Polymeric Ionic Liquid-Ligand Gels Exhibiting Transient Gel Behavior and Multivalent Ion Conductivity

The conduction of metal ions through solid polymeric electrolytes relies on favorable but highly dynamic interactions between mobile metal cations and polymer-bound solvating functionalities. Metal-ligand interactions have shown promise as solvating functionalities in solid polymer electrolytes due to their ability to strongly solvate metal salts while simultaneously conducting mono and multivalent metal ions in the solid state. These interactions simultaneously act as reversible cross-links, enhancing the storage modulus of the material over short timescales. Controlled poly(methyl acrylate)s with imidazole chain ends are synthesized as model polymers to investigate metal-ligand bond lifetimes and design rules for solid polymer electrolytes. Materials with a controlled number of imidazole ligands per chain are used to generate dynamic star-like and network topologies which relax to a disordered melt through metal-ligand bond dissociation. The network-forming materials are further used to probe the kinetics of cation-ligand association when the identity and valency of the metal cation is varied. Scaling arguments based on oscillatory rheology and electrical impedance measurements are used to support a hopping-type mechanism of ion conduction in metal-ligand coordinating polymers.