Revisiting living and apparently living carbocationic polymerizations

Abstract

This short review aims at reconsidering the behaviours of a few vinyl monomers (isobutylvinylether, p-methylstyrene, p-methoxystyrene, indene and 2,4,6-trimethylstyrene) well identified as leading to different levels of living character during their cationic polymerization. These polymerizations agree well with the general scheme of dormant-active equilibrium of propagating species. The available data, and particularly that from of our Paris group, are summed up and discussed in terms of cation stability and of absence (or non-detection) of transfer depending on the conditions of polymerization (nature of the monomer, initiating system, temperature, medium, range of considered M n , etc.). This living situation allows the estimation of the absolute k p ± (propagation rate constant) for the considered monomers, either via the determination of the concentration of active ionic species (ISC -ionic species concentration method) or via the capping method (diffusion clock or DC method). A discrepancy still persists between the two approaches as the DC method leads to k p ± which are 10 5 times larger. Furthermore the capping rate constants k c ± and the corresponding k p ± obtained through the DC method have led to the conclusion that the effect of a monomer substituent on the reactivity of carbocation is much larger than the effect on the reactivity of the corresponding monomer. But, from the k p ± values obtained by the ISC method and from the reactivity ratios in copolymerization of the styrenic monomers, we concluded that there could be an approximate compensation between carbocation and monomer reactivities.