Patent ID: 7365136

Claim:
A process for preparing linear high melt strength propylene homopolymers and copolymers, comprising the steps of subjecting propylene and optionally other olefins to polymerization in a plurality of polymerization reactors connected in series wherein said reactors are selected from the group consisting of loop reactors and gas phase reactors and wherein said reactors comprise at least one loop reactor and at least one gas phase reactor, employing different amounts of hydrogen as a molar mass modifier in at least two of the reactors, and carrying out the polymerization reaction in the presence of a catalyst system which catalyzes the formation of a high molar mass polymerization product having a MFR 2 of less than 0.1 g/10 min and a low or medium molar mass polymerization product having a MFR 2 of more than 0.5 g/10 min, wherein the second reactor is a gas phase reactor, wherein propylene and optionally comonomers are polymerized in a gaseous reaction medium and wherein (a) an overhead stream from a flash tank or part of it is recirculated to the first reactor or (b) an overhead stream or part of it from the second reactor is recirculated to the first and second reactor.