Ionomer derivatives of brominated poly(isobutylene-co-isoprene) rubber (BIIR) are prepared by alkylation of PPh₃,imidazole and 2-[2-(dimethylamino)ethoxy]ethanol under solvent-free conditions. Halide displacement is shown to be accompanied by allylic bromide rearrangement to kinetically more reactive endo-allylic bromide isomers. Alkylation to give quaternary onium-halide salts produces an isomerisation catalyst in situ, owing to a rapid S_N2′ isomerisation by free bromide. As a result, a continuous process for PPh₃ alkylation can be catalyzed by the recycling of a small amount of IIR-PPh₃Br product to the feed, thereby supporting an irreversible ionomer synthesis that proceeds to full conversion without the generation of reaction byproducts.