MULTISTEP PROCESS FOR PREPARING HETEROPHASIC PROPYLENE COPOLYMERS

摘要

A multistage process comprising the step of polymerizing propylene in the presence the presence of a catalysts system, comprising one or more metallocene compound of formula (I): wherein M is an atom of a transition metal; p is an integer from 0 to 3, X, same or different, is a hydrogen atom, a halogen atom, or a hydrocarbon group; L is a divalent bridging R¹ and R², are C₁-C₂₀-alkyl radicals; T, equal to or different from each other, is a moiety of formula (IIb) or (IIa): wherein R³, R⁴, R⁵, R⁶, R⁷, R^3', R^4', R^5', R^6' and R^7', are hydrogen atoms or hydrocarbon groups; with the proviso that at least one among R³, R⁴, R⁵, R⁶, R⁷ is different from hydrogen; R¹¹ is a hydrogen atom or a hydrocarbon group; R⁸, R⁹ and R¹⁰, are hydrogen atoms or hydrocarbon groups; and further comprising the step of contacting, under polymerization conditions, in a gas phase, ethylene and one or more comonomers. Where the amount of the polymer obtained in the first step ranges from 5% by weight and 90% by weight, of the polymer obtained in the whole process.