| Polylactic acid(PLA), a kind of synthetical aliphatic polyesters, bears wonderful biologic compatibility and biodegradable properties,which is harmless and non-toxic to the environment. Hence widely having been used to the tissue engineering as scaffold material,carrier for pharmaceutical release an internal fixation of bone fracture. The development of PLA and synthesis of its monnmer-lactide are catching more attention in this field. The field of lactide is one of the most importantfactors that hamper the PLA from widely use for a long time. In this paper,a series of apparatus which can boost the product ratio to the utmost was focused on. Meanwhile the factors affecting the molecular weightof PLA in the polymerization were also discussed.It has been used as one of the most important biomedical materials. At the same time, with physical mechanical properties similar to popular plastics,PLA polymers can be employed as a promising cost-effective alternative to commodity petrochemical-based plastics so as to lessen the dependence of plastics on oil and diminish the pollution caused by waste plastic products. PLA will become an industrial material with considerable perspective.We prepared degradable L-PLA by L-lactic acid in this paper. Main research contents and results are summarized as following:(1) Kinetics of direct polycondensation of lactic acid was studied in the paper.The direct polylactic acid(PLA) was made from lactic acid under atmospheric pressure without catalyst. The results showed that the polycondensation proceeds as a third order reaction at 124℃with 14．15%-62．75% conversion:-d[COOH]/dt=1．057×10-5 [COOH]3．Reactive equilibrium constant K of different temperature and reactive energy E were calculated.The paper compared the relationship of molecular weight and time in the theory and practice.(2) L-LA was synthesized from L-lactic acid. The optimal synthetic condition and process engineering were studied. The former optimal dehydration temperature is 110～120℃, dehydration time is 2 hours, the latter dehydration time is 4 hours, vacuum is 1．3kPa～6．3kPa, Sn(Oct)2 is the catalyst and the dose is 1%, depolymerization temperature is 220℃, vacuum 10-5Pa. The yield of L-Lactide was up to 87．16%. The result dedicated the the optical purity of L-Lactide which had been recrystallized thrice can reach 98．5%.(3) Synthesis of PLLA used L-LA as material. The optimal synthetic condition and process engineering were studied and then got the best synthetic condition. The dose of Sn(Oct)2 reach to 0．8%, polymerization temperature is 140℃, polymerization time is 48 hours. The highest number-average molecular weight has exceeded 158540．(4) The structure, purity, physical chemistry properties of cyclic diester and polymer were confirmed through optical rotation, DSC, IR, 1H-NMR, GPC,x-ray. |
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