Homogeneous Polymer Network Ion Gels Based on Metal Ion-Complexation-Induced Cross-Linking in Ionic Liquids

We report a facile one-step synthesis of homogeneous polymer network ion gels. The end-functionalization of tetra-branched poly(ethylene glycol) (TetraPEG) with catecholamine (Cat–NH2) and the complexation between metal ions and Cat groups proceeded simultaneously in ionic liquid to yield free-standing TetraPEG ion gels cross-linked by the metal–Cat complexes. The mechanical strength of the ion gels strongly depended on the coordination bond strengths of the metal–Cat complexes, displaying the following trend: Ni2+ > Mg2+ > Li+. We measured their ionic conductivities and found that the ion gels exhibited high ionic conductivity regardless of the employed metal ions.