Synthesis, Characterization, and Redox Reactivity of Novel Quinone-Containing Polymer

The synthesis of poly(vinyl hydroquinone), PVHQ, via stable free radical polymerization (SFRP) to give a low-dispersity (1.5) material is described. The electrochemical properties of the resulting material deposited as films onto glassy carbon electrodes have been investigated by cyclic voltammetry. In aqueous acetic acid solution, it was found that as the amount of material ostensibly deposited (Γ theo ) increased the ratio Γ obs /Γ theo (where Γ obs and Γ theo represent the measured and the theoretical surface coverage values, respectively) drastically decreased, indicating that a significant fraction of the quinone sites are electrochemically inactive as the film thickness increases. This was attributed to a small electron transfer rate constant and to the fact that the electron transfer is coupled to proton transfer, so the hydrophobicity of the polymer backbone might adversely affect the accessibility of protons. Using Laviron's theory, the electron-transfer rate constant and the transfer coefficient were determined to be 2.1 s - 1 and 0.5, respectively, for a PVHQ film (Γ obs = 4.3 × 10 - 10 mol cm - 2 ) on a glassy carbon electrode in 0.10 M acetic acid solution. The formal potential of the PVHQ film shifted with pH at a rate of 59 mV/pH unit up to pH 6. At higher pH values, the slope decreased to ca. 30 mV/pH unit, suggesting a two-electron/one-proton reaction. The surface p K a value for the first deprotonation reaction was estimated to be 7.8.