Raman spectroscopic studies on the structural changes of electrosynthesized polypyrrole films during heating and cooling processes

Polypyrrole films were electrochemically synthesized by direct oxidative polymerization of pyrrole in acetonitrile containing beta-naphthalene sulfonic acid or tetrabutylammonium tetrafluoroborate as an supporting electrolyte. We characterized the as-grown polypyrrole films by resonance Raman spectroscopy in the temperature region of -195 to 275degreesC. During the heating process, the Raman bands related to the oxidized species decreased gradually, due mainly to the affect of oxygen and moisture in the air, and, finally, the neutral polymer chains decomposed into disordered carbons. During the cooling process, polymer chains changed from disordered (coil-like) to ordered (rodlike) structures and caused the elongation of the conjugated chain length. This results in a red shift of the absorption of the electron spectra of the polymer and the enhancements of the Raman bands related to the oxidized species. (C) 2003 Wiley Periodicals, Inc.