Long chain branched propylene polymer composition

1. A process for producing a propylene polymer composition comprising a long chain branched propylene copolymer, wherein the propylene polymer composition has

a) a crystallization temperature Tc of less than 115° C., determined by DSC according to ISO 11357-3,

b) a melting temperature Tm of less than 155° C., determined by DSC according to ISO 11357-3,

c) a F39 melt strength of from 5.0 to less than 30.0 cN, determined following ISO 16790:2005, and

d) a V30 melting extensibility of more than 190 mm/s, determined following ISO 16790:2005,

wherein the process comprises the following steps:

a) Polymerizing propylene and comonomers selected from alpha-olefins having from 4 to 12 carbon atoms in the presence of a single site catalyst system to produce a propylene copolymer;

b) Recovering the propylene copolymer;

c) Extruding the propylene copolymer in the presence of a peroxide for introducing long chain branching into the propylene copolymer;

d) Recovering the propylene polymer composition.

2. The process according to claim 1 , wherein the single site catalyst system comprises

(i) a metallocene complex of formula (I):

wherein

M is Zr or Hf

each X independently is a sigma-donor ligand,

L is a divalent bridge selected from —R′ 2 C—, —R′ 2 C—CR′ 2 —, —R′ 2 Si—, —R′ 2 Si—SiR′ 2 —, —R′ 2 Ge—, wherein each R′ is independently a hydrogen atom or a C 1 -C 20 -hydrocarbyl group optionally containing one or more heteroatoms of Group 14-16 of the periodic table or fluorine atoms, or optionally two R′ groups taken together can form a ring,

each R 1 are independently the same or can be different and are hydrogen, a linear or branched C 1 -C 6 -alkyl group, a C 7-20 -arylalkyl, C 7-20 -alkylaryl group or C 6-20 -aryl group or an OY group, wherein Y is a C 1-10 -hydrocarbyl group, and optionally two adjacent R 1 groups can be part of a ring including the phenyl carbons to which they are bonded,

each R 2 independently are the same or can be different and are a CH 2 —R 8 group, with R 8 being H or linear or branched C 1-6 -alkyl group, C 3-8 -cycloalkyl group, C 6-10 -aryl group,

R 3 is a linear or branched C 1 -C 6 -alkyl group, C 7-20 -arylalkyl, C 7-20 -alkylaryl group or C 6 -C 20 -aryl group,

R 4 is a C(R 9 ) 3 group, with R 9 being a linear or branched C 1 -C 6 -alkyl group,

R 5 is hydrogen or an aliphatic C 1 -C 20 -hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16 of the periodic table of elements;

R 6 is hydrogen or an aliphatic C 1 -C 20 -hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16 of the periodic table of elements; or

R 5 and R 6 can be joined as part of a 5-membered ring condensed with the indenyl, which is optionally substituted by n groups R 10 , n being from 0 to 4;

each R 10 is same or different and may be a C 1 -C 20 -hydrocarbyl group, or a C 1 -C 20 -hydrocarbyl radical optionally containing one or more heteroatoms belonging to groups 14-16 of the periodic table of elements;

R 7 is H or a linear or branched C 1 -C 6 -alkyl group or an aryl or heteroaryl group having 6 to 20 carbon atoms optionally substituted by one to three groups R 11 ,

each R 11 are independently the same or can be different and are hydrogen, a linear or branched C 1 -C 6 -alkyl group, a C 7-20 -arylalkyl, C 7-20 -alkylaryl group or C 6-20 -aryl group or an OY group, wherein Y is a C 1-10 -hydrocarbyl group,

(ii) a cocatalyst system comprising an aluminoxane cocatalyst, and

(iii) a silica support.

3. The process according to claim 1 , wherein the amount of comonomer units in the polymerization step a) is from more than 0.5 wt % to 10.0 wt %, based on the total amount of monomer units in the propylene copolymer, determined by quantitative 13 C-NMR spectroscopy.

4. The process according to claim 1 , wherein the particles of the recovered propylene copolymer have a porosity of less than 10.0%, and/or a specific pore volume of less than 0.12 cm 3 /g, determined by mercury porosimetry according to DIN 661133 in combination with helium density measurement according to DIN 66137-2.

5. The process according to claim 1 , wherein the particles of the recovered propylene copolymer has a median particle size d50 of from 150 to 1000 μm, determined by sieve analysis according to ISO 3310.

6. The process according to claim 1 , wherein the propylene copolymer and the peroxide are melt mixed in a melt mixing device at a barrel temperature in the range of 160 to 280° C.

7. The process according to claim 1 , wherein the peroxide has a half-time (t 1/2 ) of not more than 6 min at a melt temperature of 160 to 280° C. and/or the peroxide is added to the propylene copolymer in an amount of 0.40 to 4.00 parts per weight (ppw) of peroxide per 100 parts per weight of propylene copolymer.

8. The process according to claim 1 , wherein the long chain branching is introduced into the propylene copolymer in the absence of a bifunctional long chain branching agent.

9. The process according to claim 1 , wherein the recovered propylene polymer composition of process step d) has a lower melt flow rate MFR 2 (230° C., 2.16 kg) compared to the recovered propylene polymer of process step b).

10. An article comprising the propylene polymer composition produced according to the process according to claim 1 .