This invention relates to a process to prepare a trialkylaluminum treated support comprising: 1) combining a support with first trialkylaluminum compound(s), where the alkyl groups have at least 2 carbon atoms; then 2) calcining the combination of the support and the trialkylaluminum compound(s); then 3) combining the calcined support with second trialkylaluminum compound(s), where the alkyl groups have at least 2 carbon atoms; where the first and second trialkylaluminum compound(s) may be the same or different. This invention further relates to catalyst systems comprising catalyst compounds and such supports, as well as processes to polymerize unsaturated monomers using the supports in combination with catalyst compounds.