Absolute reactivity in the cationic polymerization of N-vinylcarbazole

Abstract

The cationic polymerization of N-vinylcarbazole initiated by tropylium hexachloroantimonate and tropylium perchlorate has been studied in detail. Initiation was rapid and complete and conversion to polymer was quantitative in all cases. Reaction rates were measured by an adiabatic calorimetric technique and half lives were of the order of 1–2 s. Catalyst concentrations employed were sufficiently low (< 10 −5 M for essentially complete dissociation into free ions, as indicated by the ion-pair dissociation constants. The rate coefficient for propagation by free cations in dichloromethane at 0°C is estimated as ∼3 × 10 +5 M −1 s −1, approximately five orders of magnitude greater than that for the corresponding free radical polymerization. Molecular weights were higher when SbCl 6 − was the counter-ion than with ClO 4 − and it is suggested that monomer transfer reactions occur more readily with the small equilibrium concentrations of ion pairs (allowing an effect of counter-ion), whereas propagation occurs predominantly via free cations. Initiation is shown to occur by addition of tropylium ion to the monomer double bond and detailed mechanisms for this, together with propagation and transfer reactions, are considered.