| Poly L-lactic acid(PLLA) have wonderful biologic compatibility andbiodegradable properties, which is harmless and non-toxic to the environment asit can finally biodegrade into CO2 and H2O. Its crude material resource is L-lacticacid obtained from starch with fermentation. It has been used as one of the mostimportant biomedical materials. At the same time, with physical mechanicalproperties similar to popular plastics, PLLA can substitute for them. Poly L-lacticacid will become an industrial material with considerable perspective. In thisdissertation, the material of PLLA's polymerization, L-lactide was discussed.In this paper, L-lactide was synthesized by reduced pressure method. Itincluded the synthesis of L-lactide, the purification of L-lactide and the analysisof L-lactide's et. al.The synthesis of L-lactide under reduced pressure has been studied, and theeffects of the pressure, temperature, the sort of catalyst and the catalystconcentration also have been studied. It showed that the results were better underreduced pressure. Its highest yield was up to 69.3％and the needed time wasshorter. It showed that high vacuum can give high yield and in all used catalyst,ZnO was the best one, and the temperature must be below 240℃.To purification of crude L-lactide, the method of the filter under reducedpressure, recrystallization, and every component to purify based on the differentphysical properties have been selected. It can be seen that the last one is best.The product was a colorless needle crystal. Its melting point was 95～96℃andits optical purity accorded with need. Finally, the purified L-lactide wasmensurated, the results accorded with the literature data.All of above-mentioned results show, the L-lactic acid was synthesis by thecatalyzer ZnO under high vacuum to dehydrate and polymerize at 130～140℃, L- lactide in 1 hour, and to decompose at 230～240℃in 1.5 hours. Then it can givehigh yield.
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