Pendent Sulfonylimide Ionic Liquid Monomers and Ionoelastomers via SuFEx Click Chemistry
Owen A. Lee, Matthew K. McBride, Matthew Ticknor, Joshua Sharpes, Ryan C. Hayward
Abstract
Anionic polymerized ionic liquids with a fixed sulfonylimide group have emerged as promising materials for energy storage applications, electromechanical devices, and gas separation membranes due to their highly delocalized anionic charges. However, synthetic challenges have limited the production of high-purity poly(sulfonylimide)s at scale and hindered systematic evaluation of their properties. We report a synthetic route for the production of high-purity sulfonylimide monomers at >10 g scales using a sulfur(VI) fluoride exchange (SuFEx) click reaction. Pendent sulfonylimide acrylate monomers with 1-ethyl-3-methylimidazolium counterions were synthesized with perfluorinated side groups of different lengths and cross-linked to form ionoelastomers. The networks were stretchable (≈120% strain at break), showed high solvent-free ionic conductivity (>3.8 × 10 –3 mS/cm), and were hydrophobic with water contact angles >105°. The imidazolium counterions interact strongly with the perfluorinated side chains, yielding nonmonotonic trends in ionic conductivity and modulus relative to the glass transition temperature ( T g ). Wide-angle X-ray scattering and vibrational spectroscopies reveal that shorter perfluorinated side groups promote cation dissociation, while longer chains cause ionic aggregation. We expect that this SuFEx approach will expand access to next-generation poly(sulfonylimide) electrolytes for a variety of applications and here demonstrate its utility for providing new insight into the molecular-level design of poly(sulfonylimide) ionoelastomers.