Effect of Prepolymerization and Hydrogen Pressure on the Microstructure of Ethylene/1-Hexene Copolymers Made with MgCl2-Supported TiCl3 Catalysts

Abstract

The effect of prepolymerization and hydrogen pressure on ethylene/1-hexene copolymerization was investigated with two catalysts having different Ti3+ structure, i.e., isolated Ti3+ and multinuclear Ti3+ species. After prepolymerization with 1-hexene under mild conditions in the absence of hydrogen, the polymerization rates of both catalysts were enhanced. However, in the presence of hydrogen, both catalysts showed a decrease in the polymerization rate. From microstructure analyses with carbon-13 nuclear magnetic resonance (C-13-NMR), gel permeation chromatography and crystallization analysis fractionation, prepolymerization for both catalysts increased the reactivity of 1-hexene and changed the short chain branching distribution (SCBD) of the produced polymer but did not alter the molecular weight distribution (MWD). In the presence of hydrogen, isolated Ti3+ species showed a remarkable increase in the 1-hexene reactivity and produced copolymers having broad MWDs and SCBDs. Multinuclear Ti3+ species did not show significant changes in 1-hexene reactivity and SCBD of the produced copolymer when exposed to hydrogen. (C) 1999 Elsevier Science Ltd. All rights reserved.