Effect of Mono and Multivalent Dopants on Electrical Conductivity and Solid-State 1H NMR Spectra of Polyaniline

Solid-state 1H nuclear-magnetic-resonance (NMR) measurements of polyaniline doped by HClO4, H2SO4, and H3PO4 were performed with magic-angle-spinning (MAS) methods to reveal the effects of protonation on chain arrangements and the electrical conductivity of polyaniline. In this study, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements were also carried out. Electrical conductivity measurements showed that polyaniline doped by HClO4 had a large conductivity as compared with polyaniline prepared with H2SO4 and H3PO4 dopants. In addition, 1H MAS NMR spectra revealed that the ratio of -NH+= and -NH2+- sites increased with increasing dopant concentration in the polymers. The linewidths of the 1H MAS NMR signals of polyaniline doped by HClO4 were similar to those polymerized from aniline-d5 (C6D5NH2) in HClO4 solution. Based on this result, polyaniline can undergo fast motions in the solids. NMR, SEM and XRD spectra suggest that multivalent dopants of H2SO4 and H3PO4 construct polymer blocks in the solids and that the blocks contribute to their low electrical conductivities.