This invention relates to organoaluminum compounds, organoaluminum activator systems, preferably supported, to polymerization catalyst systems containing these activator systems, and to polymerization processes utilizing the same. In particular, this invention relates to catalyst systems comprising ion-exchange layered silicate, a catalyst compound, an activator and an aluminum compound represented by formula: Al(R′)3−v(R″)v, wherein each R′, independently, is a C1-C30 hydrocarbyl group; each R″, independently, is a C4-C20 hydrocarbenyl group; and v is from 0.1 to 3.