Ziegler-Natta配位聚合反应机理的量子化学研究——Cossee机理中活性中心的构型及其有关的关键步骤

本文采用ASED-MO理论对丙烯聚合的 Ziegler-Natta 催化过程的机理进行了理论研究。按照Cossee机理进行计算,得到了和实验事实基本一致的结果。认为该机理基本上是合理的,并对其中的关键步骤进行了理论解释,而对其中一些尚有争论的问题,如催化中心的稳定构型、丙烯分子和活性中心之间的配位作用、链增长过程和催化循环等问题提出了自己的见解。

QUANTUM STUDIES OF THE MECHANISM OF COORDINA- TION POLYMERIZATION WITH ZIELER-NATTA CATALIST

Up to now, on Cossee's mechanism, the stable configuration of catalytical centre, the essence of propylene coordination, the process of chain propagation, effect of alkyl aluminim and even whether Cossee's mechanismis resonale or not have still not come to identical understanding. In present paper, a theoritical study of the mechanism of propylene polymerization with Ziegler-Natta catalyst has been investigated in terms of the ASED-MO method. Acoording to Cossee's model, the calculated results are basically in agreement with the experimental, so it can be considered to be rational. Moreover, there is need to further investigate the related key reactions to clarify the details of mechanism. It is shown that the stable configuration of catalytical centre is a trigonal bipyrimid and it is activated by coordinating of propylene molecule, to be transformed into a octahedron. It is just a weak coordinated bond linked propylene and Ti3+ in active species has not effect of back-donated electrons. But coordinating propylene can change the charge distribution of system to facilitate the polymer chain propagation.The average activation energy of polymerization calculated is 59.2 KJ. Mol-1 and reaction enthalpy H is about 69.96 KJ.mol-1. For some disputed proplems, explanations are also given.