A process for polymerizing propylene in the presence of a polymerization catalyst comprising a solid catalyst component comprising a magnesium halide, a titanium halide and an internal electron donor; and a cocatalyst comprising an aluminium alkyl and optionally an external electron donor, said process comprising the steps of: continuously copolymerizing propylene by introducing streams of propylene, a comonomer selected from the group of ethylene and C4-C10 alpha-olefins, hydrogen and said polymerization catalyst into a loop reactor at a temperature of from 65 to 100 °C and a pressure of from 25 to 100 bar to produce slurry of particles of a first copolymer of propylene having a melt flow rate MFR 2 of from 0.3 to 3.0 g/10 min and a content of comonomer units of from 0.1 to 6 mol-% in a first reaction mixture; withdrawing a slurry stream from said loop reactor, said slurry stream comprising said particles of the first copolymer of propylene, said particles further comprising said polymerization catalyst, and passing the slurry stream into a gas phase reactor; continuously copolymerizing propylene by introducing streams of propylene, a comonomer selected from the group of ethylene and C4-C10 alpha-olefins and optionally hydrogen into said gas phase reactor at a temperature of from 65 to 100 °C and a pressure of from 10 to 40 bar to produce particles comprising a copolymer mixture of said first copolymer of propylene and a second copolymer of propylene, said copolymer mixture having a content of comonomer units from 2 to 12 mol-% and a melt flow rate MFR 2 of 0.05 to 0.4 g/10 min; wherein said copolymer mixture comprises from 30 to 60 % by weight of said first copolymer and from 40 to 70 % by weight of said second copolymer, and wherein the melt flow rate MFR 2 of said copolymer mixture is lower than the melt flow rate MFR 2 of said first copolymer and the content of comonomer units in said copolymer mixture is higher than the content of comonomer units in said first copolymer; withdrawing a stream comprising said copolymer mixture from said gas phase reactor; removing hydrocarbons from said stream to produce a polymer stream with reduced content of hydrocarbons and optionally introducing additives to the copolymer mixture; extruding said copolymer mixture into pellets. continuously copolymerizing propylene by introducing streams of propylene, a comonomer selected from the group of ethylene and C4-C10 alpha-olefins, hydrogen and said polymerization catalyst into a loop reactor at a temperature of from 65 to 100 °C and a pressure of from 25 to 100 bar to produce slurry of particles of a first copolymer of propylene having a melt flow rate MFR 2 of from 0.3 to 3.0 g/10 min and a content of comonomer units of from 0.1 to 6 mol-% in a first reaction mixture; withdrawing a slurry stream from said loop reactor, said slurry stream comprising said particles of the first copolymer of propylene, said particles further comprising said polymerization catalyst, and passing the slurry stream into a gas phase reactor; continuously copolymerizing propylene by introducing streams of propylene, a comonomer selected from the group of ethylene and C4-C10 alpha-olefins and optionally hydrogen into said gas phase reactor at a temperature of from 65 to 100 °C and a pressure of from 10 to 40 bar to produce particles comprising a copolymer mixture of said first copolymer of propylene and a second copolymer of propylene, said copolymer mixture having a content of comonomer units from 2 to 12 mol-% and a melt flow rate MFR 2 of 0.05 to 0.4 g/10 min; wherein said copolymer mixture comprises from 30 to 60 % by weight of said first copolymer and from 40 to 70 % by weight of said second copolymer, and wherein the melt flow rate MFR 2 of said copolymer mixture is lower than the melt flow rate MFR 2 of said first copolymer and the content of comonomer units in said copolymer mixture is higher than the content of comonomer units in said first copolymer; withdrawing a stream comprising said copolymer mixture from said gas phase reactor; removing hydrocarbons from said stream to produce a polymer stream with reduced content of hydrocarbons and optionally introducing additives to the copolymer mixture; extruding said copolymer mixture into pellets.