Imidazolium Bromide Derivatives of Brominated Poly(isobutylene-co-para-methylstyrene): Synthesis of Peroxide-Curable Ionomeric Elastomers

A series of new elastomeric ionomers is prepared through halide displacement from brominated poly­(isobutylene-co-para-methylstyrene) (BIMS) by a range of N-substituted imidazoles. Studies of the dynamics of solvent-borne and solvent-free reactions demonstrate the influence of N-substituent structure on nucleophilicity, with alkyl and allyl groups providing greater reactivity than vinyl functionality. Ionomers bearing pendant styrenic, methacrylic, vinylic, and allylic functionality are cross-linked by standard peroxide initiators to give thermoset derivatives, with reaction rates and yields depending markedly on functional group structure. The discovery of a benzylic N-allylimidazolium ionomer is particularly important, as this material is amenable to solvent-free preparations, and provides a unique combination of moderate cross-linking rates and high cure extents, owing to a balance of radical addition and H-atom transfer reactivity. Physical properties of the resulting thermosets are a product of their hybrid ionic/covalent network, as the material response to deformation is affected by a stable covalent network as well as a labile network of aggregated ion pairs.