Abstract: There is disclosed a process for producing a polyolefin which comprises polymerizing an olefin by the use of a catalyst comprising a specific transition metal compound, an aluminoxane and a specific magnesium compound or a catalyst comprising a specific transition metal compound, an aluminoxane, a specific magnesium compound and an organoaluminum compound. The use of the above process in polymerizing the olefin enables efficient stable production of a high molecular weight polyolefin improved in the powder morphology of the produced polymer, facilitated in the regulation of the molecular weight distribution and gifted with excellent particle shape.

Abstract: An olefin polymer is prepared by homopolymerizing an olefin or copolymerizing two different olefins or an olefin and another polymerizable unsaturated compound in the presence of a polymerization catalyst containing (A) a transition metal compound represented by the formula (I):CpML.sub.x-1 (I)wherein M is a metallic element of Groups 3 to 10 of the Periodic Table or a metallic element of the lanthanide series; Cp is a cyclic compound group having a cyclopentadienyl skeleton of 5 to 30 carbon atoms; L is R', OR', SR', SO.sub.3 R'N'R'R", PR'R", wherein R' and R" are each a C.sub.1-20 hydrocarbon group or a silyl group, NO.sub.2, a halogen atom, a 1-pyrrolyl group or a 1-pyrrolidinyl group, with the proviso that at least one of the L groups is OR', SR', N'R'R" or PR'R", wherein R' and R" are each a C.sub.

Abstract: A process for producing a polyolefin is here disclosed which comprises the step of polymerizing olefins in the presence of a catalyst comprising (A) a compound of a transition metal in the group IV of the Periodic Table, (B) an aluminoxane, (C) a compound having 2 or more aromatic rings in its molecule represented by the formulaAr.sup.1 --(YR.sub.n-2).sub.k --Ar.sup.2wherein the symbols are as defined in the specification, and if necessary, (D) an organic aluminum compound. In this process, the novel catalyst having a high polymerization activity is used, whereby the desired polyolefin can be efficiently produced.

Abstract: A process for the preparation of an ethylenic polymer composition having excellent physical properties such as high impact properties, environmental stress cracking resistance, pinch-off fusing characteristics and having an intrinsic viscosity ranging from 3.2 to 4.5 dl/g and a density ranging from 0.943 g/cm.sup.3 to 0.958 g/cm.sup.3.