Titanium/MAO-based catalyst systems were used to synthesise polycyclic olefins containing both vinyl and ring-opened units by converting the mechanism of polymerisation from vinyl addition (VA) to metathesis. The switch in mechanism was achieved by adding a reactivity transfer reagent like phenylacetylene (PA) during the course of VA polymerisation. The polymers synthesised contained nearly 30% ring-opened structures as indicated by their H-1 nuclear magnetic resonance (NMR). Kinetic studies indicated a change in mechanism of polymerisation after the addition of the reactivity transfer reagent. Arrhenius parameters calculated for both VA and metathesis polymerisation also suggested mechanism switching in the course of polymerisation.