Norbornene polymerization was performed with monocyclopentadienyltitanium tribenzyloxide activated with methylaluminoxane (MAO). The catalyst afforded a pure vinyl-type polymer at temperatures below 80 degreesC and at appropriate MAO concentrations. However, at higher temperatures or high MAO concentrations, a portion of the titanium species was pyrolyzed to form an alkylidene compound that catalyzed the ring-opening metathesis polymerization of norbornene. As a result, both vinyl-type and ring-opening polymers were produced under the reaction conditions.