title: Characterization of reaction intermediate aggregates in aniline oxidative polymerization at low proton concentration.
abstract: Aggregates of reaction intermediates form during the early stages of aniline oxidative polymerization whenever the initial mole ratio of proton concentration to aniline monomer concentration is low ([H(+)](0)/[An](0) <or= 1.0). Detailed characterization is carried out on those aggregates. The intermediate aggregates show a UV-Vis absorption peak at around 410 nm when dispersed in aqueous solution, whereas the peak is centered on 370 nm when dissolved in an organic solvent such as N-methylpyrrolidone. The electronic band gap decreases when the intermediates aggregate to form a solid, and thus, the absorption peak is red-shifted. Gel permeation chromatography (GPC) shows the aggregates contain a major low molecular weight peak with a long tail. The oligoanilines with low molecular weights consistently show a UV-Vis absorption peak at around 370 nm. Mass spectrometry confirms that the intermediate aggregates contain mainly a component with mass number 363 (M + H(+)), likely a tetramer. UV-Vis, GPC, mass spectrometry, NMR, FTIR, and XRD characterization results are presented and chemical structures for the tetramer are proposed. The major components of the intermediate aggregates are likely highly symmetric phenazine- and dihydrophenazine-containing structures. These particular organic compounds have not been identified before as intermediates. The aggregation and precipitation of the tetramers apparently stabilizes these intermediates. The aggregates are highly crystalline, as evidenced by powder X-ray diffraction. A new reaction mechanism for the formation of these intermediates is proposed.
authors.affiliation: Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. zding@lanl.gov
authors.forename: Zhongfen
authors.initials: Z
authors.lastname: Ding
authors.forename: Timothy
authors.initials: T
authors.lastname: Sanchez
authors.forename: Andrea
authors.initials: A
authors.lastname: Labouriau
authors.forename: Srinivas
authors.initials: S
authors.lastname: Iyer
authors.forename: Toti
authors.initials: T
authors.lastname: Larson
authors.forename: Robert
authors.initials: R
authors.lastname: Currier
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Zhao
authors.forename: Dali
authors.initials: D
authors.lastname: Yang
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011108:Polymers / Q000737:chemistry*; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
chemical_list: D000814:Aniline Compounds; D011108:Polymers; D011522:Protons; C023650:aniline