Processing of Polyanilines

Abstract

The term polyaniline represents a family of polymers which are inter-convertible by acid/base and oxidation/reduction reactions. Of particular interest from the standpoint of processing are the half oxidized forms-emeraldine base and the emeraldine salt. The emeraldine base is the neutral form with a conductivity lower than 10⁻¹⁰ S/cm. It undergoes insulator to metal transition on treatment with protonic acids yielding emeraldine salt or the conducting form of polyaniline with a conductivity of 1–10 S/cm. In its conductive form, polyaniline is a dark green powder and is infusible and insoluble in most solvents. However it is claimed to be soluble in concentrated acids such as sulfuric acid, methane sulfonic acid, formic and acetic acids. The emeraldine base form is soluble in a wide variety of solvents such as N-methyl pyrrolidone, dimethyl formamide, dimethyl sulfoxide and the like. The chemistry and physics of polyanilines has been widely discussed in the literature [1–4]. The infusibility and insolubility of the doped polymer has been a real drawback for processing and potential applications for this class of polymer. The solubility of emeraldine base form of polyaniline has been exploited as a processing avenue and a number of prototype products have been demonstrated. Nevertheless, the harsh nature of the solvents used in the process may pose an environmental threat for processing of polyanilines on a commercial scale. Furthermore, the articles thus processed need to be doped in order to render them conductive; this may lead to some practical problems.