GAS-PHASE PROCESS FOR PREPARING HETEROPHASIC PROPYLENE COPOLYMERS

摘要

A polymerization process for preparing heterophasic propylene copolymers in two or more gas-phase reactors connected in series, in the presence of a polymerization catalyst comprising a catalytic component based on a titanium compound supported on magnesium halide, the process comprising the following steps:-contacting said catalytic component with an organo-Aluminum compound at a temperature from 5°C to 30°C and a weight ratio propylene/(catalytic component) ranging from 0 to 2.0;-prepolymerizing the catalyst from A) with propylene, optionally in the presence of an inert hydrocarbon solvent;-polymerizing propylene, optionally with an another-olefin comonomer in an amount lower than 15% by weight, to prepare a semicrystalline polymer component;-successively copolymerizing two or more alpha-olefin comonomers C2-C10 to prepare one or more olefin copolymers having a solubility in xylene higher than 15% by weight; the process being characterized in that the bulk density of the semi-crystalline component of step C) is adjusted at a value lower than 0.40 g/cm3.