Preparation of Ethylene-1-Hexene Copolymers with Bimodal Molecular Weight Distribution and Optimal Branching Distribution on a Highly Active Supported Vanadium-Magnesium Catalyst

Using a new modification of a highly active vanadium-magnesium catalyst (VMC), data were obtained on the effect of hydrogen and hexene-1 content on the catalyst activity and the molecular structure of the resulting polymers. It was found that the formation of polyethylene (PE) with a wide bimodal molecular weight distribution (MWD) on VMC is associated with the presence of two groups of active centers in these catalysts, differing in their reactivity in the polymer chain transfer reaction with hydrogen. It was also found that the presence of hexene-1 during copolymerization leads to an additional broadening of the MWD of the copolymer due to a predominant decrease in the molecular weight of the copolymer in the low-molecular region. At the same time, the active centers of the VMC, producing a high-molecular polymer, practically do not participate in the chain transfer reaction with hexene-1. At the same time, these centers are more reactive in the reaction of insertion of hexene-1, which leads to an increased content of butyl branches in the high-molecular fraction of the copolymers. The kinetic features of highly active VMCs found indicate their promise for the production of pipe and film grades of PE using a one-reactor scheme instead of a two-reactor scheme used to produce bimodal PE on traditional titanium-magnesium catalysts.

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