Association of electroactive counterions with polyelectrolytes. 2. Comparison of electrostatic and coordinative bonding to a mixed polycation-polypyridine

Abstract

A soluble polysiloxane containing 4,4'-bipyridine as a singly quaternized pendant group was synthesized and allowed to interact with Fe(CN)_6^(4-), Fe(CN)_5(OH_2)^(3-), and Ru(edta)OH_2^- as counterions. The electrochemical responses (formal potentials and mass-transfer-limited oxidation or reduction currents) of the electroactive counterions were utilized to evaluate diffusion coefficients and equilibrium binding constants. The latter were also measured by equilibrium dialysis. The moderate agreement between the equilibrium constants obtained by the two independent methods lent support to the general procedures employed in analyzing the electrochemical data, although some of the assumptions required for the data analysis may not be fully justified. The results obtained indicate that the polyelectrolyte-counterion binding equilibrium is static rather than dynamic on the electrochemical time scale of a few hundred milliseconds.

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