IONIC AND ELECTRONIC CONDUCTIVITY OF POLY-(3-METHYLPYRROLE-4-CARBOXYLIC ACID)

The electronic and ionic conductivities of poly-(3-methylpyrrole-4-carboxylic acid) have been measured in situ by twin electrode voltammetry and impedance spectroscopy, respectively. The electronic conductivity of this polymer, ca. 10(-2) (OMEGA cm)-1, is about 10000 times higher than its ionic conductivity, allowing application of a simple transmission line circuit to model ion transport within the polymer. Under almost all conditions investigated the impedance response was similar to that of a transmission line and unambiguous measurements of the polymer's ionic conductivity could be obtained. The variation of this conductivity with solvent, electrolyte concentration, cation size, and potential has been explained in terms of a two-phase model in which the ionic resistance of the polymer is a series combination of the resistance of each phase. One phase appears to be pores containing electrolyte solution of similar composition to the bulk electrolyte. The other is a polymer phase which exhibits a cation dependent ionic conductivity, and therefore may be self-doped.