Structure of chemically prepared poly-(para-phenylenediamine) investigated by spectroscopic techniques

The structure of chemically prepared poly-p-phenylenediamine (PpPD) was investigated by Resonance Raman (RR), FTIR, UV-VIS-NIR, X-ray photoelectron (XPS), X-ray Absorption at Nitrogen K edge (N K XANES), and Electron paramagnetic Resonance (EPR) spectroscopies. XPS, EPR and N K XANES data reveal that polymeric structure is formed mainly by radical cations and dication nitrogens. It excludes the possibility that PpPD chains have azo or phenazinic nitrogens, as commonly is supposed in the literature. The RR spectrum of PpPD shows two characteristic bands at 1527 cm−1 and 1590 cm−1 that were assigned to νCN and νCC of dication units, respectively, similar to polyaniline in pernigraniline base form. The presence of radical cations was confirmed by Raman data owing to the presence of bands at 1325/1370 cm−1, characteristic of νC-N of polaronic segments. Thus, all results indicate that PpPD has a doped PANI-like structure, with semi-quinoid and quinoid rings, and has no phenazinic rings, as observed for poly-o-phenylenediamine.