Structure, thermal properties and ionic conductivity of polymeric quaternary ammonium salts (polyionenes) containing ethylene oxide and aliphatic chain fragments

Wide-angle X-ray scattering, small-angle X-ray scattering, dielectric spectroscopy and differential scanning calorimetry were employed to study the structure and relaxation properties of polyionenes based on ethylene oxide units of different length. It was found that the heterogeneity of the supramolecular structure is increasing with the length of the ethylene oxide fragments. Polyionenes with short ethylene oxide segments have an amorphous structure. The temperature dependence of the dc-conductivity of the samples with short chain ethylene oxide interionic fragments followed the Arrhenius law, indicating a thermally activated conductivity, which is not typical for polymeric electrolytes. On the other hand, the conductivity of samples with longer ethylene oxide segments (more than nine ethylene oxide units) has a Vogel-Tammann-Fulcher type temperature dependence. The samples showed a high conductivity even at temperatures lower than the glass transition temperature, Tg, due to their structure, which resembles the structure of an inorganic glass with ionic sites dissolved in an ordered matrix.