A multilayer pipe of propylene plastic, wherein the pipe has a resistance to rapid crack propagation expressed as the critical temperature of the pipe, which is equal to or lower than 0° C., the critical temperature for a pipe being the lowest temperature at which an axial crack initiated in the pipe propagates a distance in the pipe of at most 4 times the diameter of the pipe at a pressure difference between the inside and outside of the pipe of 0.5 MPa;
- and that at least one of the layers of the pipe comprises a polypropylene, which is selected from polypropylene A [and] or polypropylene B,
- polypropylene A being a polypropylene containing from 1.0 to 10.0% by weight of ethylene or C4-C10-α-olefin repeating units and having an MFR2 value of between 0.05 and 0.40 g/10 min, and being obtained by polymerising propylene and ethylene or a C4-C10-α-olefin in the presence of a catalyst system, the procatalyst component of which is a reaction product of at least a tetravalent titanium compound and a magnesium halide compound and the cocatalyst component of which comprises an organoaluminium compound, optionally an external donor and hydrogen as a molecular weight regulating agent, to give said polypropylene, wherein the process for the preparation of said polypropylene comprises the following steps in any mutual order:
- (a) copolymerising propylene and comonomer into a random copolymer at 40 to 110° C. using:
- a catalyst system of the above-mentioned type;
- propylene;
- a portion of ethylene or C4-C10 -α-olefin comonomer leading to 1.0 to 10.0% by weight of ethylene or C4-C01-α-olefin repeating units in said random copolymer;
- and no or a minimal amount of hydrogen leading to an MFR10 value of between 0.01 and 5.0 g/10 min for said random copolymer, if this step is performed first, or to an MFR2 value for said polypropylene of between 0.05 and 0.40 g/10 min, if this step is performed after step (b);
- the proportion of random polymer produced in this step being from 20 to 80% by weight of said polypropylene A,
- (b) polymerising propylene at 40 to 100° C. using:
- a catalyst system of the above-mentioned type;
- propylene;
- no or a minimal portion of ethylene or C4-C10-α-olefin comonomer leading to 0.0 to 1.0% by weight of ethylene or C4-C10-α-olefin comonomer repeating units in the polymer produced in this step;
- and an amount of hydrogen leading to an MFR2 value of between 20 and 1000 g/10 min for said polymer, if this step is performed first, or to an MFR2 value for said polypropylene A of between 0.05 and 0.40 g/10 min, if this step is performed after step (a);
- the proportion of polymer produced in this step being from 80 to 20% by weight of said polypropylene A;
- and
- polypropylene B being an elastomer-modified polypropylene containing from 1.0 to 30% by weight of ethylene or C4-C10-α-olefin repeating units and having an MFR2 value of between 0.05 and 50 g/10 min, and being obtained by polymerising propylene and ethylene or a C4-C10-α-olefin in the presence of a catalyst system, the procatalyst component of which is a reaction product of at least a tetravalent titanium compound and a magnesium halide compound and the cocatalyst component of which comprises an organoaluminium compound, and hydrogen as a molecular weight regulating agent, as well as providing an elastomer component, to give said elastomer-modified polypropylene, wherein the process for the preparation of said polypropylene B comprises the following steps:
- (a) copolymerising propylene and comonomer into a random copolymer at 40 to 110° C. using:
- a catalyst system of the above-mentioned type;
- propylene;
- a portion of ethylene or C4-C10-α-olefin comonomer leading to 1.0 to 10.0% by weight of ethylene or C4-C10-α-olefin repeating units in said random copolymer;
- and no or a minimal amount of hydrogen leading to an MFR10 value of between 0.01 and 5.0 g/10 min for said random copolymer, if this step is performed first, or to an MFR2 value for said polypropylene B of between 0.05 and 50 g/l 0 min, if this step is performed after step (b);
- the proportion of random copolymer produced in this step being from 20 to 80% by weight,
- (b) polymerising propylene at 40 to 110° C. using:
- a catalyst system of the above-mentioned type;
- propylene;
- no or a minimal portion of ethylene or C4-C10-α-olefin comonomer leading to 0.0 to 1.0% by weight of ethylene or C4-C10-α-olefin comonomer repeating units in the polymer produced in this step;
- and an amount of hydrogen leading to an MFR2 value of between 20 and 1000 g/10 min for said polymer, if this step is performed first, or to an MFR2 value for said polypropylene B of between 0.05 and 50 g/10 min, if this step is performed after step (a);
- the proportion of the polymer produced in this step being from 80 to 20% by weight, and
- (c) providing a rubbery copolymer (elastomer), the proportion of which is from 5 to 40% by weight of said polypropylene, to give said elastomer-modified polypropylene.