Novel polymer electrolytes prepared by copolymerization of ionic liquid monomers

Ionic liquid monomer couples were prepared by the neutralization of 1‐vinylimidazole with vinylsulfonic acid or 3‐sulfopropyl acrylate. These ionic liquid monomer couples were viscous liquid at room temperature and showed low glass transition temperature (Tg) at −83 °C and −73 °C, respectively. These monomer couples were copolymerized to prepare ion conductive polymer matrix. Thus prepared ionic liquid copolymers had no carrier ions, and they showed very low ionic conductivity of below 10⁻⁹ S cm⁻¹. Equimolar amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to imidazolium salt unit was then added to generate carrier ions in the ionic liquid copolymers. Poly(vinylimidazolium‐co‐vinylsulfonate) containing equimolar LiTFSI showed the ionic conductivity of 4 × 10⁻⁸ S cm⁻¹ at 30 °C. Advanced copolymer, poly(vinylimidazolium‐co‐3‐sulfopropyl acrylate) which has flexible spacer between the anionic charge and polymer main chain, showed the ionic conductivity of about 10⁻⁶ S cm⁻¹ at 30 °C, which is 100 times higher than that of copolymer without spacer. Even an excess amount of LiTFSI was added, the ionic conductivity of the copolymer kept this conductivity. This tendency is completely different from the typical polyether systems. Copyright © 2002 John Wiley & Sons, Ltd.