Polypyrrole oxidation: Kinetic coefficients, activation energy and conformational energy

Polypyrrole films after reduction for a constant time at rising cathodic potentials were used as initial states for subsequent oxidation. The potentiostatic oxidation occurs, at intermediate times, under chemical kinetic control. Rate coefficients (k), activation energies (Ea) and reaction orders were determined from experimental results. Otherwise than most of the electrochemical reactions, k and Ea change with the reduction potential. The obtained experimental results follow the evolution predicted by the Electrochemically Stimulated Conformational Relaxation model, which states that rising reduced, shrinked and conformational packed states of polymeric conformations are obtained by cathodic prepolarizations at increasing cathodic potentials. Slower oxidation rates, requiring higher activation energies, were obtained when rising packed conformations were used as initial states for the oxidation. The activation energy includes two components: the constant chemical activation energy and the conformational packing energy that increases linearly with the reduction potential. So, k and Ea quantify the conformational packing state of reduced polymeric chains, opening new possibilities for the interaction between Electrochemistry and Polymer Science.