LOW, MEDIUM AND HIGH DENSITY SINGLE-CATALYST POLYETHYLENES Russian patent published in 2010 - IPC C08F210/16 C08F4/642 

FIELD: chemistry.

SUBSTANCE: present invention relates to synthesis of medium and high density polyethylenes with a single catalyst composition. A method of polymerising ethylene and α-olefin is described, which involves mixing ethylene at partial pressure at least equal to 1300 kPa and optionally one or more α-olefins with a catalyst composition in a continuous polymerisation reactor at pressure blow 10000 kPa, in which the catalyst composition contains hafnocene; and extraction of polyethylene having density ranging from 0.930 to 0.975 g/cm³, and characterised by that when molar ratio of α-olefin to ethylene in the reactor ranges from 0 to 0.20, catalyst efficiency does not change by more than 30%. Also described is a method of converting the poly(ethylene/α-olefin) product in one reactor to a second poly(ethylene/α-olefin) product involving: (a) operation of the reactor at pressure below 10000 kPa with a first molar ratio hydrogen:ethylene and a first molar ratio comonomer: ethylene; (b) extraction of the first poly(ethylene/α-olefin) product; (c) varying one or both the first molar ratio of hydrogen to ethylene and the first molar ratio of comonomer to ethylene to obtain a second molar ratio of hydrogen to ethylene and a second molar ratio of comonomer to ethylene; and (d) extraction of the second poly(ethylene/α-olefin) product, in which the conversion is possible using the same catalyst composition, and in which density of the first poly(ethylene/α-olefin) product is less than or equal to 0.920 g/cm³ and density of the second poly(ethylene/α-olefin) product is greater than or equal to 0.935 g/cm³, or in which conversion is possible using the same catalyst composition which contains hafnocene, and in which I₂ of the first poly(ethylene/α-olefin) product is less than or equal to 8, measured according to ASTM D-1238E 190°C/2.16 kg and I₂ of the second poly(ethylene/α-olefin) product is more than or equal to 12, measured according to ASTM D-1238E 190°C/2.16 kg and characterised by that, when molar ratio of α-olefin to ethylene in the reactor ranges from 0 to 20, catalyst efficiency does not change by more than 30%.

EFFECT: obtaining medium and high density polyethylenes.

27 cl, 4 dwg, 6 tbl, 20 ex