Elastomeric propylene copolymers and process for manufacturing them in gas phase.

摘要

The present invention relates to elastomeric copolymers of propylene with ethylene and/or 1-butene and optionally with at least one C5-12 alpha-olefin, and to a process for manufacturing them in gas phase. The process employs a catalyst obtained by contacting a support successively with an electron-donor containing labile hydrogen D2 and with an electron-donor D3 chosen from aromatic carboxylic esters, and then by impregnating and activating the support by two successive contactings with titanium tetrachloride, the said support consisting of 80 to 99 mol% of magnesium dichloride and of 1 to 20 mol% of an organic electron-donor D1 free from labile hydrogen. The process comprises a stage of prepolymerisation by contacting the catalyst with at least one C2-12 alpha-olefin, an external electron-donor D4 and a cocatalyst (A).