Ethylene polymerization with silica-supported nickel-diimine catalyst: Effect of support and polymerization conditions on catalyst activity and polymer properties

Ethylene was polymerized using both homogeneous and modified methylaluminoxane (MMAO)-treated silica supported nickel-diimine catalysts (1,4-bis(2,6-diisopropylphenyl) acenaphthene diimine nickel(II) dibromide) in a slurry semibatch reactor. The effects of catalyst support and polymerization conditions (ethylene pressure and reaction temperature) on catalyst activity and polymer properties were systematically investigated. The supported catalyst gave far lower activity than the homogeneous catalyst. The activities of both catalyst systems increased with polymerization temperature with a maximum at 40degreesC. Compared with the homogeneous catalyst, the supported catalyst system produced polyethylene with a different microstructure. Due to steric effects, the supported catalyst system exhibited lower chain walking rates than the homogeneous catalyst, producing polymers with less branching content and, thus higher melting points. Depending on polymerization conditions, two active site populations were observed during polymerization supported catalyst; one population remained fixed on the surface of the support, and the other was extracted from the support, exhibiting the same polymerization behavior as the homogeneous catalyst. [GRAPHICS] DSC thermograms for polyethylene produced with homogeneous and supported catalysts at an ethylene pressure of 50 psig (3.45 (.) 10(5) Pa) and reaction temperature 40degreesC.