A Proposed Mechanism for Olefin Polymerization, 2. EHMO and MM2 Study

Abstract

This paper reports the results about the model presented in Part 1 for olefin polymerization with metallocenes, using semiempirical extended Huckel molecular orbital (EHMO) and MM2 methods The main aspects of the model are analyzed. These are bipyramidal or octahedral coordination, two different olefins coordination and the possibility of different active sites. A model of polymerization for a C 2 catalyst, prototypical and with steric hindrance, and for a C s catalyst was analyzed with MM2 to evaluate steric effects. The electronic effects were modeled using MAO to determine the feasibility of the model. Models for ethylene and propylene coordination and insertion were considered. The insertion models were only of qualitative value and they were designed to evaluate the effect of a triggering second olefin. A third olefin coordination (polymerizable or not) was considered for C 2 and C s catalysts. Experimental evidence was analyzed with the different aspects of the model.