THERMOCHEMISTRY AND KINETICS OF CHEMICAL POLYMERIZATION OF ANILINE DETERMINED BY SOLUTION CALORIMETRY

The thermochemistry and reaction kinetics of oxidative chemical polymerization of aniline (AN) with ammonium peroxydisulfate (APS) in various aqueous acids, concentrations, and oxidant/aniline ratios are reported. The polymerization was found to be a highly exothermic reaction leading to the formation of the emeraldine form of polyaniline with an enthalpy change of -105 kcal/mol of AN when aniline is in excess. Overoxidation with APS in excess caused the formation of higher oxidation states of polyaniline as well as polymer chain hydrolysis and chlorine substitution. The reaction kinetics were found to be different between polymerizations in highly acidic and relatively neutral pH's, though the reaction enthalpy was the same. In situ UV spectra of the polymerization showed that emeraldine was rapidly formed in acidic media, where as low molecular weight products were produced in relatively neutral media. The polyaniline produced using excess aniline and highly acidic media showed the highest conductivity. An empirical relationship was found that relates the reaction induction period to the starting concentration of aniline in aqueous HCl solutions. A strong dependence of the induction period on the nature of the acid used in the polymerization was also found.