Potential dependence of the conductivity of highly oxidized polythiophenes, polypyrroles, and polyaniline: finite windows of high conductivity

In situ measurements of the relative conductivity of polythiophenes, polyaniline, and polypyrroles as a function of electrochemical potential reveal that they have finite potential dependent windows of high conductivity. Further, the high conductivity is found where charge is injected or withdrawn from the polymer. The polymers studied, polyaniline and I-VI, are prepared by anodic polymerization onto microelectrode arrays of the appropriate monomer: thiophene (I), 3-methylthiophene (II), 3-phenylthiophene (III), 1-methyl-1{prime}-(3-(thiophene-3-yl)propyl)-4,4{prime}-bipyridinium (IV), 3,4-dimethylpyrrole (V), and N-methylpyrrole (VI). The use of a liquid SO{sub 2}/electrolyte medium as the electrochemical solvent makes it possible to define the window of high conductivity, because it allows the polymers to be reversibly oxidized to a greater extent than has previously been achieved. The conductivities of I-IV increase by at least 10{sup 6}-10{sup 9} when they are oxidized from neutral to the potential of maximum conductivity and then decrease by 10{sup 1}-10{sup 4} when they are further oxidized to the greatest extent possible without irreversible degradation in liquid SO{sub 2}/electrolyte.