Spectroscopic investigation on polymer films obtained by oxidation of o-phenylenediamine on platinum electrodes at different pHs

An investigation on the structure of poly(o-phenylenediamine) (PPD) films, obtained by electropolymerization of oPD (1,2-diaminobenzene) on platinum at different pH values, was performed by X-ray Photoelectron Spectroscopy (XPS). XPS could be used as a "bulk" technique for PPD films analysis, due to their extremely low thickness. The presence of different functionalities, like primary/secondary aminic, iminic and, as minor species, oxygenated groups (carbonyl, oximes) was suggested by curve fitting of carbon (C1s) and nitrogen (N1s) XP spectra. The use of chemical derivatization reactions (CD-XPS) confirmed the presence of primary aminic and hydroxy groups, showing that NH2 groups are present in the PPD structure even at low pH values, though their amount increases on increasing the pH of polymerization. Optical spectroscopy in the visible region was also performed on the electrolytic solutions at the end of polymerization, suggesting a higher conjugation of the oPD oligomers at low pH, which indirectly confirms XPS findings on the presence of NH2 groups in the polymer.