Chain propagation constants in the cationic polymerization of styrene

Abstract

Perchloric acid initiates reproducible polymerization of styrene (unaffected by traces of water) in ethylene dichloride and mixtures with carbon tetrachloride over the temperature range 25–30°C. The rate of polymerization is accurately first order in monomer concentration, with a rate constant (k) proportional to the initial concentration of perchloric acid. The constant k/[HClO₄]₀ is identified with the rate constant for the propagation reaction (k_p), since in these polymerizations there is no true termination step, and the initiation rate is believed to be so fast as not to be rate‐determining. Values of the rate constants, activation energies, and frequency factors are presented. E_p and log k_p show linear relationships with the reciprocal of the dielectric constant (ε) of the solution in ethylene dichloride–carbon tetrachloride mixtures over the range ε = 5–10. In solution in ethyl chloride, and in ethylene dichloride mixtures with nitrobenzene and nitroethane, the rates are anomalously low.