Morphology, dielectric relaxation and conductivity of the novel polyurethanes with acid and ionic groups in the polyether segments

Abstract

The thermal transitions, microphase structure, local segmental and conductivity relaxation of the novel polyurethanes (PUs) based on the poly(tetramethylene glycol) as soft segments (SSs) and 4,4′-diphenylmethane diisocyanate-1,4-butane diol sequences of various length as hard segments (HSs) containing acid or ionic groups in SSs are studied by calorimetry, X-ray scattering and dielectric relaxation spectroscopy. The techniques used include differential scanning calorimetry, 173–473 K, wide-angle X-ray scattering, (WAXS) small-angle X-ray scattering (SAXS), broad band dielectric relaxation spectroscopy (DRS), 10 −2–10 6 Hz, and thermally stimulated depolarization currents (TSDC) techniques, 100–300 K. The peculiarities of microphase-separated structure (MSS) of the PUs such as composition of the microphases, periodicity of non-ionic PU MSS (about 17 nm), size of ionic aggregates in the ionomer (about 7 nm) and their distribution in the SS matrix were determined. The features of α-relaxation, conductivity relaxation and dc conductivity of the proton-conducting PU with acid groups and ion-conducting PU with ionic ones are found and discussed in connection with MSS of the PUs. The level of protonic dc conductivity increases with temperature up to 10 −5 S/m (323 K), whereas the ionic PU exhibits by about two decades lower conductivities, evidently due to ionic aggregation. Accordingly for the latter, apparent activation energy of the conductivity relaxation is considerably more than for the former.