In situ determination of aniline polymerization kinetics through near-infrared spectroscopy

This article describes a method for the determination of kinetic constants in aniline polymerizations performed in the presence of dodecylbenzene sulfonic acid. The procedure was based on the measurement of light absorbances at 668 and 1026 nm. The absorption at 668 nm is related to pernigraniline formation and is ordinarily used for ultraviolet-visible kinetic studies. The absorption at 1026 nm is related to the second overtone of the N---H bonds, which may be used to monitor the aniline consumption along the reaction time. Tzou and Gregory's empirical reaction model was used as a reference for kinetic studies. The best fits were obtained when the kinetic constants were evaluated at 1026 nm because of the lower noise/signal ratio in this spectral region and the smaller sensitivity to the pernigraniline/emeraldine transition during the last stages of the polymerization. The remarkable innovation supplied by this study is the possibility to study aniline polymerizations in situ in realistic reaction conditions, which will allow the use of concentrated monomer solutions, large reaction volumes, efficient cooling conditions, and agitation.