生物降解材料聚L-乳酸的熔融缩聚合成

背景:通过对合成工艺和催化剂的优化和选择,合成较高相对分子质量的聚乳酸生物降解材料.方法:实验于2003-02/2004-10在哈尔滨工业大学市政环境工程学院绿色化学与技术研究中心完成.以L-乳酸为原料,通过熔融缩聚的一步法合成可生物降解的聚L-乳酸.乳酸首先在无催化剂存在条件下发生自催化缩聚反应,生成较低相对分子质量的预聚物OLLA;然后将催化剂加入到OLLA中继续反应,最后得到较高相对分子质量的聚乳酸.实验考察了预聚条件、催化剂种类和用量、催化剂溶解程度、聚合温度及反应时间对聚乳酸分子量的影响.采用傅立叶变换红外光谱仪和核磁共振氢谱对聚合物结构进行了分析确认,通过凝胶气相色谱测定了聚合物的相对分子质量分布.结果:L-乳酸在140 ℃下,先在30 kPa下脱水反应2 h;然后减压至5 kPa继续反应4 h,可得到黏均相对分子质量(Mη)为6 500左右的OLLA.以SnCl2-TSA复合体系为催化剂,按SnCl2与OLLA质量比= 0.4%,TSA:SnCl2=1.0(mol/mol)的用量和配比,将催化剂加入OLLA中并充分溶解后,在165 ℃左右,5 kPa下搅拌反应8 h左右,至反应物出现爬杆现象时终止反应,可得到Mη约为65 000的聚L-乳酸.结论:在优化的工艺条件和催化剂下,能够在较短时间(8 h)内获得较高相对分子质量的聚L-乳酸,使该生物降解材料具备了一定的实用价值.

Direct synthesis of biodegradable ploy L-lactic acid by melt polycondensation

AIM: To synthesize biodegradable poly lactic acid (PLA) through the optimization and selection of process and catalyst.METHODS: This experiment was performed at the Research Center for Green Chemistry and Technology in the School of Municipal and Environmental Engineering of Harbin Institute of Technology from February 2003 to October 2004. Biodegradable poly L-lactic acid (PLLA) was synthesis by melt polycondensation using L-lactic acid (LA) as material. Firstly, oligo L-lactic acid (OLLA) was prepared by dehydrating aqueous solution of LA without catalyst. And then, the mixture of OLLA and catalyst was heated at a certain temperature and pressure for a period of time to get the product of PLLA. The structure of PLLA was characterized by Fourier transform infrared (FTIR) spectra and 1H- nuclear magnetic resonance (1H-NMR) spectra. The polydispersity was determined by gel permeation chromatography (GPC).RESULTS: OLLA with the viscosity average molecular weight (Mη) of 6 500 g/mol was prepared by the following steps: the solution of LA without catalyst was dehydrated at 140 ℃, first at reduced pressure of 30 kPa for 2 hours, and then at 5 kPa for 4 hours. SnCl2-p-toluenesulfonic acid (TSA) system was the effective catalyst for the polycondensation of OLLA. After the mixture of OLLA and catalysts polycondensed at 165 ℃ and 5 kPA for about 8 hours, PLLA with the Mη of 65 000 g/mol was obtained by using SnCl2-TSA system as catalyst with the SnCl2 amount of 0.4wt% to OLLA and equal mol ratio of SnCl2 and TSA.CONCLUSION:PLLA with a certain practicability was obtained under the optimal process and catalyst. Oligomerization of LA played an important role on improving the molecular weight of PLLA.