Synthesis, characterization, and redox reactivity of novel quinone-containing polymer

The synthesis of poly(vinyl hydroquinone), PV-HQ, via stable free radical p olymerization (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 mater ial ostensibly deposited (Gamma (theo)) increased the ratio Gamma (obs)/Gam ma (theo) (where Gamma (obs) and Gamma (theo) represent the measured and th e theoretical surface coverage values, respectively) drastically decreased, indicating that a significant fraction of the quinone sites are electroche mically inactive as the film thickness increases. This was attributed to a small electron transfer rate constant and to the fact that the electron tra nsfer is coupled to proton transfer, so the hydrophobicity of the polymer b ackbone 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 (Gam ma (obs) = 4.3 x 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 p H at a rate of 59 mV/pH unit up to pH 6. At higher pH values, the slope dec reased to ca. 30 mV/pH unit, suggesting a two-electron/one-proton reaction. The surface pK(a) value for the first deprotonation reaction was estimated to be 7.8.