The process of claim 10, wherein the metallocene compound is represented by the formula: (C5 Rx)y R'z (C5 Rm)MQn-y-1(I) wherein: M is a metal of Groups III to VIII of the Periodic Table of the Elements; (C5 Rx) and (C5 Rm) are the same or different cyclopentadienyl or substituted cyclopentadienyl groups bonded to M; R is the same or different and is hydrogen or a hydrocarbyl radical such as alkyl,