Propylenpolymersammensetning for et trykkløst polymerrør, trykkløst polymerrør, samt en fremgangsmåte for fremstilling av polymersammensetningen

A pressureless polymer pipe, a composition therefore, and a process of preparing the composition are described. The pipe is characterised in that the polymer comprises a propylene polymer composition where the propylene base polymer is a heterophasic propylene copolymer having a matrix of a propylene homopolymer and a dispersed phase of an elastomeric copolymer of propylene and at least one olefin comonomer; has a comonomer content of 2-7 % by weight, based on the weight of the heterophasic propylene copolymer; has a melt flow rate MFR (2/230), determined according to ISO 1133 C4, of 0.1-2.0 g/10 min; has a broad molecular weight distribution as defined by its rheology shear thinning index, SHI 0/50 , measured at 200°C of 9-30; has a tensile modulus, determined according to ISO 527-2/1B at 1 mm/min and 23°C of at least 1800 MPa; has an impact strength, determined according to ISO 179/1eA of at least 6 kJ/m 2 at 0°C and at least 2 kJ/m 2 at -20°C. The composition is a polymer composition as defined above. The process is characterised by polymerizing in the presence of a stereospecific Ziegler-Natta catalyst including an electron donor: (i) a propylene homopolymer matrix in at least one loop reactor at a temperature of at least 80°C and a pressure of 4600-10000 kPa; and (ii) an elastomeric copolymer of propylene and at least one olefin comonomer in at least one gas-phase reactor at a lower temperature than in stage (i); €ƒ€ƒ€ƒ to obtain a base polymer of heterophasic propylene copolymer as defined above.