| Poly(lactic acid-glycolic acid)(PLGA) was synthesized through direct melt copolycondensation for 10h at 170℃and absolute pressure of 70Pa with L-lactic acid(LA) and glycolic acid(GA)(molar ratio of 20 to 80)as raw materials. The effect of kind of catalyst,quantity of catalyst and the ratio of composite catalyst on the [η] and color of the product was investigated, the results showed that the catalytic conditions SnCl2/PLGA=0.4w%,SnCl2/TSA=1∶1, a product of high viscosity(0.352dL/g) was obtained with deeper color,and the color of the product was improved by adding appropriate amount of antioxidant 1010, but the viscosity lower than the pre-accession.The structure of PLGA was characterized by IR and NMR, the results proved that the product is a copolymer, but not their homopolymer, and the ratio of glycolic acid in the copolymer is greater than in the materials; By DSC and X-ray diffraction analysis of its thermal properties and its crystalline, the results showed that the PLGA (20∶80) is a non-crystalline polymers.The solid-phase polycondensation of PLGA prepolymer was carried out and the appropriate conditions was obtained. Heat treatment time of the prepolymer is 2 hours and solid-state reaction temperature is 110℃in the protection of nitrogen for 30 hours. The [η] of PLGA was increased to 1.84 times. DSC analysis showed that under certain temperature, the melting point of the product was increased with increasing reaction time, but the melting point will decrease when the reaction time was more than 30 hours.The chain extension of PLGA was carried out in melt state with 2,4-toluene diisocyanate (TDI) as chain extension agent. The [η] of PLGA was increased to 2.65 times in the proper condition (NCO/OH=1∶1 mol ratio; time: 60min; temperature:160℃). The results of IR,DSC and X-Ray investigations showed that through chain-extension reaction, the TDI was introduced in PLGA chain and the Tg was moderately increased. However, the polymer is still non-crystalline.
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