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ABSTRACT:X-Ray photoelectron spectroscopy (XPS) studied have been performed on conductive polypyrrole (PPY)-halogen complexes, such as PPY-I2, PPY-Br2, and PPY-Cl2 complexes, prepared by the simultaneous chemical polymerization and oxidation of pyrrole by the respective halogens. Substantial halogenation of the pyrrole ring was observed in the case of PPY -Cl2 and PPY-Br 2 complexes. In the case of PPY -Br 2 complex, the ratio of covalent to ionic bromide content can be effectively varied over a wide range by varying the bromine to monomer ratio used for polymerization. The increase in covalent bromide content causes a decrease in the electrical conductivity of the complex. The Nls spectra suggest the presence of positively charged nitrogen species and their possible contribution to the electrical conductivity of the complexes. The Cls spectra for all the complexes reveal that close to 1/3 of the carbon atoms may have been associated with structural disorder, as in the case of electrochemically prepared PPY s.KEY WORDS X-Ray Photoelectron Spectroscopy / Polypyrrole-Halogen Complexes / Chemical Synthesis / Structural Disorder / Electrical Conductivity / Electroactive polymers have attracted a great deal of attention during the past decade because of their unusual electrical/electronic properties. A survey of the literature 1 -3 reveals that most of the recent interest on conductive polyheterocycles, polypyrrole (PPY) in particular, are devoted to the materials obtained from electrochemical polymerization and oxidation. For example, most of the Electron Spectroscopy for Chemical Applications (ESCA) studies were centered on electrochemically prepared polypyrrole and related polyheterocycles. 4 -8 These ESCA studies provided information pertaining to the nature of interactions between polymeric cations and their counter anions, and the structural disorder in these polymers arising from these interactions. However, there are still certain discrepancies 4 · 6 between the results reported.Rather conductive PPY complexes have also EXPERIMENTAL Polymer SamplesThe polypyrrole samples used for this study consist of various polypyrrole-halogen complexes, such as PPY-1 2 , PPY-Br 2 , and PPYCl2 complexes. All samples were prepared via the simultaneous chemical polymerization and oxidation of pyrrole by the respective halogen acceptor according to the methods reported earlier. 12 · 13 The PPY-Br2 and PPY-Cl2 complexes were prepared .in acetonitrile while the PPY-1 2 complex was prepared in an aqueous medium. In the case of PPY-Br 2 complexes, and to a lesser extent the PPY-Cl 2 and PPY-12 complexes, the amount of acceptor incorporated in the final complexes can be effectively varied by varying the monomer to halogen ratio used for the polymerization process. The final physicochemical and electrical properties of the PPY complexes are strongly affected by the type of acceptor incorporated and the nature of the polymer-acceptor interactions. ESCA MeasurementsX-Ray photoelectron spectroscopy (XPS) measurements were made on pow...

ABSTRACT:X-Ray photoelectron spectroscopy (XPS) studies have been performed on polypyrrole-2,3-dichloro-5,6-dicyano-p-benzoquinone (PPY-DDQ) and polypyrrole-tetrachloroo-benzoquinone (PPY---chloranil) complexes prepared via the simultaneous chemical polymerization and oxidation of pyrrole by the respective acceptor. XPS data suggested that the charge transfer interactions in both complexes probably proceeded further than the pure formation of a molecular complex. The negative charges of both organic anions were mainly localized on the oxygen and the chlorine atoms and to some extent on the nitrogen of DDQ. More extensive charge transfer interaction and higher fraction of pyrrole nitrogen with positive charge were observed in the PPY-DDQ complex, which exhibited a substantially higher electrical conductivity than the corresponding PPY ---chloranil complex.KEY WORDS XPS / Polypyrrole / 2,3-Dichloro-5,6-dicyano-p-benzoquinone / Chloranil / Charge Transfer Interactions / Due to their relative physicochemical and electrical stability and well-characterized stoichiometry, highly conductive polyheterocycles, polypyrrole (PPY) in particular, have attracted a great deal of interest in recent years. 1 · 2 Most of the recent interest on conductive PPYs, however, are devoted to the materials obtained from electrochemical polymerization and oxidation. For example, most of the X-Ray photoelectron spectroscopy (XPS) studies were centered on electrochemically prepared .PPYs and related polyheterocycles.3-7 We reported recently on the XPS technique as a convenient tool for analysing the polymer-acceptor interactions in chemically synthesized PPY-halogen complexes. 8

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