Process for preparing heterophasic propylene copolymers
Process for producing a heterophasic propylene copolymer using a specific class of metallocene complexes in a multistage polymerization process including a gas phase polymerization step. The invention further relates to the use of catalysts which comprise a specific class of metallocene complexes to produce a heterophasic propylene copolymer in a multistep process including a gas phase polymerization step.
1. A process for the preparation of a heterophasic propylene copolymer, the process comprising: preparing the heterophasic propylene copolymer in the presence of a single site catalyst comprising:
(i) a complex of formula (I):
wherein
M is zirconium or hafnium;
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 —, or —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;
R 1 and R 1′ are each independently hydrogen, C 5 -C 10 -aryl or a group —CH(R x ) 2 wherein each R x is independently H or a C 1-10 hydrocarbyl group, and optionally the two R x taken together can form a ring,
R 2 and R 2′ are each independently hydrogen, C 5 -C 10 -aryl or a group —C(R y ) 3 wherein each R y is independently H or a C 1-10 hydrocarbyl group, or optionally two or three R y groups taken together can form a ring,
whereby at least one of R 1 or R 2 and one of R 1′ or R 2′ is different from hydrogen, and
whereby R 2 together with one of R 1 , as well as R 2′ together with one of R 1′ may be part of a further mono- or multicyclic ring condensed to the phenyl ring,
R 3 and R 3′ are each independently a linear C 1 to C 6 hydrocarbyl group or a branched or cyclic C 4 to C 10 hydrocarbyl group, whereby the groups are not branched in α-position,
R 4 and R 4′ are each independently a tertiary C 4 to C 10 hydrocarbyl group,
R 5 and R 5′ are each independently a linear or branched C 1 to C 10 alkyl group or an C 5 -C 10 -aryl group, and
(ii) a cocatalyst comprising a compound of a group 13 metal,
the heterophasic propylene copolymer comprising:
(a-1) a matrix (M) that is a polypropylene homopolymer or propylene-ethylene random copolymer, and
(a-2) an elastomeric propylene-ethylene copolymer (E) dispersed in said matrix (M),
wherein the elastomeric propylene-ethylene copolymer (E) has:
(i) an intrinsic viscosity (IV) determined according to DIN ISO 1628/1 (in decalin at 135° C. in a range of from 3.1 to 8.0 dl/g,
(ii) an ethylene comonomer content in a range of from 10.0 to 80.0 wt %,
(iii) optionally a second comonomer selected from 1-butene in an amount of from 0.0 to up to 20.0 wt % or 1-hexene in an amount of from 0.0 up to 10.0 wt %, and
(iv) a xylene soluble (XS) fraction (determined according to ISO 16152 at 25° C.) of at least 50.0 wt %, and
wherein a xylene soluble fraction (determined according to ISO 16152 at 25° C.) of the heterophasic propylene copolymer is in a range of from 5.0 to 50.0 wt %.
2. The process according to claim 1 , wherein in the formula (I) each X is independently a hydrogen atom, a halogen atom, C 1-6 alkoxy group, C 1-6 alkyl, phenyl or benzyl group.
3. The process according to claim 1 , wherein in the formula (I) L is dimethylsilyl, methylcyclohexylsilyl (Me-Si-cyclohexyl), ethylene or methylene.
4. The process according to claim 1 , wherein in the formula (I):
R 3 and R 3′ are the same and are linear C 1 to C 4 alkyl group, and
R 4 and R 4′ are each independently a tertiary C 4 to C 6 alkyl group.
5. The process according to claim 1 , wherein in the formula (I):
M is zirconium,
X is independently a halogen atom, C 1-4 alkoxy group, C 1-4 alkyl, phenyl or benzyl group,
L is dimethylsilyl,
R 1 and R 1′ are the same and are hydrogen or a group —CH 2 R x wherein R x is either H or a C 1-3 alkyl group,
R 2 and R 2′ are the same and are hydrogen or a group —C(R y ) 3 wherein R y is either H or a C 1-3 alkyl group,
whereby either R 1 and R 1′ or R 2 and R 2′ are hydrogen,
R 3 and R 3′ are the same and are a linear C 1 to C 4 hydrocarbyl group,
R 4 and R 4′ are each a tert-butyl group, and
R 5 and R 5′ are each a linear C 1 to C 4 alkyl group.
6. The process according to claim 1 , wherein the complex of formula (I) is rac-Me 2 Si(2-Me-4-(3,5-Me 2 Ph)-5-OMe-6-tBu-Ind) 2 ZrCl 2 or rac-Me 2 Si(2-Me-4-(4-tBu-Ph)-5-OMe-6-tBu-Ind) 2 ZrCl 2 .
7. The process according to claim 1 , wherein the cocatalyst is an aluminoxane cocatalyst.
8. The process according to claim 7 , wherein in the formula (I) M is Zr and a ratio of Al/Zr is from 150 to 1000 mol/mol.
9. The process according to claim 1 , wherein the single site catalyst is in solid particulate form free from an external carrier.
10. The process according to claim 9 , wherein the single site catalyst is prepared by forming a liquid/liquid emulsion system, which comprises a solution of components (i) and (ii) dispersed in a solvent so as to form dispersed droplets, and solidifying said dispersed droplets to form solid particles.
11. The process according to claim 1 , wherein the heterophasic copolymer is prepared in a multistage process comprising at least two reactors connected in series including at least one gas phase polymerization step.
12. The process according to claim 1 , wherein the matrix (M) of the heterophasic polypropylene copolymer is a polypropylene homopolymer with a molecular weight distribution (MWD; M w /M n as measured with GPC) in a range of from 2.5 to 7.0.
13. The process according to claim 1 further comprising:
(A) polymerizing propylene and optionally ethylene in at least a first reactor and optionally a second reactor to form a polypropylene homopolymer or a propylene-ethylene random copolymer, said polypropylene homopolymer or propylene-ethylene random copolymer forming the matrix (M), and
(B) polymerizing propylene and ethylene in a gas phase reactor in the presence of the polypropylene homopolymer or propylene-ethylene random copolymer prepared in step (A) to form an elastomeric propylene-ethylene copolymer (E).
14. The process according to claim 13 , further comprising:
(a) polymerizing in a first reactor propylene and optionally ethylene to obtain a first polypropylene homopolymer or propylene-ethylene random copolymer fraction (R-PP1),
(b) transferring said first polypropylene homopolymer or propylene-ethylene random copolymer fraction (R-PP1) into a second reactor,
(c) polymerizing in said second reactor in the presence of the first polypropylene homopolymer or propylene-ethylene random copolymer fraction (R-PP1) propylene and optionally ethylene to obtain a second polypropylene homopolymer or propylene-ethylene random copolymer fraction (R-PP2), wherein said first polypropylene homopolymer or propylene-ethylene random copolymer fraction (R-PP1) and said second polypropylene homopolymer or propylene-ethylene random copolymer fraction (R-PP2) form the matrix (M),
(d) transferring said matrix (M) into a third reactor, wherein said third reactor is a gas phase reactor,
(e) polymerizing in said third reactor in the presence of the matrix (M) propylene, and
ethylene to obtain an elastomeric propylene-ethylene copolymer (E), wherein said matrix (M) and said elastomeric propylene-ethylene copolymer (E) form the heterophasic propylene copolymer.