METHOD FOR PREPARING COMPOSITION OF LINEAR LOW DENSITY POLYETHYLENE Russian patent published in 2006 - IPC C08F297/08 G01L23/08 C08J5/18 

FIELD: organic chemistry, polymers, chemical technology.

SUBSTANCE: invention relates to a method for synthesis of bimodal compositions of linear low density polyethylene, films made of its and showing the improved balance of mechanical properties and technological effectiveness. Invention describes a method for synthesis of bimodal ethylene copolymers of low density useful for making films. Method involves the following steps: carrying out the first polymerization reaction or co-polymerization of ethylene, hydrogen and co-monomers chosen from (C₃-C₁₈)-olefins in the presence of Ziegler-Natt catalyst in the first reaction zone in circulation reactor for synthesis of the first polymerization product with low molecular mass, the flow rate of melt CTP₂ from 50 to 500 g/10 min but preferably from 100 to 400 g/10 min, and density value from 940 to 955 kg/m³ but preferably from 945 to 953 kg/m³; isolation of the first polymerization product from the first reaction zone; charge of the first polymerization product to the second reaction zone in gas-phase reactor; charge of additional ethylene, co-monomers chosen from (C₃-C₁₈)-olefins and, possibly, hydrogen to the second reaction zone; carrying out the second polymerization reaction for preparing polymeric composition comprising from 41 to 48 wt.-% of low-molecular polymer and from 52 to 59 wt.-% of high-molecular polymer; bimodal low-density ethylene copolymer has the flow rate of melt in the range of CTP₂ from 0.4 to 1.0 g/10 min but preferably from 0.4 to 0.7 g/10 min and density value from 918 to 925 kg/m³. Then method involves isolation of the combined polymerization product from the second zone of reaction. Also, invention describes film and method for its making. Prepared film shows good mechanical and optical properties and method provides the possibility for stable work for prolonged time intervals and without necessity of manufacture stop.

EFFECT: improved method of synthesis.

9 cl, 2 tbl, 7 ex