Process for producing ethylene/α-olefin copolymer

A process for producing an ethylene/α-olefin copolymer of a weight-average molecular weight of not less than 40000 by copolymerization of ethylene with an α-olefin having three or more carbons by use of an olefin polymerization catalyst at a polymerization temperature of 120° C.-300° C.:

• the olefin polymerization catalyst comprising, a) a metallocene compound, b) an ionizing ionic compound and c) an organoaluminum compound:
• the metallocene compound (a) being a compound represented by the general formula Ph2C(Cp)(Flu)ZrCl2 wherein (Cp) is cyclopentadienyl, (Flu) is fluorenyl either unsubstituted or substituted (1) at at least one of the 2-7 positions by alkyl or aryl, or (2) at the 2,3 and 6,7 positions, or at the 1,2 and 7,8 positions, by benzene, the ionizing ionic compound (b) being a compound which is capable of changing the metallocene compound (a) into a cationic form and does not further react with the cationic form of the metallocene compound, and the organoaluminum compound (c) being represented by the general formula (2):
• wherein R5, R5′, and R5″ are independently an alkyl group,
• wherein said ionizing ionic compound is a salt of an anion and a cation;
• said cation is selected from the group consisting of tri(n-butyl)ammonium, N,N-dimethylanilinium, triphenylcarbenium, tropylium, lithium, sodium and potassium;
• said anion is tetrakis(pentafluorophenyl)borate, and;
• wherein the metallocene compound (a) and the organoaluminum compound (c) are present in a ratio of 100-10,000 moles of the organoaluminum compound per mole of the metallocene, and the ionizing ionic compound (b) and the metallocene compound (a) are present in a ratio of 0.1-100 moles of the ionizing ionic compound per mole of the metallocene, wherein said copolymerization is a solution polymerization at a polymerization pressure of from atmospheric pressure to 200 kg/cm2 or a high-pressure polymerization at a polymerization pressure of from 300 to 3500 kg/cm2, and wherein the amount of ethylene monomer is 33.2 to 81.0 mol % based on the amount of copolymer.