Processes of forming a supported activated catalyst composition and method of polymerization are disclosed, the process of forming the composition including combining a halogenated aromatic aluminum activator compound with a fluorinated support and a catalyst to form a supported activated catalyst composition. Also disclosed is a supported activated catalyst composition, comprising the reaction product of a fluorinated support, a perfluorophenyl aluminum activator and in one embodiment a metallocene catalyst. In one embodiment, the halogenated aromatic aluminum activator is represented by the formula R.sub.nAl(ArHal).sub.3-n, wherein ArHal is a halogenated aryl group, R is a monoanionic ligand, and n is 1 or 2.