Distribution of redox potentials in arylamine derived polymers

D. POSADAS; M. FONTICELLI; M. J. RODRÍGUEZ PRESA; M. I. FLORIT

Poraj

Workshop; NATO Advanced Research Workshop on Electrochemistry of Electroactive Polymer Films WEEPF-2000; 2000

International Society of Electrochemistry

The apparent standard redox potential of arylamine derived polymers can be characterized by a distribution function over a certain range of potentials. This is measured, by linear sweep voltammetry, for two arylamine derived polymers: a conducting one as poly-o-toluidine (POT) and a redox one such as poly-o-aminophenol (POAP), in different electrolytic media. For the former, the distribution function depends on the solution pH and anion nature and concentration. Also, it is shown that POT expands and contracts during the oxidation reduction cycles. The statistical mechanics description for the reversible redox switching of immobilised redox couples is considered within the framework of the Bragg-Williams approximation. Also, it is presented a model considering the oxidized and reduced units of the polymer having different length. From it, an expression for the apparent standard potential of the polymer, including a mechanical work of expansion/contraction, is obtained. The model represents very well the distribution of apparent formal redox potentials for both polymers studied here. Furthermore, the true formal potential results dependent on the pH of the external solution and very slightly dependent on its ionic strength. The analysis of the results allow us to conclude that the number of redox centers associated with the expanding units is one for POT and two for POAP.