Simple synthesis of water-soluble conducting polyaniline

A water-soluble externally (HCl)-doped conducting polyaniline (ED-SPAN) is prepared by such a simple synthetic method that emeraldine salts are sulfonated by chlorosulfonic acid in dichloroethane at 80 degrees C and subsequently hydrated in water at 100 degrees C. Sulfonating any emeraldine salts (counter anion X- = Cl-, SO42-, and BF4-) or emeraldine base results in the production of HCl-doped sulfonated polyaniline, where HCl dopant from hydrolysis of chlorosulfonic group exchanges with the original dopant. The degree of sulfonation, namely, sulfur-to-nitrogen (S/N) ratio, can be controlled by adjusting the amount of chlorosulfonic acid. With increasing S/N ratio from 0.65 to 1.3, the solubility in neutral water increases from 22 to 88 g/l and the four-probe conductivity for a compressed pellet decreases from 0.023 to 1.7 X 10(-5) S/cm, showing sulfonation-induced undoping. (C) 1998 Elsevier Science S.A. All rights reserved.