Reactivity and mechanism in the cationic polymerization of isobutyl vinyl ether

The cationic polymerization of isobutyl vinyl ether initiated by triphenyl methyl and tropylium hexachloroantimonates, and by triphenyl methyl tetrafluoroborate, has been studied in detail. Initiation was rapid and complete, termination was shown to be insignificant, polymerization half lives were of the order of 5–10 s and reaction rates were measured by an adiabatic calorimetric technique. Catalyst concentrations employed were sufficiently low that essentially complete dissociation into free ions is indicated by ion-pair dissociation constants, and this permits estimation of the rate coefficient for propagation by free cations (k_p). At 0°C in methylene dichloride k_p ∼ 5 × 10³ M⁻¹ s⁻¹, in substantial agreement with values obtained by radiation induced polymeirzation of bulk monomer. Molecular weights of the poly(isobutyl vinyl ether) samples fell in the range 2000–5000 on account of monomer transfer processes. Detailed mechanisms for initiation, propagation, transfer and termination reactions are considered.