Effect of minor additives of arenes on chain termination in low-temperature cationic polymerization of isobutylene in aliphatic solvents

Abstract

The influence of small concentrations (1—8 mmol L^–1) of arenes (viz., hexafluorobenzene, chlorobenzene, benzene, toluene, and mesitylene) on the molecular weight, molecular weight distribution, and degree of functionalization by terminal olefin groups was studied for polymers prepared by low-temperature (–78 °C) isobutylene polymerization in n-hexane initiated by the MeOH—AlBr₃ and Bu^tCl—AlBr₃ systems. The criteria “extent of livingness” k _el/k _p were calculated, where k _el and k _p are the rate constants of proton elimination and chain propagation, respectively. It was established that arenes can be involved in proton elimination from the growing carbocation, and their activity in this process increases with an increase in the basicity. Arenonium ions formed by the interaction of arenes with the components of the initiating system or with the growing ionic active centers can form complexes with counteranions, thus retarding proton elimination with the transfer to the counterion.