Ethylene/1‐Hexene Copolymerization Kinetics and Microstructure of Copolymers Made with a Supported Metallocene Catalyst

Abstract

AbstractEthylene/1‐olefin copolymers made with supported metallocenes in slurry or gas‐phase polymerization are often less homogeneous than those made with the same unsupported metallocene in solution polymerization. In particular, their molecular weight distributions are broader, having polydispersities higher than two, and sometimes their chemical composition distributions may even be bimodal. In our previous publication, we developed a mathematical model to describe the polymerization kinetics and polymer microstructure of ethylene homopolymers made with a supported metallocene catalyst. In this article, we extended that model to also cover the copolymerization of ethylene and 1‐hexene with the same supported catalyst. The copolymerizations are performed in parallel semibatch reactors using a metallocene catalyst supported on an inorganic porous carrier. 1‐Hexene concentration and polymerization time are the factors changed to investigate this system. Modeling results show that, as for the ethylene homopolymerization case, a three‐site model is needed to describe the molecular weight distributions of the copolymers, but their chemical compositions can be described with a single set of reactivity ratios. A single set of parameters is also enough to describe the copolymerization kinetics with this supported catalyst. A new method is also developed and tested to estimate reactivity ratios under composition drift in this article.