Ion transport in polyacetylene ionomers

Ion transport in cationically and anionically functionalized polyacetylene ionomers, PA(C) and PA(A), respectively, was investigated by analyzing the impedance responses of thin film Au parallel to ionomer parallel to Au sandwich configurations. Samples were measured over a frequency range of 10(-2)-10(6) Hz and a temperature range of 298-398 K. Electrode polarization at low frequencies and dispersion due to ion hopping at higher frequencies were observed. The impedance data were analyzed first without the reliance on a specific model, then through equivalent circuit modeling, to estimate the dc (bulk) ion conductivity sigma(0), ion hopping rate omega(h), and dielectric constant of the polymer matrix. The dispersive ion hopping conduction was best modeled by a distributed process involving the Kohlrausch-Williams-Watts stretched exponential decay function. The ionic conductivity of both ionomers exhibited an Arrhenius dependence on temperature with similar activation energies: 0.94 eV for PA(C) and 0.97 eV for PA(A). At 308 K, the ionic conductivity of PA(C) was measured to be 1.1x10(-11) S/cm while that of PA(A) was measured to be 1.3x10(-12) S/cm. The dielectric constant for the polymer matrix in the absence of ionic polarization was found to be epsilon(D)=4.5 for PA(C) and epsilon(D)=4.2 for PA(A) at 308 K. The assignment of the conductivity to ionic processes implies an extremely small intrinsic electronic conductivity in these polymeric semiconductors.