Morphology, mechanical properties, and intermolecular interactions of ion gels based on phosphonic acid polymers

Ion gels prepared by immobilizing ionic liquids in polymer matrices have advantages of fast ion diffusion and easy control of mechanical properties over conventional solid electrolytes. Particularly, facile processability and reversibility of ion gels based on physical crosslinking networks have attracted recent attention. In the present study, we investigated phosphonic acid-based ion gels, where the intermolecular interactions were chemically controlled. Two approaches were used for the preparation of ion gels: (1) controlled polymerization of phosphonate styrene monomers in which the bonding position of the phosphonic acid group was precisely controlled and (2) introduction of various ionic liquids having dissimilar anions. This allowed the effective modulation of ionic interactions between the phosphonic acid groups and the ionic liquids, yielding significantly different chain packing structures, mechanical properties, and ion transport properties of the resultant ion gels. Investigation on ion gels based on phosphonic acid block copolymers was also conducted by focusing on the effect of types of ionophobic blocks and local concentration of phosphonic acid groups on the characteristics of ion gels.