INFLUENCE OF HYDROLYSIS ON THE CHEMICAL POLYMERIZATION OF ANILINE

The influence of hydrolysis on the process of oxidative polymerization of aniline was evaluated through the effect of polymerization temperature on the yield of polyaniline (PANI) in different pH regions where the polymerization took place. The synthesis parameters were chosen based on the dependence of the polymerization and hydrolysis processes on the pH of the medium, and considering the opposing thermal effects of the two processes (exothermic polymerization and endothermic hydrolysis). The yield of PANI was evaluated from the conductivity of composite films cast from aqueous dispersions of PANI prepared by chemical oxidative polymerization of aniline using poly(vinyl alcohol-co-acetate) as a steric stabilizer. It was found that the influence of hydrolysis is most pronounced in slightly acidic (pH>4) and strongly acidic (pH < 1.5) media. This imposes the requirement for the polymerization of aniline to be carried out at low temperature (0-5-degrees-C) in order for hydrolysis to be suppressed. When the initial stage of polymerization takes place at 4 < pH < 1.5, hydrolysis does not play a significant role and polymerization proceeds with a high yield irrespective of the temperature changes.