Catalyst composition with mixed selectivity control agent and method
View Patent ↗The present disclosure provides a Ziegler-Natta catalyst composition comprising a procatalyst, a cocatalyst and a mixed external electron donor comprising a first selectivity control agent, a second selectivity control agent, and an activity limiting agent. A polymerization process incorporating the present catalyst composition produces a high-stiffness propylene-based polymer with a melt flow rate greater than about 50 g/10 min. The polymerization process occurs in a single reactor, utilizing standard hydrogen concentration with no visbreaking.
1. A catalyst composition comprising:
a Ziegler-Natta procatalyst composition comprising titanium, magnesium and an internal electron donor;
a cocatalyst; and
a mixed external electron donor (M-EED) comprising an activity limiting agent (ALA), a first selectivity control agent (SCA1) comprising an alkoxysilane, a second selectivity control agent (SCA2) selected from the group consisting of an alkoxysilane, a diether, and a dialkoxybenzene, a SCA1:SCA2 mole ratio from 0.1-1.0:1, a mole ratio of total-SCA to ALA less than 1.0, and the catalyst composition is a self-limiting catalyst composition.
2. The catalyst composition of claim 1 wherein the procatalyst composition comprises an internal electron donor comprising a bidentate composition.
3. The catalyst composition of claim 1 wherein the SCA1 comprises a member selected from the group consisting of a dimethoxysilane, a dimethoxysilane having at least one secondary alkyl group, a dimethoxysilane having a secondary amino group directly bonded to the silicon atom, and combinations thereof.
4. The catalyst composition of claim 1 wherein SCA2 is selected from the group consisting of a diethoxysilane, a triethoxysilane, a tetraethoxysilane, a trimethoxysilane, a diether, a dialkoxybenzene, a dimethoxysilane containing two linear alkyl groups, a dimethoxysilane containing two alkenyl groups, and combinations thereof.
5. The catalyst composition of claim 1 wherein the ALA is selected from the group consisting of an aromatic ester or a derivative thereof, an aliphatic ester or a derivative thereof, a diether, a poly(alkylene glycol) ester, and combinations thereof.
6. The catalyst composition of claim 1 comprising an aluminum-containing cocatalyst and a mole ratio of A1to M-EED less than about 6.0.
7. The catalyst composition of claim 1 wherein SCA1 comprises dicyclopentyldimethoxysilane.
8. The catalyst composition of claim 1 wherein SCA2 is selected from the group consisting of methylcyclohexyldiethoxysilane, di-isobutyldiethoxysilane, n-propyltriethoxysilane, tetraethoxysilane, di-n-butyl-dimethoxysilane, benzyltriethoxysilane, but-3-enyltriethoxysilane, 1-(triethoxysilyl)-2-pentene, (triethoxysilyl)cyclohexane, and combinations thereof.
9. The catalyst composition of claim 1 wherein the ALA comprises isopropyl myristate.
10. The catalyst composition of claim 1 wherein SCA1 comprises dicyclopentyldimethoxysilane and SCA2 is selected from the group consisting of methylcyclohexyldimethoxysilane, di-n-butyl-dimethoxysilane, n-propyltriethoxysilane, benzyltriethoxysilane, and (triethoxysilyl)cyclohexane.
11. The catalyst composition of claim 1 wherein SCA1 comprises dicyclopentyldimethoxysilane and SCA2 comprises 1-ethoxy-2-n -pentoxybenzene.
12. The catalyst composition of claim 1 wherein the ALA comprises a C 1-4 alkyl ester of aliphatic C 8-20 monocarboxylic acid.
13. The catalyst composition of claim 1 wherein the procatalyst composition comprises a phthalate.
14. The catalyst composition of claim 1 wherein SCA1 is selected from the group consisting of dicyclopentyldimethoxysilane and diisopropyldimethoxysilane and SCA2 is selected from the group consisting of vinyltriethoxysilane, dimethyldimethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, and tetraethoxysilane.
15. The catalyst composition of claim 1 wherein the M-EED comprises from 5 mol % to 10 mol % total SCA and from 95 mol % to 90 mol % ALA.