This invention is directed to a process for the preparation of polyolefins from one or more olefinic monomers comprising combining said olefins under olefin polymerization conditions with an organometallic catalyst compound that is activated for olefin polymerization by reaction with at least one Lewis acid aluminum compound of the formula RnAl(ArHal)3-n, where 'ArHal' is a halogenated aryl group, n=1 or 2, and R is a monoanionic group other than a halogenated aryl group. The invention also relates to a polymer produced using the process and to the polymer itself.