Comprehensive Investigation of Catalyst Structure and Polymerization Conditions for Chain Branching in Ethylene Polymerization with Phillips-Type Catalysts

Control factors of branching in ethylene polymerization on CrO(x)/SiO(2) catalysts were comprehensively investigated by varying catalyst structure and polymerization conditions. Variation of the polymerization conditions such as polymerization time, catalyst concentration, polymerization temperature, and alkylaluminum concentration indicated that the branch frequencies in produced polyethylene were highly relevant to the polymerization yield, plausibly through concentration of in-situ-produced alpha-olefins. A method to fairly compare the branching abilities of different catalysts was proposed. The application of the method to model catalysts with controlled chromium nuclearity proved an important role of dinuclear species in methyl branching through olefin metathesis.