New isobutylene-rich elastomers bearing multiple pendant styrenic, acrylic, maleimidic, vinylic, and allylic functional groups have been prepared and examined in the context of peroxide-initiated crosslinking. Halide displacement from brominated poly(isobutylene-co-isoprene) (BIIR) by the requisite carboxylate nucleophiles in homogeneous toluene solutions provide the desired esters in quantitative yield without complications from dehydrohalogenation or premature crosslinking. Heating the resulting macromonomers with dicumyl peroxide to 160 C under solvent-free conditions gives thermoset derivatives, with reaction rates and yields depending markedly on functional group structure. In general, high cure extents can only be achieved using highly reactive pendant functional groups, owing to the competitive balance between crosslinking through C@C oligomerization, and degradation through b-scission of backbone macroradical intermediates. Independent control of crosslinking rates and cure extents is gained through the use of nitroxyl radical traps bearing acrylate functionality.

The yield and regioselectivity of H-atom abstraction by cumyloxy radicals from poly(isobutylene-co-isoprene) (IIR) are quantified and discussed in the context of cross-linking/ degradation outcomes and vinyltriethoxysilane (VTEOS) graft yields. Studies of IIR materials with different isoprene contents show that H-atom abstraction from the allylic functionality provided by isoprene mers is responsible for the heightened Hatom transfer reactivity of IIR relative to poly(isobutylene). Differences in the reactivity of allylic and alkyl macroradical intermediates makes high isoprene IIR materials less prone to peroxide-initiated chain scission, but less responsive to VTEOS grafting formulations. Improved knowledge of H-atom transfer reactivity is extended to a new approach for IIR cross-linking involving acrylate-functionalized nitroxyl chemistry.

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