Synthesis of highly sulfonated polyaniline

An alternative approach to synthesize sulfonated polyaniline (SPAN) is described. This route results in higher sulfur-to-nitrogen ratio (SN ratio up to about 34 compared to 12 for the original route) and higher yield (about 70%). Compared to the SPAN prepared via the previous route, the new SPAN has higher solubility (approximately double), higher d.c. conductivity (about one order higher), nearly pH- independent d.c. conductivity in the region of 0 ⩽ pH ⩽ 14 (while emeraldine salt has a sharp drop in d.c. conductivity to an insulator at pH ∼ 3 and the SPAN made via the previous route becomes semiconducting at pH ∼ 7.5), a different pH dependence of the cyclic voltammogram spectrum, and other novel properties. The relationship of these improved physical properties to the change of synthetic route is suggested.