Supported catalysts which reduce sheeting in olefin polymerization, process for the preparation and the use thereof
Olefin polymerization in the presence of heterogeneous supported catalysts is improved by incorporating into the supported catalyst a unifunctional hydrophobic tether comprising a hydrophobic portion containing no basic nitrogen and a univalent reactive group. The unifunctional hydrophobic tether reduces fouling and sheeting in gas phase polymerization processes and improves polymer morphology and bulk density in slurry polymerization processes, while substantially maintaining or enhancing catalyst polymerization activity.
1. In an olefin polymerization catalyst suitable for the polymerization of one or more olefin monomers in which a heterogeneous catalyst comprising an organometallic precatalyst is employed with an activator on a particulate, porous inorganic support, the improvement comprising:
depositing onto said heterogeneous catalyst, a unifunctional hydrophobic tether comprising a hydrophobic portion and a unifunctional reactive group, said unifunctional hydrophobic tether being free of basic nitrogen, and tethered to said heterogenous catalyst at but a single site on said heterogenous catalyst.
2. The catalyst of claim 1 wherein the hydrophobic portion of said unifunctional hydrophobic tether comprises a C 6-24 branched or unbranched, optionally fluorinated aliphatic hydrocarbon group, a highly fluorinated aliphatic hydrocarbon containing minimally 4 carbon atoms; an organopolysiloxane containing at least 5 silicon atoms, or a compound containing both Si—C bonded aliphatic hydrocarbon moieties and diorganosiloxy moieties wherein the sum of half the number of carbon atoms in the aliphatic hydrocarbon moieties plus the number of silicon atoms in the diorganosiloxy groups is minimally 4.
3. The catalyst of claim 1 , wherein said unifunctional reactive group is selected from the group consisting of hydroxyl, epoxy, quaternary ammoniumm, thiol, aldehyde, hydrolyzable silane, Si—H functional silane, aluminate, and borate.
4. The catalyst of claim 1 , wherein said hydrophobic portion comprises a C 10-24 optionally branched aliphatic hydrocarbon, a perfluorinated C 6-10 aliphatic hydrocarbon, or an Si 5-10 diorganopolysiloxane.
5. The catalyst of claim 1 , wherein said unifunctional hydrophobic tether is selected from the group consisting of fatty alkanols, C 8-24 -substituted silanes, and fatty quaternary ammonium halides.
6. The catalyst of claim 1 , wherein said unifunctional hydrophobic tether is applied to said porous inorganic support dissolved in a volume of solvent which is less than 1.5 times the pore volume of the porous inorganic support.
7. The catalyst of claim 1 , wherein said unifunctional hydrophobic tether is applied to said porous inorganic support in admixture with an alumoxane in organic solvent.
8. The catalyst of claim 1 , wherein a first portion of unifunctional hydrophobic tether is added to said porous inorganic support in admixture with a first portion of an alumoxane in solvent in a total amount of liquid which is less than twice the pore volume of said porous inorganic support, solvent is optionally removed, and a second portion of said unifunctional hydrophobic tether, a second portion of an alumoxane, and at least a portion of said single site precatalyst in solvent are added, the amounts of liquid phase being such that a slurry is not formed.
9. The catalyst of claim 1 , wherein said activator consists essentially of an alumoxane.
10. The catalyst of claim 1 , wherein said activator comprises a bulky anionic ligand.