Alkyl-Substituted N-Vinylimidazolium Polymerized Ionic Liquids: Thermal Properties and Ionic Conductivities

Structure-property relationships for polymerized ionic liquids (PILs) relate chemical structure to ionic conductivity and reveal the importance of glass transition temperature (Tg) and the energy associated with an ion-hopping mechanism for ion conduction for a series of alkyl-substituted vinylimidazolium PILs. The alkyl-substituted vinylimidazolium-based PILs with varying lengths of n-alkyl substituents provide diverse precursors with exchangeable anions to further enhance thermal stability and ionic conductivity. As the anion size increases, regardless of alkyl substituent length, Tg decreases and the onset of weight loss, TD, increases. As the length of the alkyl substituent increases, Tg decreases for PILs with Br- and BF4- counteranions. Ionic conductivity increases over an order of magnitude upon exchange of the counteranion from TfO- < Tf2N-.