Polypropylene-ultrahigh-molecular-weight-polyethylene compositions

1. A process for the preparation of a PP/UHMW-PE (Polypropylene-Ultrahigh-Molecular-Weight-Polyethylene) composition having:

a melting temperature Tm in the range of 125 to 150° C. (DSC, ISO 11357, Part 3),

a melt flow rate (MFR 2 ) of 0.15 to 0.60 g/10 min (2.16 kg, 230° C., ISO1133),

units derived from 1-hexene in an amount of at least 1.80 wt. %, and

a xylene soluble content (XS) according to ISO16152 of less than 5.0 wt. %, all weight percentages with respect to the total PP/UHMW-PE composition;

wherein the process comprises the steps of:

(a) introducing a stream of propylene and 1-hexene to a first reactor, so that the molar ratio of the feed rate of 1-hexene to the feed rate of propylene is from 2.0 to 4.0 mol/kmol; further introducing a stream of a catalyst system to the first reactor, whereby the catalyst system includes:

(i) a catalyst having the following structure;

wherein;

M is zirconium or hafnium;

each X independently is a sigma-donor ligand;

L is a bridge of formula -(ER 10 2 ) y -;

y is 1 or 2;

E is C or Si;

each R 10 is independently a C 1 -C 20 -hydrocarbyl group, tri(C 1 -C 20 alkyl)silyl group, C 6 -C 20 aryl group, C 7 -C 20 arylalkyl group or C 7 -C 20 alkylaryl group or L is an alkylene group;

R 1 are each independently the same or are different from each other and are a CH 2 -R 11 group, with R 11 being H or linear or branched C 1 -C 6 alkyl group, C 3 -C 8 cycloalkyl group, C 6 -C 10 aryl group;

R 3 , R 4 and R 5 are each independently the same or different from each other and are H or a linear or branched C 1 -C 6 alkyl group, C 7 -C 20 arylalkyl group, C 7 -C 20 alkylaryl group, or C 6 -C 20 aryl group with the proviso that if there are four or more R 3 , R 4 and R 5 groups different from H present in total, one or more of R 3 , R 4 and R 5 is other than tert butyl;

R 7 and R 8 are each independently the same or different from each other and are H, a CH 2 -R 12 group, with R 12 being H or linear or branched C 1 -C 6 alkyl group, SiR 13 3 , GeR 13 3 , OR 13 , SR 13 , NR 13 2 ,

wherein

R 13 is a linear or branched C 1 -C 6 alkyl group, C 7 -C 20 alkylaryl group and C 7 -C 20 arylalkyl group or C 6 -C 20 aryl group,

R 9 are each independently the same or different from each other and are H or a linear or branched C 1 -C 6 alkyl group; and

R 2 and R 6 all are H; and

(ii) a cocatalyst system comprising a boron containing cocatalyst and an aluminoxane cocatalyst;

(iii) polymerizing propylene and 1-hexene in the presence of the catalyst system in the first reactor to produce a first intermediate; withdrawing a product stream comprising the first intermediate from the first reactor;

transferring the stream comprising the first intermediate to a second reactor and further polymerizing propylene in the second reactor in the presence of the first intermediate by feeding further propylene, 1-hexene and hydrogen into the second reactor such that

the molar ratio of the concentration of hydrogen to the concentration of propylene is in the range of 0.1 to 0.8 mol/kmol; and further

the molar ratio of the concentration of 1-hexene to the concentration of propylene is in the range of 4.0 to 6.0 mol/kmol

thus yielding a second intermediate and withdrawing a stream comprising the second intermediate from the second reactor

(b) transferring at least a part of the stream comprising the second intermediate to a third reactor and further polymerizing ethylene in the presence of the second intermediate by introducing ethylene into the third reactor to yield the PP/UHMW-PE (Polypropylene-Ultrahigh-Molecular-Weight-Polyethylene) composition, whereby the molar ratio of the concentration of hydrogen to the concentration of ethylene is less than 500 mol/1.0×10 6 mol.

2. The process according to claim 1 , comprising comprises feeding no fresh catalyst system to the second nor the third reactor.

3. The process according to claim 1 , whereby the first intermediate has:

a melting temperature Tm in the range of 145 to 155° C. (DSC, ISO 11357, Part 3), and/or

an MFR 2 of 0.20 to 0.55 g/10 min (2.16 kg, 230° C., ISO1133), and/or

units derived from 1-hexene in an amount of at least 0.5 wt. %, and/or

units derived from 1-hexene in an amount of less than 2.5 wt. %, and/or

a XS measured according to ISO16152 of less than 11.0 wt. %, and/or

a XS measured according to ISO16152 of more than 7.5 wt. %.

4. The process according to claim 1 , whereby the second intermediate has:

an MFR 2 of 0.25 to 0.55 g/10 min (2.16 kg, 230° C., ISO1133), and/or

units derived from 1-hexene in an amount of at least 2.0 wt. %.

5. The process according to claim 1 , whereby the amount of the first intermediate in the second intermediate is from 41 to 49% by weight.

6. The process according to claim 1 , whereby the amount of the second intermediate in the PP/UHMW-PE (Polypropylene-Ultrahigh-Molecular-Weight-Polyethylene) composition is from 85 to 99.5% by weight.

7. The process according to claim 1 , whereby the ratio of the MFR 2 (second intermediate)/MFR 2 (final PP/UHMW-PE composition) is 1.25 to 2.00.

8. The process according to claim 1 , whereby the first reactor is a loop reactor and/or the second reactor is a gas phase reactor and/or the third reactor is a gas phase reactor.

9. The process according to claim 1 , whereby a prepolymerization precedes the first polymerization stage taking place in the first reactor.