Synthesis Of Lactide And Novel Medicinal NH₂-PEG-Modified Polylactide

Polylactide (PLA) is one of the few polymer materials with good biocompatibility and biodegradability. As biomaterial, the applications of PLA and its copolymers are more and more widely, especially in tissue engineering scaffold, carrier for pharmaceutical release and internal fixation of bone fracture. Lactide, an intermediate of PLA and its copolymer, of course are catching more attention. The costs of lactide are one of the most important factors that hamper the PLA from large scale production and widely use for a long time. To solve these problems, exploring the technique of large scale production of lactide is necessary for there is no technique in China to produce lactide in large scale now. In this paper, we tried to figure out a set of synthetic condition for large scale production of lactide using the equipments designed by our lab.1 The synthetic condition of large scale production of lactide was studied with single factor optimizing method according to the yield and purity of lactide. Three factors we have chosen: dehydration temperature and time, and distill temperature. The optimizing results was dehydration temperature 120-125℃, dehydration time 4 hours, distill temperature 200-210℃.2 A catalyst with high-power and low-cost—zinc lactate was selected in our experiments from several kinds of catalysts. And the optimum proportion is 2% which can increase the yield and purity of lactide under the same condition.3 Optimizing the synthetic condition of large scale production of lactide: judged by the yield and lactic acid content of lactide, an orthogonal experiment with three factors which were dehydration temperature, dehydration time and distill temperature were designed. The results indicated that the dehydration time and distill temperature were the main factors affecting the yield and acid content of lactide. From the points of energy consumption and lactide yield, the best synthetic condition in large scale was as follows: dehydration temperature is 120-125℃, dehydration time is 4 hours, distill temperature is 210-220℃. Then, the melting point was tested by Thiele tube and lactide were characterized by IR spectrum, TG and DSC, XRD spectrum respectively. The result indicated the purity of lactide which had been recrystallized thrice can meet the requirement of synthesizing high molecular PLA and its melting point is 126.3℃.4 In order to improve the characters of PLA in application, it was modified with polypropylene glycol, then purified and characterized by IR and 1H-NMR spectrum.