疏水性离子液体中脂肪族羟基酸的溶液缩聚反应研究

Due to the excellent biodegradability and biocompatibility, polyhydroxyalkanoates have been extensively applied in biomedicine, environment, food and other fields. In recent years, ionic liquids as non-volatile organic solvents play an important role in the green synthesis of a variety of organic compounds and new materials. Since the synthesis of aliphatic polyesters via conventional polycondensation is faced with the problems of high viscosity of polymer melt, high polymerization temperature, and difficulty of mass and heat transfer, we propose to design and synthesize bis(trifluoromethanesulfonyl)imide- and perfluoroalkanesulfonate-anionic hydrophobic ionic liquids. And the cationic structures are precisely engineered based on the solubility parameters, in order to realize homogeneous solution polycondensation of aliphatic hydroxy acids in the hydrophobic ionic liquids. Therefore, the viscosity of polymer melt and the polymerization temperature can be greatly reduced. Evaporation of small molecules from the polycondensations will be accelerated. Thus, side and reverse reactions of the polycondensations will be remarkably inhibited and high molecular weight polyhydroxyalkanoates can be synthesized in a greener manner. Solution polycondensation kinetics of aliphatic hydroxy acids in the hydrophobic ionic liquids will be further investigated. Interactions between ionic liquids and monomers, ionic liquids and catalysts, ionic liquids and polymers will be analyzed and discussed. Finally, we will propose reasonable polycondensation mechanism and find out the polycondensation principle of hydroxy acids in ionic liquids. This work is expected to provide theoretical foundation and database for chemical synthesis of high-performance biodegradable aliphatic polyesters.

脂肪族羟基酸聚酯因其优异的生物可降解性和生物相容性而被广泛用于医药、环境、食品等领域。近年来，离子液体作为不挥发有机溶剂在有机化合物和各类新材料的绿色合成中发挥重要作用。为了实现离子液体中脂肪族羟基酸的均相溶液缩聚，解决通过传统缩聚反应合成脂肪族聚酯所面临的聚合物熔体黏度和反应温度高，传质传热困难的问题，本项目拟设计合成以双三氟甲磺酰亚胺和全氟烷基磺酸根为阴离子的疏水性离子液体，并根据溶度参数相近原则精细调控离子液体阳离子结构，使离子液体与聚合物良好互溶，以此降低聚合物熔体黏度和反应温度，促进缩聚小分子的排出，减少可逆平衡缩聚的逆反应和高温副反应，合成高分子量脂肪族羟基酸聚酯。研究疏水性离子液体中羟基酸的缩聚反应动力学，探讨离子液体与催化剂、单体以及聚合物之间的相互作用，提出合理的反应机制，揭示离子液体中羟基酸的缩聚反应规律，为高性能生物可降解脂肪族聚酯的化学合成提供理论依据和数据支撑。

离子液体因其独特的物化性质在有机化合物和各类新材料的绿色合成中发挥着重要的作用，将离子液体作为“绿色溶剂”用于具有生物可降解性和生物相容性的脂肪族聚酯的合成可以解决传统熔融缩聚由于传质传热困难而导致的产品质量问题。本项目合成了14种结构和性质特异的疏水性离子液体，通过核磁共振波谱和热失重分析表征了离子液体的结构和性质，发现离子液体的溶度参数随着烷基碳原子数量的增加而降低。将所得疏水性离子液体用于脂肪族羟基酸的溶液缩聚反应体系，通过改变单体和催化剂浓度、反应温度和真空度、反应时间等反应条件，系统地研究了聚合反应速率、聚合物结构和分子量（分布）的影响因素。脂肪族羟基酸在离子液体中的缩聚反应可以降低反应温度和反应后期体系黏度，减少可逆平衡缩聚的副反应和逆反应，从而得到了明显高于传统熔融缩聚的聚合物分子量。进一步研究了L-乳酸在疏水性离子液体中的缩聚反应动力学，发现离子液体能加速反应进行，表现出一定的催化活性，但只有外加催化剂时才能有效提高聚合反应速率，获得高分子量脂肪族聚酯。通过计算缩聚反应速率常数、反应活化能，对比传统缩聚反应体系，获得了疏水性离子液体中脂肪族羟基酸缩聚反应的一般规律。