聚酯催化缩聚与热降解过程的半经验量子化学研究

Study on the Mechanism of Catalyzed Polycondensation and Degradation of Polyester with Semiempirical PM3 Method

以苯甲酸β-羟乙酯(BAHET)为模型反应物,采用半经验量子化学方法(PM3),分析了生成聚酯的催化缩聚与热降解机理。计算结果表明,端羟基氧与酯羰基氧是反应物与金属催化剂作用的活性位。金属催化剂与两者作用后,可以使酯羰基碳的正电性与端羟基氧的负电性增加。由于静电作用力增加,促使缩聚反应得以进行。研究结果表明,在钛系催化体系中,端羟基氧和酯醚键氧能与钛原子作用形成热力学稳定的五元环结构,它的存在将影响钛系催化体系中聚酯的热降解行为。

Semiempirical method PM3 was firstly applied to study the mechanism of polycondensation and thermal degradation of polyester. During the calculation, benzole acid 2-hydroxy-ethyl ester (BAHET) was used as amodel compound. The results indicate that metal ion coordinate with the oxygen atoms of ester carbonyl group and hydroxyl end group, then the change of positive charge of C atom of ester carbonyl group and negative charge of O atom of hydroxyl are favored. Furthermore, the reaction proceeds by the nucleophilic attack of hydroxyl end groups, upon the ester carbonyl group. While Ti compound is used as catalyst, energy favorable five-ring chelate structure can be formed. Results of calculation show that the degradation of polyester can be affected by the five ring chelate structure.