Abstract: A polymerization catalyst comprising a reaction product of an organic rare earth metal compound of the formula (I),Cp.sub.a Lx.sub.b M.sub.c D.sub.d (I)(wherein in the formula (I), Cp is a substituted or unsubstituted cyclopentadienyl group, indenyl group, fluorenyl group or their derivatives, or a multidentate coordination compound residue obtained by bonding these groups by way of hydrocarbon or silicon,L is a metal selected from the group consisting of elements having an atomic number of 39 and 57-71,X is a halogen atom,M is an alkaline metal or alkaline earth metal,D is an electron donor,a is 1-2,b is 1-2,c is 0-1, andd is 0-3) with a Grignard reagent of the formula (II),RMgX (II)wherein in the formula (II), R is a hydrocarbon group, and X is a halogen atom); a method for producing a polyolefin or an olefin block copolymer by using the above-mentioned catalyst; and an olefin block copolymer produced by the above-mentioned method.

Abstract: The invention relates to a method for producing an ethylenic polymer composition, suitable for molding, at high catalytic efficiency. The ethylenic polymer composition produced has as a high melt tension when melted, and a high melt modulus (die swell ratio). The process comprises a three step polymerization of an olefin employing a transition metal catalyst, the catalyst being produced in a specific manner.