The present invention relates to a catalyst component for use in the polymerization or copolymerization of olefins. This catalyst component is high in catalytic efficiency, contains only a small amount of a modified organoaluminum compound, affords a polymer having a high molecular weight and a relatively wide molecular weight distribution, and permits easy control of the molecular weight and molecular weight distribution. The present invention is further concerned with a catalyst using the said catalyst component and an olefin polymer preparing process using such catalyst. The olefin polymer as referred to herein is a generic term for both homopolymer and copolymer of olefins.
As means for obtaining such an ethylenic polymer as polyethylene or ethylene/.alpha.-olefin copolymer having a narrow molecular weight distribution and a narrow composition distribution there recently has been proposed the use of a catalyst comprising a zirconium compound and an aluminoxane (JP58-19309A).
According to a process using such proposed catalyst there is obtained an ethylene copolymer in high yield which copolymer is narrow in both molecular weight distribution and composition distribution. However, the molecular weight of the copolymer is low and the amount of the aluminoxane used is large.
JP3-234005A proposes the use of a transition metal compound having a 2, 3 or 4-substituted cyclopentadienyl group to improve the molecular weight of the resulting polymer. In JP2-22307A it is proposed to use a hafnium compound having a ligand bonded to at least two crosslinked conjugated cycloalkadienyl groups for improving the molecular weight of the resulting polymer.
However, the use of hafnium as a transition metal is disadvantageous in that the yield of the resulting polymer is low.
It is the object of the present invention to provide a catalyst and process for preparing an olefin homopolymer or copolymer having a high molecular weight and a relatively wide molecular weight distribution in high yield using an extremely small amount of a modified organoaluminum compound (particularly methylaluminoxane).