Synthesis and characterization of polymerized 3-aminophenyl phosphonic acid prepared in the presence of p-phenylenediamine

Conducting polymers can be exploited for use in many innovative technologies, such as biosensors, chemical sensors, electrochromic displays and flexible electronic devices. In general, the conductive state of a conducting polymer is generated by the partial oxidation or reduction of the π-conjugated system in the polymer backbone via a chemical or electrochemical doping process. The doped conducting polymer possesses charge carriers that can be electrically delocalized to show electrical conductivity and other electroactive properties. Among various conducting polymers, polyaniline becomes one of the most widely investigated because of its ease of synthesis and good environmental stability. Briefly, the emeraldine base form of polyaniline can undergo protonic doping to become a conductive emeraldine salt. With the variation in the oxidation state of the polymer backbone, the polymer can distinctively exist as leucoemeraldine, emeraldine or pernigraniline. Self-doped PANI contains intramolecular dopant acid groups, such as sulfonic acid, boronic acid and carboxylic acid. Therefore, the covalently attached acid groups of the PANI backbone can dope the polymer chain without the addition of an external dopant acid. In this study, polymerization of 3-aminophenyl phosphonic acid in the presence of p-phenylenediamine was synthesized by the oxidative chemical polymerization method in several different aqueous media. After dissolving 3-aminophenyl phosphonic acid in deionized water, 1M aqueous HCl solution, or pH 3 buffer solution containing a trace amount of p-phenylenediamine, the oxidant, ammonium peroxydisulfate (APS), was added to the solution. After the reaction was initiated, the change in the color of the reaction media, as well as precipitation of solid materials, was observed. After the reactions were completed, the whole reaction mixtures were collected and dialyzed. The obtained materials were then characterized using a scanning electron microscope (SEM), UV-Vis-NIR spectrometer, fourier transform infrared spectroscopy (FTIR) and four-point probe apparatus. The SEM images showed that the polymerized 3-aminophenyl phosphonic acid appeared grainy and agglomerated. The sheet resistance measurement by the four-point probe method indicated that the material prepared in 1M aqueous HCl solution, deionized water or pH 3 buffer solution was non-conductive. The above preliminary results suggest that the pH of the aqueous medium in which the polymerization of 3-aminophenyl phosphonic acid takes place can affect the properties of the final solid products, indicating that self-doped polyaniline with phosphonic acid can be used for applications as photon exchange membranes of fuel cells or electrochromic materials.