Dispersion polymerization of aniline in different media: A UV-visible spectroscopic and kinetic study

The course of dispersion polymerization of aniline using ammonium peroxodisulfate (APS) as initiator oxidant and poly(vinyl alcohol) as stabilizer in different media, viz., water (1 M HCl), water (pH = 2.41, [aniline] equivalent to [HCl]), and aqueous ethanol(1 M HCl), was followed spectrophotometrically. It: was found that the absorption peak positions for the pernigraniline salt change markedly with change in acidity and [APS]/[aniline] ratio. The spectral shape also changes greatly when water is replaced by aqueous ethanol. The evolution of the spectra with time was used to generate rate curves which reveal the autocatalytic nature of the reaction. The activation energies of the reaction in the various media were evaluated for both the induction period and the polymerization period using the inverse of the times of these periods as representing average rates for the periods, respectively. The activation energies increase with decrease in medium polarity and/or acidity. These variations have been discussed.