Novel polyurethane ionomers based on poly(ethylene oxide) with nonionic hard segments of varying length and flexible segments containing alkali ions (or protons) have been prepared and their structure-property relationships have been investigated. Differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) were employed for structural investigation, whereas molecular mobility and ionic conductivity were studied by means of thermally stimulated depolarization currents (TSDC) techniques and of broadband (10(-2)-10(9) Hz) dielectric relaxation spectroscopy (DRS). The ionomers are characterized by the coexistence of the segment microphase separation and the ionic group segregation morphologies. Crystallization is observed at low hard segment contents (melting at about 305 K), the tendency for crystallization decreasing upon hard segment extension and decreasing upon neutralization. Values of ionic conductivity are in the range of 10(-4) S/m at 323 K, the conductivity in the amorphous polyurethanes bring governed by the motion of the polymeric chains.