The propagation rate-constants of the cationic polymerization of some alkenes in nitrobenzene—IV. Not the real kp+

Abstract

The cationic polymerization of several alkenes, including vinyl ethers (VE), by carbenium and carboxonium salts in nitrobenzene had given propagation rate-constants which were interpreted by us as being the k p + as defined by the equation − dm dt = k p + · [P n +] · m, where [P n +] is the concentration of unpaired, uncomplexed propagating cations. The purpose of the present paper is to show that our own work contains evidence, not understood and neglected at the time, indicating that this is not correct. An interpretation has been devised which is compatible with all the facts, including the very low values of the rate-constants (now called k p +A), the bimodal DPD of the poly(2-chloroethylvinyl ethers), and the antibatic correlation between the k p +A and the enthalpy of polymerization for three hydrocarbons and two VE. This is based on the idea, introduced by others, that the propagating carbenium ions cationate the solvent, Sv, giving the ions P nSv +, i.e. P nON +(O)C 6H 5, which are in equilibrium with the P n +. The observed k p +A are weighted means of the propagation rate-constants of the two propagating species. A propagation mechanism for the P nSv + has been suggested which resembles closely that for pseudocationic polymerizations [8].