METHOD OF PREPARING ETHYLENE POLYMERS Russian patent published in 2001 - IPC

FIELD: chemistry of polymers. SUBSTANCE: described is method of preparing ethylene polymers in the presence of catalyst system consisting of ethylenically polymerizable catalyst and cocatalyst in multistage reaction sequence consisting of liquid-phase and gas- phase polymerization including at least one continuous reaction sequence wherein in first stage ethylene and optionally hydrogen and comonomer are polymerized in reaction with circulation in low-boiling hydrocarbon in the presence of ethylenically polymerizable catalyst and cocatalyst at 75-100 C for at least 10 minutes, reaction mixture is then removed and polymer is admitted into final stage wherein polymerization occurs in gas-phase reactor in the presence of added ethylene and optionally hydrogen, comonomers and cocatalysts. In first stage residence time and reaction temperature are selected so that part of ethylene polymer prepared in reaction with circulation in first polymerization is 1-20% based on final product. Reaction mixture withdrawn from first stage is further admitted into second stage, polymerization continuous in reactor with circulation when adding ethylene, hydrogen and optionally inert hydrocarbon, comonomers and cocatalyst, residence time is at least 10 minutes; in reactor with circulation of said first polymerization, melt index of the resulting polymer is lower than melt index of the polymer prepared in reactor with circulation of second stage of polymerization reaction, ratio of molecular weight of ethylene polymer prepared in first polymerization stage varies from 0.25 to 5, and in first polymerization stage, polymerization conditions are selected so that melt index I₂ of the resulting ethylene polymer varies from 0.01 to 50, and in second polymerization stage, melt index varies I₂ from 10 to 2000. EFFECT: simplified process and improved quality of the desired product. 9 cl, 4 tbl