A non-isothermal cell was employed to determine the reaction entropies DELTAS(rc)-degrees of several electroactive transition metal complexes in aqueous solution and in Nafion(R) and poly(styrenesulphonate) coatings deposited on glassy carbon electrode surfaces. In contrast with earlier results, the DELTAS(rc)-degrees values recorded indicated that the ionic environments are significantly different in these media and that electron exchange rates are lower in the polymers than in aqueous solution. Differential Gibbs energies, enthalpies and entropies corresponding to the distribution of the oxidized and reduced components of each redox couple between the polymer phases and the solution were also evaluated.