The invention related to a process for the polymerization of at least one aliphatic or aromatic hydrocarbyl C2-20 mono- or multiolefin in the presence of a catalyst and a boron comprising co-catalyst, wherein the catalyst comprises a composition of a metal-organic reagent, a spectator ligand and optionally at least one equivalent of a hydrocarbylating agent. The invention further relates to a polymer obtainable by the process of the invention.