The described invention provides a low fouling, high particle density polymerization process and an olefin polymerization catalyst composition comprising the reaction product of a) an organic polymeric support i) having a surface area of from about 1 to 10 m.sup.2 /g and ii) functionalized with an acidic proton-containing ammonium salt of a non-coordinating anion, and b) an organometallic transition metal compound having ancillary ligands, at least one labile ligand capable of abstraction by protonation by said ammonium salt and at least one labile ligand into which an olefinic monomer can insert for polymerization. In a preferred embodiment, the polymeric support has a surface area of .ltoreq.10 m.sup.2 /g and is particularly suitable for use with high activity organometallic, transition metal catalyst compounds.