Abstract: A ring-opening metathesis polymerisation (ROMP) reaction is disclosed in which a cyclic alkene compound is subjected to ROMP using a transition metal ROMP catalyst which has an alkyl moiety which is connected to the metal centre thereof through a double bond. The process includes the step of adding sufficient of an acyclic alkene having a carbon-carbon double bond capable of reacting with the catalytic metal moieties attached to the living end of each of the polymer chains generated in the ROMP reaction to end cap the polymer chains and to generate a stable olefin metathesis catalyst.