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.