Mitsui Petrochemical Industries, Ltd.

Tomoko Sueyoshi

Masaaki Kawasaki

Masayuki Okabe

Kenji Wakatsuru

Atsuo Kobata

Yoshio Miyake

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. In an embodiment of the invention a polymer solution containing the resulting polyolefin obtained from the polymerization process is fed to a separation zone kept at a temperature of not lower than the upper cloud point of the polymer solution to separate the polymer solution into a lower phase portion containing the polyolefin in a high concentration and an upper phase portion, so as to recover the polyolefin from the lower phase portion in the separation zone and to recycle at least a part of the upper phase portion to the polymerization zone.

Process for the preparation of polyolefin

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. According to the invention, the steps for preparing cycloolefin random copolymer pellets can be reduced, and moreover, mold staining can De inhibited in the molding process of the resultant pellets because the pellets have low contents of the low molecular weight copolymer, the unreacted monomer, etc.

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Kuga, Japan

Tomoko Sueyoshi