The Kinetic Study of Ethylene Polymerization over Titanium-Magnesium Catalysts in the Presence of Hydrogen: The Number and Reactivity of Active Centers

摘要

Using the inhibition of polymerization by radioactive carbon monoxide (CO)-C-14, the effect of hydrogen (chain transfer agent) on the number of active centers and propagation rate constant in ethylene polymerization over modern highly active titanium-magnesium catalysts with different composition is studied. It is found that a decrease in the rate of ethylene polymerization in the presence of hydrogen is associated primarily with reduction in the number of active centers and these changes are reversible at the introduction/removal of hydrogen. The scheme of reversible temporary deactivation of active center precursors is advanced to explain the experimental results. According to the data on the effect of hydrogen concentration on the molecular weight of polyethylene and the values of propagation rate constants, the rate constant of polymer chain transfer by hydrogen is calculated for catalysts with different composition.