New imidazolium bromide ionomers are prepared by halide displacement from brominated poly(isobutylene-co-isoprene) (BIIR) with a variety of imidazole-based nucleophiles. N-alkylation of butylimidazole (Bulm) by the allylic halide functionality within BIIR provides stable imidazolium bromide functionality in high yields. Characterization of the resulting thermoformable ionomer by dilute solution viscosity and solid-state rheology shows the effects of ion-pair aggregation on material properties over a range of ionomer composition. Knowledge of Bulm alkylations is extended to produce thermoset ionomer derivatives through solvent-free reactions of BIIR with 1,1'(1,4-butanediyl)bis(imidazole) and imidazole, whose physical properties stem from both a covalent network and a network of ion-pair aggregates. A novel method of preparing these thermosets is described, wherein a poly(isobutylene-co-isoprene) derivative bearing pendant imidazole functionality is prepared, and heated with BIIR parent material to yield covalent crosslinks comprised of dialkylated imidazole moieties. (C) 2011 Elsevier Ltd. All rights reserved.