Vibrational Spectra and Structure of Polyaniline

Vibrational spectra have been studied on polyaniline in various forms with different electrical properties: two conducting forms, as-polymerized (2S) and doped 1A polyanilines; and three insulating forms, reduced-alkali-treated (1A), acid-treated 1A (IS), and oxygen-treated 1A [1A(O₂)] polyanilines. Polyaniline 1A is spectroscopically evidenced to be poly(imino-l,4-phenylene), -(NHC₆H₄)_n-. Polyaniline 1S consists of imino-l,4-phenylene (IP) unit (-NHC₆H₄-) and its salt unit (-NH₂ ⁺A^--C₆H₄-, (A^-, anion)). Treatment of 1A with oxygen converts part of consecutive IP units (-NHC₆H₄NHC₆H₄-) to nitrilo-2,5-cyclo-hexadiene-l,4-diylidenenitrilo-l,4-phenylene (NP) unit (-N=C₆H₄=NC₆H₄-). Semiquinone radical cations of IP units exist only in the conducting forms of polyaniline, 2S and doped 1A, indicating that semiquinone radical cations play an important role in electrical conduction in polyaniline.