Activation of the pre-activated catalyst precursor, prior to polymerization, can be accomplished by feeding a slurry of the pre-activated precursor into a suitable reactor under a nitrogen atmosphere, typically in an inert hydrocarbon diluent, such as hexane, heptane, isopentane, toluene, mineral oil or other hydrocarbons known to be useful in the field, followed by the addition of an alumoxane-ba