The invention is directed to polyalphaolefins (PAOs) and processes for forming PAOs. In one embodiment, the invention is to a process for forming a PAO comprising polymerizing C8-C12 α-olefin monomers in the presence of hydrogen, a C8-C12 saturated hydrocarbon, e.g., a C8-C12 saturated straight-chain hydrocarbon, and a catalyst system in a reaction vessel, wherein the C8-C12 saturated straight-chain hydrocarbon has about the same number of carbon atoms as the C8-C12 α-olefin monomers. The C8-C12 saturated straight-chain hydrocarbon optionally is derived from a crude PAO product formed by the process of the invention. The invention is also directed to reaction systems for performing the processes of the invention, to processes for controlling PAO viscosity based on residence time, and to the removal of spent catalyst using a solid adsorbent particles.