丁二酸酐与SnCl_2·2H_2O共催化含水乳酸缩聚制备高分子量聚乳酸

SYNTHESIS OF HIGH MOLECULAR-WEIGHT POLYLACTIC ACID FROM AQUEOUS LACTIC ACID CO-CATALYZED BY TIN(Ⅱ) CHLORIDEDIHYDRATE AND SUCCINIC ANHYDRIDE

用丁二酸酐与SnCl2.2H2O共催化含水乳酸本体缩聚,合成黏均分子量为6×104的聚乳酸.合成反应时间短,聚乳酸产率高、纯度好.单体为含水10%～15%的乳酸.聚合方法环境友好,不使用任何共沸溶剂.讨论了催化剂用量、反应温度、聚合时间等对聚合反应的影响,并用红外光谱和核磁共振光谱对合成的聚乳酸进行了表征.

Polylactic acid was synthesized from commercial available cheap aqueous lactic acid （85 wt% 90 wt% ） using succinic anhydride and SnCl2·2H2O as catalyst in the absence of organic solvents. As a result, polylactic acid with a molecular weight of 6× 10^4 was prepared in 10 h. The effect of the amount of catalyst used, reaction temperature, and reaction time on the polymerization were investigated in detail. The amount of catalyst is the main factor that effecting the polymerization. The yields and molecular weights of the PLA obtained by succinic anhydride increase with the amount of succinic anhydride used in the range of 0 to 0.07 wt %. The trend is changed to decrease when the amount of the catalyst exceeds 0.07 wt %. The optimum amount of succinc anhydride is about 0.07 wt %, considering high Mw and high yield. The reaction time is another factor that effecting the polymerization. In a period of 0- 10 h, the yield and molecular weight increase with the reaction time. In the longer reaction time that exceeds 10 h, the yields and molecular weights decrease with the time. The molecular weight of PLA reach a maximum after the reaction has been carried out for about 10 h. Polylactic acid obtained by succinic anhydride and SnCl2·2H2O was characterized by IR and NMR. This is a new catalytic system for the direct polymerization of the lactic acid. The catalyst is commercially available and used as received without further treatment. The monomer we used is cheap and renewable aqueous lactic acid. The new procedure is much simple, cheap and environmentally benign compared to those of the reported ones. This kind of polymer might be useful in biomedical applications.