Process for producing heterophasic copolymers of propylene

Abstract

The present invention provides a process for producing a heterophasic copolymer composition. The polymerisation is conducted in the presence of an olefin polymerisation catalyst comprising a solid catalyst component further comprising titanium, magnesium, halogen and an internal donor, and a cocatalyst, the process comprising the steps of: (1) introducing streams of the solid catalyst component, the cocatalyst, propylene monomer and hydrogen 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 2.0 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 a stream of propylene monomer 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 MFR2 of from 0.05 to 1.0 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 composition comprising the first polymer mixture and a third copolymer of propylene in the third polymerisation reactor, the heterophasic copolymer composition having a third melt flow rate MFR2 of from 0.05 to 1.0 g/10 min, said heterophasic copolymer having a content of comonomer units of from 5 to 25% by mole; 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 composition from the third polymerisation reactor; characterised in that the internal donor is a compound having the structure according to formula (I); 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 C1 to C12-alkyl.

Dependencies are inferred from the claim text.