Protonation and deprotonation behaviour of amine units in polyaniline

The structures of polyaniline salts chemically synthesized in HClO4 of varying concentrations have been examined by means of X-ray photoelectron spectroscopy. The results indicate that, although the imine units of the as-synthesized salt are preferentially protonated, a large proportion of the amine units are also protonated in the presence of a large excess of HClO4 on the surface of the salt particles. Protonated amine units are also observed when emeraldine base films cast from N-methylpyrrolidinone solutions are reprotonated by HClO4. The deprotonation behaviours of the salt synthesized in HClO4, the reprotonated film and polyaniline from the simultaneous oxidation and polymerization of aniline by Cu(ClO4)2.6H2O in acetonitrile are compared. It is found that the protonated amine units undergo deprotonation in aqueous media more readily than the protonated imine units and that both types of structures are stable when heated to 150°C in air.