Exploration of the morphological transition phenomenon of polyaniline from microspheres to nanotubes in acid-free aqueous 1-propanol solution in a single polymerization process

In Situ Infrared Spectroscopy of Oligoaniline Intermediates Created under Alkaline Conditions

The progress of the oxidation of aniline with ammonium peroxydisulfate in an alkaline aqueous medium has been monitored in situ by attenuated total reflection (ATR) Fourier transform infrared spectroscopy. The growth of the microspheres and of the film at the ATR crystal surface, as well as the changes proceeding in the surrounding aqueous medium, are reflected in the spectra. The evolution of the spectra and the changes in the molecular structure occurring during aniline oxidation in alkaline medium are discussed with the help of differential spectra. Several processes connected with the various stages of aniline oxidation were distinguished. The progress of hydrolysis of the aniline in water and further an oxidation of aminophenol to benzoquinone imines in the presence of peroxydisulfate in alkaline medium have been detected in the spectra in real time. The precipitated solid oxidation product was analyzed by mass spectrometry. It is composed of oligomers, mainly trimers to octamers, of various molecular structures incorporating in addition to aniline constitutional units also p-benzoquinone or p-benzoquinoneimine moieties.

Polyaniline: The infrared spectroscopy of conducting polymer nanotubes (IUPAC Technical Report)

Polyaniline (PANI), a conducting polymer, was prepared by the oxidation of aniline with ammonium peroxydisulfate in various aqueous media. When the polymerization was carried out in the solution of strong (sulfuric) acid, a granular morphology of PANI was obtained. In the solutions of weak (acetic or succinic) acids or in water, PANI nanotubes were produced. The oxidation of aniline under alkaline conditions yielded aniline oligomers. Fourier transform infrared (FTIR) spectra of the oxidation products differ. A group of participants from 11 institutions in different countries recorded the FTIR spectra of PANI bases prepared from the samples obtained in the solutions of strong and weak acids and in alkaline medium within the framework of an IUPAC project. The aim of the project was to identify the differences in molecular structure of PANI and aniline oligomers and to relate them to supramolecular morphology, viz. the nanotube formation. The assignment of FTIR bands of aniline oxidation products is reported.