Heterophasic copolymer obtained by a process for producing heterophasic copolymer
A heterophasic copolymer composition obtained by a process comprising polymerising in multiple steps and multiple polymerisation reactors propylene monomer and a comonomer selected from ethylene, alpha-olefins having 4 to 10 carbon atoms and their mixtures, in the presence of an olefin polymerisation catalyst comprising a solid catalyst component and a co-catalyst, wherein the solid catalyst component comprises titanium, magnesium, halogen and an internal donor of the formula (I): wherein R 1 and R 2 are the same or different being a linear or branched C 1 -C 12 -alkyl group and R is hydrogen or a linear, branched or cyclic C 1 to C 12 -alkyl.
1. A heterophasic copolymer of propylene obtained by a process for producing a heterophasic copolymer comprising propylene monomer and a comonomer selected from ethylene, alpha-olefins having 4 to 10 carbon atoms and their mixtures, in the presence of an olefin polymerisation catalyst that comprises a solid catalyst component and a cocatalyst, wherein the solid catalyst component comprises titanium, magnesium, halogen and an internal donor,
the process comprising the steps of:
(1) introducing streams of the solid catalyst component, the cocatalyst, propylene monomer, hydrogen and optionally comonomer into a first polymerisation reactor;
(2) producing a first polymer of propylene in the first polymerisation reactor, the first polymer of propylene having a first melt flow rate MFR 2 of from 0.1 to 4.0 g/10 min;
(3) withdrawing a stream comprising the first polymer of propylene from the first polymerisation reactor and passing it to a second polymerisation reactor;
(4) introducing streams of propylene monomer and optionally hydrogen and comonomer into the second polymerisation reactor;
(5) producing a first polymer mixture comprising the first polymer of propylene and a second polymer of propylene in the second polymerisation reactor, the first polymer mixture having a second melt flow rate MFR 2 of from 0.05 to 2.0 g/10 min and which second melt flow rate is less than the first melt flow rate;
(6) withdrawing a stream comprising the first polymer mixture from the second polymerisation reactor and passing it to a third polymerisation reactor;
(7) introducing streams of propylene monomer and the comonomer into the third polymerisation reactor;
(8) producing the heterophasic copolymer comprising the first polymer mixture and a third copolymer of propylene in the third polymerisation reactor; wherein the amount of xylene soluble fraction in the heterophasic copolymer determined according to ISO 16152 is from 14 to 35% by weight and intrinsic viscosity measured from the amorphous polymer (AM) of the heterophasic copolymer is from 1.5 to 4.4 dl/g; and
(9) recovering the heterophasic copolymer from the third polymerisation reactor;
wherein the internal donor is a compound having the structure according to formula
and wherein R1 and R2 are the same or different being a linear or branched C1-C12-alkyl group and R is hydrogen or a linear, branched, or cyclic Cl to C12-alkyl;
said heterophasic copolymer comprising from 5 to 25% by mole of units derived from the comonomer and from 75 to 95% by mole of propylene units and a melt index MFR 2 of from 0.05 to 2.0 g/10 min.
2. A pipe made of heterophasic copolymer of propylene according to claim 1 .