The multiple-site nature of ethylene polymerization catalysts based on zirconyl carboxylates

Abstract

Zirconyl carboxylates in combination with alkylaluminum chlorides were shown to be active catalysts for the reaction of ethylene polymerization. It was found that the molecular-mass distribution of ethylene oligomers depends considerably on the donor-acceptor properties of a modifier of the catalytic system. The optimal conditions for obtaining the C₄–C₈ and C₈–C₁₈ fractions of linear α-olefins with yields of 75–80%, respectively, were determined. Experimentally observed deviation of the composition of oligomerization products from the statistical distribution of the Schulz-Flory type is caused by the multistie character of the catalytic system used. Modifiers that provide the formation of catalytic centers with higher coordination unsaturation (type I) promote the selective formation of the C₄–C₈ fraction (95%). Modifiers capable of forming semilabile ligands (type II) lead to an increase in the yield of the middle, C₆–C₁₀ and C₈–C₁₈ fractions. Modifiers with stronger chelating properties (type III) direct the process toward the formation of macromonomers and polymers of ethylene.