with the reaction time.In the longer reaction time that exceeds 10 h

the yields and molecular weights decrease with the time.The molecular weight of PLA reach a maximum after the reaction has been carried out for about 10 h.Polylactic acid obtained by succinic anhydride and SnCl2·2H2O was characterized by IR and NMR.This is a new catalytic system for the direct polymerization of the lactic acid.The catalyst is commercially available and used as received without further treatment.The monomer we used is cheap and renewable aqueous lactic acid.The new procedure is much simple

cheap and environmentally benign compared to those of the reported ones.This kind of polymer might be useful in biomedical applications.