Impact of Methylaluminoxane Oxidation on Ethylene Polymerization Using Ni Catalysts

The effect of oxidation of methylaluminoxane (MAO) on ethylene polymerization was investigated to see the effect of aging and the possibility of using monomer gas that is not purified enough. In the polymerization using phenoxyimine-ligated titanium catalyst, almost no changes in polymerization behavior were observed until 35% of O2 was added to MAO at enough Al/Ti ratio. However, Brookhart-type nickel-diimine catalysts activated with oxidized MAO gave polyethylenes with improved molecular weight and linearity. NMR, UV–vis, and electron paramagnetic resonance studies combined with theoretical prediction revealed that the electronic property on nickel was consistent, regardless of MAO modification. The effect on the polymerization behavior can thus be explained by the change of steric effect of counteranions derived from MAO via modification with oxygen.