Covalent Incorporation of Ionic Liquid into Ion-Conductive Networks via Thiol–Ene Photopolymerization

Abstract

Ene-functionalized ionic liquids with a range of different cationic groups and counteranions react stoichiometrically within a tetrathiol-divinyl ether formulation within 20 minutes to form thiol–ene polymers with measurable ionic conductivities via a photoinitiated polymerization and crosslinking reaction. Dynamic mechanical analysis indicates that these networks are more spatially heterogeneous and possess higher glass transition temperatures (Tg) compared with thiol–ene formulations without charge. While tuning the molar content of ionic liquid monomer is one method for adjusting the crosslink and charge densities of the thiol–ene polymeric ionic liquid networks, the presence of cation–anion interactions also plays a critical role in dictating the thermomechanical and conductive properties. Particularly, while cationic structure effects are not significant on the polymer properties, the use of a weakly coordinating hydrophobic anion (bistriflimide) instead of bromide-based networks results in an apparent decrease in hydrated ion conductivity (7.4 to 1.5 mS cm−1) and Tg (−9.6 to −17.8 °C). (Figure presented.).