Structure–property relationships in proton conductors based on polyurethanes

Novel proton-conducting polyurethanes based on poly(tetramethylene glycol), with the protons being incorporated in the flexible soft segments, were prepared and their structure–property relationships were investigated. The structure and the morphology were studied by means of differential scanning calorimetry (DSC), and wide- and small-angle X-ray scattering (WAXS and SAXS). Molecular mobility and proton conductivity were measured by means of broadband dielectric relaxation spectroscopy (DRS, 10−2–109 Hz) and of thermally stimulated depolarisation currents techniques (TSDC, 77–300 K). Dc conductivity values, σdc, determined from ac conductivity and from complex impedance plots, are of the order of 10−5 S/m at 50°C, and decrease with increasing hard segment content of the polyurethanes. Their temperature dependence is described by Vogel–Tammann–Fulcher–Hesse (VTFH), suggesting that the conductivity mechanism is governed by the motion of the polymeric chains.