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Abstract

A stable continuous production of a propylene-based block copolymer can proceed for a long time without causing accumulation of particles having a small diameter by a process having the following steps: (1) polymerizing an .alpha.-olefin containing liquid propylene as a main component in the presence of hydrogen and a stereoregular polymerization catalyst in one or more polymerization reactors to obtain a polymer slurry; (2) feeding the polymer slurry to a copolymerization reactor; and (3) copolymerizing propylene and an .alpha.-olefin other than propylene substantially in a gaseous phase in the presence of the stereoregular polymerization catalyst, the polymer slurry and a deactivating compound in the copolymerization reactor to obtain a propylene-block copolymer powder. The polymer slurry, discharged from one of said one or more polymerization reactors and is classified using a classification system to obtain a) a classified polymer slurry containing a large amount of particles having a small particle diameter and b) a classified polymer slurry containing a large amount of particles having a large particle diameter. A main part of the classified polymer slurry containing a large amount of particles having a small particle diameter is recycled to a final polymerization reactor of the one or more polymerization reactors.

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First Claim