OLEFIN POLYMERIZATION USING SUPPORTED METALLOCENE CATALYSTS - DEVELOPMENT OF HIGH-ACTIVITY CATALYSTS FOR USE IN SLURRY AND GAS-PHASE ETHYLENE POLYMERIZATIONS

Reaction of hydroxylated silica and alumina supports with methyl alumi noxane in toluene suspension provides chemically modified supports sui table for use in slurry and gas-phase polymerizations of ethylene or p ropylene on treatment with a variety of metallocene dichloride complex es. In particular, aluminas derived from calcination of sol-gel precur sors feature high degrees of surface hydroxylation in comparison with commercially available silica (or even alumina) of similar surface are a and total porosity. This feature provides a mechanism for increasing the amount of aluminoxane on the former supports, such that commercia lly acceptable productivities (> 10 kg PE/g support x h) are observed at relatively low, total levels of aluminoxane or other alkylaluminum compounds in slurry or gas-phase polymerizations, respectively. A vari ety of evidence indicates that leaching of active catalyst from these alumina supports occurs to a minor extent under slurry conditions, par ticularly at higher temperatures in the presence of additional alumino xane. At lower temperatures, this does not occur to an appreciable ext ent but the morphology and bulk density of the polymer formed is unsui table for use in a gas-phase process. This can be attributed to the me thod for synthesis of the sol-gel alumina precursor which results in i rregular particles with a broad particle size distribution. Copolymeri zation of ethylene with 1-octene or I-hexene results in formation of l inear, low density, PE with a narrow composition distribution as revea led by temperature rising elution fractionation. These studies indicat e that less comonomer is incorporated using these supported metallocen e catalysts than their soluble analogues under otherwise identical con ditions. Finally, some of the resins prepared under slurry conditions land to a lesser extent in a gas-phase process), exhibit properties co nsistent with the presence of low levels of long-chain branching; this feature appears to be reasonably general for a variety of simple meta llocene complexes. (C) 1998 Elsevier Science B.V.