THE ANION-SPECIFIC EFFECT IN THE OVEROXIDATION OF POLYANILINE AND POLYINDOLINE

The irreversible degradation (overoxidation) of polyaniline and polyindoline has been investigated in the presence of different anions incorporated in the films. In-situ conductivity, electron spin resonance and UV-Vis measurements together with cyclic voltammetry were performed to investigate the various properties of the two closely related polymers as a function of both the electrode potential and the nature of anions. When the upper potential limit is adjusted adequately to avoid irreversible degradation at higher potentials in polyaniline and polyindoline, the behavior of the polymers is not affected by the exchange of the anions ClO4-, SO42-, Cl- and NO3-. However, beyond these potential limits, the polymer properties develop quite differently depending upon whether perchlorate or sulfate ions are available for charge compensation. In the presence of sulfuric, nitric and hydrochloric acid both polymers are subjected to rapid electrochemically induced irreversible degradation, whereas with perchloric acid the electroactive properties of the polymers are still present after the measurements have been performed. In this sense polyaniline and polyindoline have much in common, implying a similar structural configuration of the newly synthesized polyindoline compared with the well-known polyaniline. In view of the results achieved, a tentative explanation for the anion-specific effect is proposed. The effect seems to emerge from the anion-influenced interaction between the charge carriers of the polymers, identified primarily as bipolarons, and the different anions incorporated in the polymer matrix for charge compensation.