A study of the kinetics of polymerization of aniline using proton NMR spectroscopy

The polymerization of aniline has been studied by monitoring monomer depletion using proton NMR spectroscopy. For precipitation polymerization at 298 K using Na2S2O8 as oxidant an induction period of several minutes was observed, followed by relatively rapid polyaniline formation. In contrast, much slower polymerization was found using KIO3 as oxidant. In both cases there is a significant residual NMR signal, even though a stoichiometric amount of oxidant was used. This was attributed to soluble aniline oligomers rather than unreacted aniline monomer. At 278 K the rate of polymerization is markedly slower for both oxidants. No significant differences were observed between the rates of precipitation polymerization and dispersion polymerization using a reactive poly(ethylene oxide)-based stabilizer. Faster reactions were observed when aniline was polymerized in the presence of ultrafine 20 nm silica particles to form polyaniline-silica colloidal nanocomposites. Polymerization was slower when aniline was polymerized in the presence of surfactant micelles to form surfactant-stabilized polyaniline particles; this is probably due to the high viscosity of the reaction solution.