Method for making polyolefins
View Patent ↗A method for making ethylene polymers and copolymers is disclosed. The method uses a catalyst system comprising a low level of an aluminum-containing activator, a bridged indenoindolyl transition metal complex, and a treated silica support. The method enables economical preparation of ethylene copolymers having very low density. The silica-supported, bridged complexes incorporate comonomers efficiently and are valuable for a commercial slurry loop process. Use of a bridged indeno[2,1-b]indolyl complex provides exceptionally efficient comonomer incorporation, and gives polymers with a substantial and controlled level of long-chain branching. The method facilitates the production of a wide variety of polyolefins, from HDPE to plastomers.
1. A method which comprises copolymerizing ethylene and a 1-olefin in the presence of a catalyst system comprising (a) an aluminum-containing activator; (b) a bridged, indenoindolyl Group 3-10 transition metal complex; and (c) an alumoxane-treated silica support, to produce a linear low density or plastomeric ethylene copolymer having a density less than 0.930 g/cm 3 , wherein the catalyst system has an aluminum:transition metal [Al:M] mole ratio less than 500.
2. The method of claim 1 wherein the complex includes a Group 4-6 transition metal.
3. The method of claim 1 wherein the complex includes an indeno[2,1-b]indolyl ligand.
4. The method of claim 1 wherein the complex includes an indeno[1 2-b]indolyl ligand.
5. The method of claim 1 wherein the complex incorporates a bridging group selected from the group consisting of methylene, dimethylene, isopropylidene, and dimethylsilyl.
6. The method of claim 1 wherein an indenoindolyl ligand of the complex is covalently bridged to a polymerization-stable ligand selected from the group consisting of cyclopentadienyl, indenyl, and fluorenyl.
7. The method of claim 1 wherein the activator is methylalumoxane or a mixture of methylalumoxane and an organoborane.
8. The method of claim 7 wherein the organoborane is tris-(pentafluorophenyl)borane.
9. The method of claim 1 wherein the [Al:M] mole ratio is less than about 250.
10. The method of claim 1 wherein the 1-olefin is selected from the group consisting of propylene, 1-butene, 1-hexene, 1-octene, and mixtures thereof.
11. The method of claim 1 wherein the ethylene copolymer has a density less than 0.920 g/cm 3 .
12. The method of claim 1 wherein the ethylene copolymer has a density less than 0.910 g/cm 3 .
13. The method of claim 1 wherein the ethylene copolymer has a density less than 0.900 g/cm 3 .
14. The method of claim 1 wherein the ethylene copolymer has a Mw/Mn<4.0.
15. The method of claim 1 performed in the presence of a chain-transfer agent selected from the group consisting of hydrogen, organozinc compounds, and organoaluminum compounds, to produce a copolymer having Mw<150,000.
16. The method of claim 15 wherein the chain-transfer agent is triethylaluminum in combination with hydrogen, and the copolymer has a Mw/Mn<3.5.
17. The method of claim 1 performed in the absence of a chain-transfer agent to produce a copolymer having Mw>400,000.
18. The method of claim 1 wherein the complex incorporates a fluorenyl ligand, and the resulting copolymer has a Mw>200,000.
19. A method which comprises polymerizing ethylene and optionally a 1-olefin in the presence of a catalyst system comprising (a) an aluminum-containing activator; (b) a bridged, indeno[2,1-b]indolyl Group 3-10 transition metal complex; and (c) an alumoxane-treated silica support, to produce an ethylene polymer or copolymer having a long-chain-branching index>0.2, wherein the catalyst system has an aluminum:transition metal [Al:M] mole ratio less than 500.
20. The method of claim 19 wherein the complex incorporates a bridging group selected from the group consisting of methylene, dimethylene, isopropylidene, and dimethylsilyl.
21. The method of claim 19 wherein an indeno[2,1-b]indolyl ligand of the complex is covalently bridged to a polymerization-stable ligand selected from the group consisting of cyclopentadienyl, indenyl, and fluorenyl.
22. The method of claim 19 wherein the [Al:M] mole ratio is less than about 250.
23. The method of claim 19 wherein the polymer or copolymer has a long-chain-branching index>0.5.
24. The method of claim 19 wherein the polymer or copolymer has a long-chain-branching index>1.0.
25. The method of claim 19 wherein the polymer or copolymer has a Mw/Mn<4.0.
26. The method of claim 19 wherein the 1-olefin is selected from the group consisting of propylene, 1-butene, 1-hexene, 1-octene, and mixtures thereof.
27. The method of claim 26 wherein the copolymer is plastomeric and has a density less than 0.915 g/cm 3 .
28. The method of claim 27 wherein the copolymer has a density less than 0.900 g/cm 3 .
29. The method of claim 19 wherein the transition metal complex incorporates a dimethylsilyl bridging group, the 1-olefin is 1-hexene, the mole ratio of 1-hexene to ethylene is at least about 0.3, and the resulting copolymer has a long-chain-branching index>1.0.