Abstract: A liquid phase polymerization process is provided for producing a polyolefin elastomer, e.g., one derived from ethylene, another &agr;-olefin such as propylene and optionally, a diene, employing a metallocene catalyst. The process comprises contacting monomer under liquid phase polymerization conditions with a catalyst composition obtained by combining (a) a metallocene procatalyst, preferably one containing a bridging group possessing at least two bulky groups, and (b) a cocatalyst such as aluminoxane, preferably a cation-generating cocatalyst, in partial or total replacement of aluminoxane.