Initial states in the electropolymerization of aniline and p-aminodiphenylamine as studied by in situ FT-IR and UV-Vis spectroelectrochemistry

The study on the very first stages of electrochemical polymerization of aniline and p-aminodiphenylamine (p-ADPA) on electrodes by in situ FT-IR/ATR and UV-Vis transmission techniques is presented. The in situ FT-IR/ATR measurements indicate the highest polymer growth rate during the reversed cathodic potential scan in potentiodynamic electropolymerization. In this scan direction the p-ADPA radical is formed in a less anodic potential region by symproportionation of the soluble oxidized dimer N-phenyl-quinonediimine with p-ADPA formed by re-reduction. The resulting radical formed by symproportionation causes the polymer growth. The radical cations form the tetrameric Willstنtter blue and red imine by dimerization and further oxidation. Therefore, the main step in polymer deposition is the radical reaction of p-ADPA. By further reactions of the first oligomers, insoluble higher oligomers are formed and deposited on the electrode. The preferred occurrence of these reactions is the reason for the more intense polymer growth by cycling of the potential in comparison to potentiostatic methods. Comparative studies of the p-ADPA polymerization were done under the same conditions. The comparison of FT-IR vibration modes of PANI and polymerized p-ADPA shows significant structural differences of both polymers. By FT-IR and UV-Vis spectroscopy it is shown that the main structure of polymerized p-ADPA is the aniline tetramer Willstنtter blue/red imine.