| Poly(L-lactic acid) is a typical green polymer since it is produced from renewable resources. PLLA is biodegradable, biocompatible and bioabsorbable. It also has good mechanical properties. Therefore it has found wide applications not only in biomedical field as drug delivery carriers, surgical implants and tissue engineering scaffolds, but also in industrial and agricultural field as general plastics. Because of its bright prospects, PLLA has attracted much attention from both industrial and academic fields.In this study, synthetic approaches, structure, performance and application of PLLA have been summarized and also indicates that how to get high molecular weight in a efficient and low-cost way, improve the toughness, introduce some functional group in the chain of PLLA are the important things in the development of the synthesis and modification of PLLA. In order to resolve these problems, we propose a new method which is called melt polycondensation-chain extension, use a diglycidylether or diglycidylester as a chain extender that can react with the hydroxyl and carboxyl end groups of prepolymer.Firstly, we studied on the effect of terminated group of OLLA to chain extension reaction. We got OLLA with molecular weight of 1000 by adding 1,4-BD, Succinic acid and Succinic anhydride, such as HO-OLLA-COOH, HO-OLLA-OH,HOOC-OLLA-COOH (1),HOOC-OLLA-COOH (2). We characterized them by ~1H-NMR. And then we use them to react with diglycidylester A. We found that the extender can react with OH group and COOH group, and more easily with COOH groups. And the chain extension product with Succinic anhydride has bigger instinct viscosity.We synthesized HOOC-terminated prepolymer with molecular weight from 1000 to 20000 through the change of molar ratios of L-lactic acid and succinic anhydride, and also we change the reaction time. We focus on the influence of molecular weight to chain extension reaction. We find that the molecular weight of the extension products increase with which of the prepolymer. The instinct viscosity increased about 8.89 times of OLLA with molecular weight of 1000, but the instinct viscosity increased little of OLLA with molecular weight of 20000. The thermo transition temperatures relates with the molecular weight of OLLA. When the molecular of OLLA is below 3000, the product has no melting points. When the molecular of OLLA is above 5000, the products have melting points from 138.03—144.95℃.Since a side hydroxyl group can be formed on the chain-extended PLLA molecules which can increase the Hydrophilic, and decrease the contact angle. The number of hydroxyl groups is related to the molecular weight of OLLA. As the molecular weight of OLLA decreases, the number of hydroxyl group increase, contact angle also decreases. As the molecular weight changes from 20000 to 1000, the contact angle decreases from 82.8°to 76.4°. Then, under 180℃, we choose the prepolymer with the theory design value of 10000 and expand chain reaction with different reaction time and the ratio of the extender and the prepolymer. We find that optimal experimental conditions is with the same mol of extender and the prepolymer within 1h.If the ratio is larger than 1 and the reaction time more than 1h, the cross-linking may be accompanied with the chain-extension reaction that the side hydroxyl group further react with the epoxy or carboxyl group to form a branched chain or cross-linking.
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