Structural changes associated with thermal and chemical treatment of polythiophenes doped with perchlorate

Abstract

Electrically conductive polymers have been synthesized by the reaction of 3-methylthiophene or 2,2′-bithiophene with ferric perchlorate. With copper perchlorate, only 2,2′-bithiophene undergoes simultaneous polymerization and oxidation. Neither ferric perchlorate nor copper perchlorate reacts with thiophene to yield a conducting polymer. X-ray photoelectron spectroscopy of the perchlorate doped polythiophenes indicates that, depending on the perchlorate used, a significant amount of the chlorine may be covalently bonded to the polymer. Treatment of the doped samples with methanol results in the ClO 4 − S ratio decreasing to one-third of the pristine value. Treatment with NaOH results in almost complete removal of the ClO 4 − anions in poly(bithiophene) synthesized with Fe(ClO 4) 3. 9H 2O. Concurrent with the loss of ClO 4 − anions is the decrease in electrical conductivity. The undoped polymer has a high degree of thermal stability while the decomposition of the doped polymer appears to be initiated by the decomposition of the ClO 4 − anions. Prolonged heating of the doped samples at 150°C results in the conversion of ClO 4 − anions to Cl covalently bonded to the polymer and to volatile species which are lost from the polymer.