Studies in switching the mechanism of polymerisation by single-site catalysts - from vinyl addition to metathesis

Titanium/MAO-based catalyst systems were used to synthesise polycyclic olef ins containing both vinyl and ring-opened units by converting the mechanism of polymerisation from vinyl addition (VA) to metathesis. The switch in me chanism was achieved by adding a reactivity transfer reagent like phenylace tylene (PA) during the course of VA polymerisation. The polymers synthesise d contained nearly 30% ring-opened structures as indicated by their H-1 nuc lear magnetic resonance (NMR). Kinetic studies indicated a change in mechan ism 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. (C) 20 00 Elsevier Science B.V. All rights reserved.