The preparation of isobutylene-based ionomers through displacement of halide from brominated poly(isobutylene-co-isoprene) (BIIR) by triphenylphosphine (PPh3) and N,N-dimethyloctylamine (DMOA) is demonstrated. While the resulting phosphonium and ammonium bromide salts (IIR-PPh3Br and IIR-NR3Br, respectively) possess dynamic mechanical properties that are comparable to thermoset vulcanizates, the elastomeric network is the result of ion-pair aggregation. Evidence of intra-and intermolecular aggregation provided by dynamic mechanical and dilute solution viscosity analyses is reinforced by studies of H-1 NMR spin-spin relaxation, which demonstrate the reduced mobility of those polymer chain segments proximal to the phosphonium bromide functionality within IIR-PPh3Br.