Two-State Models for Olefin Polymerization using Metallocene Catalysts. 1. Application to Fluxional Metallocene Catalyst Systems

Abstract

A kinetic model was developed to describe the propylene polymerization behavior of fluxional, two-state metallocene catalysts. In particular, the pentad and molecular weight distributions can be described as well as other parameters of interest, such as the weight fraction of crystallizable sequences and the isotactic sequence length distribution, in terms of fundamental kinetic constants and polymerization conditions that pertain to these two-state catalyst systems. The model was used in an attempt to describe the polymerization behavior of two, prototypical, fluxional catalyst systems, (2-PhInd)2ZrCl2/MAO (1) and (2-p-CF3PhInd)2ZrCl2/MAO (2). The model can accurately reproduce the pentad distributions observed in PP prepared using these catalysts and the response of the distribution to changes in polymerization conditions, specifically changes in [C3H6] at constant T. These studies illustrate that the rate of state-to-state interconversion is slower but of comparable magnitude to the rate of monomer ins...