Complex impedance and multifrequency ²³Na NMR study of poly (propylene oxide) complexed with NaB (C₆H₅)₄

Complex impedance and multifrequency ²³Na nuclear magnetic resnoance (NMR) measurements on a poly (propylene oxide): sodium tetraphenylborate, PPO₈NaB(C₆H₅)₄, solid polymer electrolyte, with a composition of eight ether oxygens per sodium, are reported. The NMR linewidths are found to be second-order quadrupole broadened, thus indicating low site-symmetry for the Na⁺ ions. The title compound exhibits some interesting differences in properties compared to other PPO-Na salt complexes, including an anomalously low value of the stretched exponential parameter ß_se (obtained in fits to electric modulus data), an unusually high glass transition temperature (T_g=306 K), and sub-T_g line narrowing of lower frequency ²³Na resonances. This last phenomenon is attributed to strong interaction between the Na⁺ ions and their large [B(C₆H₅)₄]^- counterions caused by the localization of the [B(C₆H₅)₄]^- anions in weak interactions with the polymer chains which, in turn, leads to the elevated glass transition temperatures.