Thermal stability of chemically synthesized polyaniline

Abstract

Two polyanilines (PAns) were prepared by utilizing two different oxidizing agents, ammonium persulfate (APS) and ammonium dichromate (ADC) in aqueous toluene sulfonic acid (TSA). The thermal stability of the resulting as-prepared PAns was evaluated in both air and nitrogen, and the results were compared. With ADC, TSA-doped PAn was obtained, while with APS, PAn doped with sulfuric acid was obtained. For the letter, the dopant (sulfuric acid) originated from the APS during the oxidation of aniline. At a temperature between 100 and 180 °C in both air and nitrogen atmosphere, the conductivity of PAn prepared from APS decreases monotonically with time. The decreasing conductivity is governed approximately by first-order kinetics, and its dominant cause is the addition of sulfate to the PAn aromatic ring. However, the conductivity of PAn prepared using ADC increases with aging time at 130 °C regardless of the atmosphere and, at 160 °C, it shows a peak with aging time. This behavior is explained in terms of a change in the arrangement of the polyaniline chain.