Chisso Corporation

Takehiro Umeno

Hiroshi Shimizu

Nobutoshi Komori

Takeshi Suzuki

Atsuyoshi Shimizu

A process for producing ethylene-propylene block copolymer by the use of a catalyst employed for producing isotactic polypropylene is provided. This process is characterized in that a gas phase polymerization of propylene is substantially carried out in the presence of the catalyst obtained by combining a titanium trichloride composition with an average particle size of 10.about.100 .mu. and an organic aluminum to form the propylene polymer segment with a specific surface area more than 0.015 m.sup.2 /g at a yield of more than 3,000 g per 1 g of the titanium trichloride composition in the first step, and then a gas phase polymerization of a mixture of polypropylene and ethylene is successively carried out in the second step to form the copolymer segment with a copolymerization ratio of propylene:ethylene being 5.about.80 weight %:95.about.20 weight %, wherein the polymerized amount of the second step is 10-40% of total polymerized amount and wherein normal hexane extraction ratio (75.degree. C., 1 hour) of the ethylene-propylene block copolymer powders obtained is 1.about.10 weight %. The process of the present invention is one having an extremely high productivity industrially, and the modified polypropylene obtained has a superior low-temperature-impact strength and brittle temperature.

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Ichiharashi, Japan

Takehiro Umeno