EFFECT OF QUATERNIZATION ON ELECTRON-DIFFUSION COEFFICIENTS FOR REDOXHYDROGELS BASED ON POLY(4-VINYLPYRIDINE)

The effect of partial quarternization of pyridine rings on the electro n transport characteristics in redox-conducting hydrogels of cross-lin ked poly(4-vinylpyridine), partially complexed with [Os(bpy)(2)Cl](+/2 +), was studied using steady state voltammetry at interdigitated array (IDA) electrodes. The apparent electron diffusion coefficients, D-app , and their pH dependence were mapped for redox hydrogels varying in t he (a) extent of quaternization of their pyridine rings, (b) nature of quaternizing groups, (c) degree of cross-linking, and (d) loading wit h [Os(bpy)(2)Cl](+/2+) centers. In gels made with polymers that were n ot quaternized, high electron diffusion coefficients were observed onl y when the pyridine rings were protonated. However, in gels made with substantially quaternized redox polymers, high and pH independent elec tron diffusion coefficients were observed. When one-half of the pyridi ne rings were quaternized, the electron diffusion coefficients were co mpletely independent of pH and reached a value of 3.9 x 10(-8) cm(2) s (-1). Excessive cross-linking decreased the electron diffusion coeffic ients. At a fixed level of quarternization the electron diffusion coef ficients increased with the density of redox centers. This increase re sulted, however, from the added charge; when the density of electrosta tic charge per macromolecule was fixed, i.e., when the degree of quate rnization was increased to compensate for a lower loading of redox cen ters, the electron diffusion coefficients were the same. It was conclu ded that the rate of electron transport is determined by the segmental motion of the polymer chains in cross-linked redox hydrogels.