Abstract: A process for the preparation of polyolefin which comprises polymerizing or copolymerizing olefin in the presence of a catalyst for olefin polymerization comprising (A) a metallocene compound of a transition metal selected from the Group IVB of the periodic table, and (B) an organoaluminum oxy-compound; wherein the organoaluminum oxy-compound (B) is added to the polymerization system in the form of a slurry in an aliphatic hydrocarbon or alicyclic hydrocarbon, and the polymerization is carried out in the presence of the aliphatic hydrocarbon diluent or an alicyclic hydrocarbon diluent having a boiling point below 100.degree. C.

Abstract: Disclosed is a process for preparing cycloolefin random copolymer pellets, comprising adding an organic polar solvent to a solution of a copolymer obtained by copolymerizing ethylene and a specific cycloolefin and if desired an .alpha.-olefin other than ethylene, in an amount exceeding such an amount that the liquid mixture exhibits the cloud point, separating the copolymer solution utilizing phase separation phenomenon into a concentrated phase containing the cycloolefin random copolymer in a high concentration and a dilute phase containing said copolymer in a low concentration, feeding the obtained concentrated phase to an extruder where the solvents are removed and the copolymer is melted during extrusion processing, followed by pelletizing the copolymer.