Imidazolium cations form molten salts and exhibit excellent ionic conductivity because of their very low melting points or low glass transition temperature. This phenomenon depends strongly on the characteristics of the anion species. Some derivatives having vinyl groups are obtained as highly ion-conductive molten salt, but conductivity drops greatly after polymerization. To minimize this drop in conductivity the vinyl group and molten salt unit were tethered with oligo(ethylene oxide). The ionic conductivity of the polymers improved by a factor of 100. Further improvement took place when a hydrocarbon chain was used instead of oligo(ethylene oxide). Molecular design of the molten salt polymers for higher ionic conductivity is discussed.