Decoupling Bulk Mechanics and Mono- and Multivalent Ion Transport in Polymers Based on Metal–Ligand Coordination

Abstract

Decoupling bulk mechanics and ion conduction in conventional ion conducting polymers is challenging due to their mutual dependence on segmental chain dynamics. Polymers based on dynamic metal–ligand coordination are promising materials toward this aim. This work examines the effect of the nature and concentration of metal bis(trifluoromethylsulfonyl)imide (MTFSI) salts on the mechanical properties and ionic conductivity of poly[(ethylene oxide)-stat-(allyl glycidyl ether)] functionalized with tethered imidazole ligands (PIGE). Varying the cation identity of metal salts mixed in PIGE enables dramatic tunability of the zero-frequency viscosity from 0.3 to 100 kPa s. The ionic conductivity remains comparable at approximately 16 μS cm–1 among mono-, di-, and trivalent salts at constant metal-to-ligand molar ratios due to negligible changes in glass transition temperatures at low ion concentrations. Thus, polymers based on metal–ligand coordination enable decoupling of polymer zero-frequency viscosity from ion conduction. Pulsed-field-gradient NMR on PIGE containing Li+ or Zn2+ salts complement electrochemical impedance spectroscopy to demonstrate that both the anion and cation contribute to ionic conductivity.