Simultaneous ionic and electronic conductivity in polymeric materials

Pyrrole and 3-(3,6-dioxaheptyl)pyrrole were polymerized in the presence of an oligo(oxyethylene monomethylether) sulfonate (DPPEO = 17) with ammonium peroxydisulfate as an oxidizing agent and dry chloroform as a solvent. The oligo(oxyethylene) sulfonate acted as a phase transfer agent and also became incorporated into the polymer as a counter ion. The polymers were obtained as gel-like particles that could be easily dispersed in organic solvent and could be doped with lithium triflate to enhance the ionic conductivity of the electronically conductive materials. DSC and X-ray measurements showed a glass transition (T-g) in all samples at around -40 degrees C which is related to the dynamics of the EO segments. In addition, the system composed of polypyrrole with oligo(oxyethylene) sulfonate counter ions showed partial crystallinity and a melting transition at 34 degrees C. Conductivity was explored by impedance spectroscopy with regard to frequency and temperature dependence. The data could be evaluated in the coordinates of an Arrhenius plot as the sum of two Arrhenius functions in all cases. Although one Arrhenius-type function was sufficient to describe the temperature profile of the conductivity below T-g, a second term needed to be added at T > T-g. The absolute values of conductivity were also dependent on the level of doping with lithium triflate. These phenomena were interpreted as a contribution of ionic conductivity by the lithium ions to the electronic conductivity, which comes about from the oxidation state of the polypyrrole backbone.