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Abstract

A continuous process for obtaining propylene polymers in the presence of a catalytic system of the Ziegler-Natta type containing a catalytic solid comprising chlorine, magnesium and titanium atoms and at least one electron-donor compound, called internal donor, a cocatalyst which is an organoaluminium compound, and optionally an electron-donor compound, called external donor, comprising the following successive stages: (a) polymerization of propylene in liquid propylene to form, per g of titanium in the catalytic solid, from 11000 to 28000 g of a prepolymer chosen from among the homopolymers of propylene, and (b) gas-phase polymerization of propylene in one or more successive fluidized-bed reactors and in the presence of the prepolymer (a), of propylene, optionally in the presence of one or more other monomers chosen from among the .alpha.-olefins containing from 2 to 12 carbon atoms to produce a final propylene polymer whose fraction of particles of diameter smaller than 125 .mu.m (FP) is at most 10 wt %. A process for initiation of a continuous process for obtaining propylene polymers, comprising a stage of polymerization of propylene in liquid propylene end a stage of gas-phase polymerization in one or more successive fluidized-bed reactors and in the presence of the polymer obtained from the first stage, wherein the gas-phase polymerization reactor or reactors do not contain polymer particles in suspension.

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First Claim