Proton diffusion in polyelectrolytes based on hydrogenated polynorbornenes with imide side groups in the repeat unit as determined by NMR and impedance spectroscopies

The conductivity of sulfonated membranes based on hydrogenated polynorbornene functionalized with dicarboximide side groups, specifically hydrogenated poly(exo,endo-N-phenyl-norbornene-5,6-dicarboximide), was determined by impedance spectroscopy in the temperature range 10–40 °C. Using Nernst–Planck transport equations, the diffusion coefficient of protons in the membranes was estimated. The diffusion of protons was also measured by pulsed field gradient (PFG) NMR techniques at several temperatures. The comparison of the temperature dependence of the diffusion coefficients of protons obtained by the two techniques suggests that a vehicular type mechanism governs the transport. Solid state 23Na magic angle spinning (MAS) NMR was used to determine the state of sodium counterions in membranes equilibrated with 1 M sodium chloride solutions. The spectra exhibit two peaks, one narrow and another broad, corresponding, respectively, to isolated hydrated sodium ions and clustered sodium ions.