Sulfonic Acid Ring-Substituted Polyaniline, A Self-Doped Conducting Polymer

Sulfonic acid ring-substituted polyaniline has been synthesized and characterized by elemental analysis, FTIR, UV-vis and electron spin resonance spectroscopy. Approximately 50% of the total number of phenyl rings in the polymer are mono-substituted by -SO− 3 groups. Without external doping, the ring-sulfonated polyaniline has a conductivity of ∼0.03 S/cm; it is therefore a “self-doped” conducting polymer. The water soluble sodium salt of the ring-sulfonated polyaniline is an insulator and can be reversibly converted back to the self-doped conducting form by treatment with aqueous acid.