Effect of 1-hexene comonomer on polyethylene particle growth and copolymer chemical composition distribution

An investigation of the polymer particle growth characteristics and polymer molecular weight and composition distributions in ethylene homopolymerization and ethylene/1-hexene copolymerization has been carried out with a catalyst comprising a zirconocene and methylaluminoxane immobilized on a silica support. The presence of 1-hexene leads to higher productivity and easier fragmentation of the support during particle growth. Crystallization analysis fractionation and gel permeation chromatography analysis of ethylene/1-hexene copolymers prepared at different polymerization times reveals a broadening of the chemical composition distribution with increasing polymerization time as a result of the gradual formation of a relatively high-molecular-weight, ethylene-rich fraction. The results are indicative of significant monomer diffusion effects in both homopolymerization and copolymerization. (c) 2006 Wiley Periodicals, Inc.