Comonomer effects in copolymerization of ethylene and 1‐hexene with MgCl2‐supported Ziegler‐Natta catalysts: New evidences from active center concentration and molecular weight distribution

Abstract

ABSTRACTIn this article, comonomer effects in copolymerization of ethylene and 1‐hexene with four MgCl2‐supported Ziegler‐Natta catalysts using either ethylene or 1‐hexene as the main monomer were investigated. It was found that no matter which monomer was used as the main monomer, the polymerization activity was significantly enhanced by introducing small amount of comonomer. In copolymerization with ethylene as the main monomer, the strength of comonomer effects was much stronger in active centers producing low‐molecular‐weight polymer than those producing high‐molecular‐weight polymer. In copolymerization with 1‐hexene as the main monomer, the number of active centers ([C*]/[Ti]) was determined, and the propagation rate constants (kp) were calculated. Deconvolution of the polymer molecular weight distribution into Flory components were made to study the active center distribution. Introduction of small amount of ethylene caused marked increase in the number of active centers and decrease in average chain propagation rate constant. Introducing internal electron donor in the catalyst enhanced not only the number of active centers but also the chain propagation rate constant. In copolymerization of 1‐hexene with small amount of ethylene, the internal donor weakened the comonomer effects to some extent and changed the distribution of comonomer effects among different types of active centers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41264.