Process for producing ethylene/α-olefin copolymer

Claim 1

A process for producing an ethylene/α-olefin copolymer 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 not lower than 120° 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 hafnium compound represented by the general formula (1): wherein Cp 1 and Cp 2 are independently a substituted or unsubstituted cyclopentadienyl group; a substituted or unsubstituted indenyl group, or a substituted or unsubstituted fluorenyl group; R 1 is a substituted or unsubstituted lower alkylene group or a dialkylsilanediyl group, R 1 crosslinking Cp 1 and Cp 2 together; R 2 and R 3 are independently halogen atoms, the ionizing ionic compound (b) being a compound which is capable of changing the metallocene compound (a) into a cationic form; and the organoaluminum compound (c) being represented by the general formula (3): wherein R 4 , R 4 ′ and R 4 ″ 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 and lithium; and said anion is selected from the group consisting of tetrakis(p-tolyl)borate, tetrakis(m-tolyl)borate, tetrakis(2,4-dimethylphenyl)borate, tetrakis(3,5-dimethylphenyl)borate and tetrakis(pentafluorophenyl)borate.