Dynamics of sulfonated polystyrene ionomers using broadband dielectric spectroscopy

The dynamics of sulfonated polystyrene ionomers were investigated by using broadband dielectric relaxation spectroscopy. Dynamic mechanical analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, and small-angle X-ray scattering were employed in a complementary role. Sulfonated polystyrene ionomers were prepared from the precursor sulfonic acid polystyrene, having 1 and 7 mol % sulfonic acid, by exchanging the protons of the acid functionality with Na, Cs, and Zn cations. Three dielectric relaxations were observed above the glass transition temperature: the segmental α process and relaxations associated with Maxwell-Wagner-Sillars interfacial polarization and electrode polarization. The low-frequency broadening of the a transition is related to constraints imposed by the ionic aggregates. A relaxation in the glassy state was observed for the precursor sulfonic acid polystyrene and ionomers and attributed to the local motion of sulfonated phenyl groups. The relaxation strengths of the β processes of the ionomers were suppressed by interaction with the cations that create physical cross-links, and the relaxation times decreased with increasing strength of the electrostatic interaction of the ion pairs.