Polyaniline: a new concept in conducting polymers

The analytically pure base form of polyaniline, , corresponding to the emeraldine oxidation state is converted from an insulator (σ 10−10S/cm) to a metal (σ 5 S/cm) by treatment with 1M aqueous HCl to form the corresponding salt, emeraldine hydrochloride, . This involves a new type of doping of a conducting polymer in that the number of electrons associated with the polymer undergoes no change during the protonic acid doping process. The metallic emeraldine hydrochloride is believed to be a delocalized poly(semiquinone radical cation) having a polaron conduction band, with most of the positive charge residing on the nitrogen atoms. It exhibits a finite density of states at the Fermi energy.