Protonation, sol formation and precipitation of poly- and oligoanilines

Raman spectrometry, UV–visible–near IR and attenuated total reflection IR absorptions are used to analyze the protonation of the emeraldine form of the phenyl/ — NH2 end-capped BQBBa tetramer and of the phenyl/ — NH2 end-capped (BQBB)4a hexadecamere in strong (H2SO4 or HCl), intermediate (CH3COOH) and weak (CH3OH) acids. Evolution of the pristine solution with aqueous dilution and time is analyzed in order to understand the formation of a sol of nanofilaments, which agglomerate and finally precipitate. Water in an acidic solution favors the precipitation of the corresponding emeraldine salt material, i.e. increases the degree of aggregation of the oligomeric species and the aromatic behavior of the rings. The secondary doping effect consists in intercalation of water molecules in the highly aggregated (paramagnetic) species, strongly bound to the oligomeric units and whose removal is always accompanied by elimination of the protonating agent (primary doping). The role of interchain interactions in charge carrier mobility appears more important than that of intrachain behavior. Copyright  2003 John Wiley & Sons, Ltd.