ASSOCIATION OF ELECTROACTIVE COUNTERIONS WITH POLYELECTROLYTES .6. ELECTROSTATIC AND COORDINATIVE BINDING OF RU-3+ 2+ CENTERS TO A COPOLYMER OF ACRYLIC-ACID AND ACRYLONITRILE/

A random copolymer of acrylic acid and acrylonitrile was prepared in w hich the functionality on the polymer chain consisted of 93% carboxyli c acid groups, 4.1% nitrile groups, and 2.9% acid anhydride groups. Th e nitrile groups were used to coordinate RU(NH3)(5)(2+) centers to the copolymer. The anionic carboxylate groups produced at pH values above similar to 3.5 were used to bind Ru(NH3)(6)(3+) counterions to the re sulting polyanionic copolymer. The electrochemical oxidation or reduct ion of the two redox centers bound to the copolymer were used to estim ate diffusion coefficients for the copolymer. Reasonable agreement was obtained between the values obtained from both electroactive redox gr oups. The diffusion coefficient exhibited a strong dependence on pH th at reflected changes in the structure of the copolymer as it was conve rted from its neutral to its polyanionic form. The rate of the reactio n between the Ru(NH3)(5)OH22+ complex and the nitrile groups of the co polymer increased significantly with pH because electrostatic binding of the cation to the polyanionic copolymer increased the concentration of the complex in the vicinity of the nitrile groups. Adsorption of t he copolymer on the surface of the electrodes interfered with the oxid ation of Ru(NH3)(5)(2)+ groups coordinated to the dissolved copolymer but not with Ru(NH3)(6)(3+) counterions electrostatically bound to the polyanion. A possible explanation for the contrasting behavior is sug gested.