L-乳酸低聚物的异氰酸酯扩链反应工艺研究

采用直接熔融缩聚法制备L-乳酸低聚物。在氮气氛围下,使用六亚甲基二异氰酸酯(HDI)、二苯基甲烷二异氰酸酯(MDI)作扩链剂,研究了反应时间、温度、反应官能团配比、低聚物粘均相对分子质量(Mη)等对扩链反应的影响,对扩链产物进行了红外光谱表征及差示扫描量热分析。结果表明:HDI和MDI对L-乳酸低聚物均有较好的扩链效果,扩链反应规律基本相同;HDI的扩链效果优于MDI,扩链反应速率快,扩链时间短,扩链产物Mη高、熔点高、热性能好;较佳扩链反应工艺参数:nNOC∶nOH为1:1,反应温度165℃,HDI扩链时间20 min、MDI扩链时间30 min,L-乳酸低聚物M越高,扩链产物M越高。

Study on chain extension of L-lactic acid oligomer with isocyanate

The oligomer of L-lactic acid was prepared by directly melt polycondensation.The effects of reaction time and temperature,reactive group proportion,viscosity average realtive molecular mass ((-)M_η ) of the oligomer on the chain extension were studied with hexamethylene diisocyanate (HDI) and methylene diphenyl diisocyanate (MDI) as chain extender in nitrogen atmosphere.The chain extension products were characterized by infrared spectroscopy and analyzed by differential scanning calo-rimetry.The results showed that HDI and MDI both offered satisfying chain extension effect for L- lactic acid oligomer.Their chain extension reaction had the similar regularity.HDI was superior to MDI in the chain extension effect with the features of high reaction rate,short reaction time and the chain extension products with high (-)M_η,melting point and thermal properties.The reasonable chain extension process parameters were decided as followed; n_(N0C) : n_(OH) of 1:1,reaction temperature 165 ℃,HDI chain extension time 20 min,MDI chain extension time 30 min.The higher (-)M_η of L- lactic acid oligomer was,the higher (-)M_η of the chain extension product was.