熔融缩聚法合成可降解超支化聚乳酸

Synthesis of Degradable Hyperbranched Poly(lactic Acid) by Melt Polycondesation

以D,L-乳酸、葡萄糖酸和丙三醇或季戊四醇为原料,采用熔融缩聚法合成了具有超支化结构的聚乳酸(HPLA).用NMR、GPC、粘度计等测试手段对聚合物进行了表征,并证明了支化结构的存在.所合成的HPLA相对平均分子量较小.水解降解的结果表明随着超支化聚乳酸分子量的增加其水解速率呈减小趋势.DSC和TG表征的结果显示,超支化聚乳酸具有良好的热稳定性,分解温度高于230℃,其玻璃化转变温度较低,并且随着分子量的增加而升高.由于超支化结构的存在使得在合成过程中体系的粘度始终较低,因而整个合成反应速度明显要快于同催化剂催化合成LPLA时的反应速度.

Hyperbranched poly（lactic acid） （HPLA） was synthesized by using D, L-lactic acid, gluconic acid and glycerol or pentaerythritol as starting material by means of polycondensation. The branched structure of the polymer was confirmed by characterization with nuclear magnetic resonance, gel permeation chromatography and viscometry. The average molecular weight of synthesized hyperbranched PLA was small. The hydrolytic degradation of barbell-like copolymers in PBS was at 37 ℃ and the results demonstrated that the weight loss of samples decreased with increasing the molecular weight. The thermal properties were evalua- ted by using differential scanning calorimetry （DSC） and by performing a thermogravimetric analysis （TG）. The result indicated that the thermal properties of HPLA was stable under 230 ℃. The glass-transition temperature （Tg） was observed to decrease with the increase of branch-points. It was propitious to prepare poly（lactic acid） with higher molecular weight.