STABILITY STUDIES OF THE ELECTRICAL-CONDUCTIVITY OF VARIOUS POLY(3-ALKYLTHIOPHENES)

The stability of the electrical conductivity of poly(3-alkylthiophenes) (P3ATs) was examined under systematically controlled environmental and thermal conditions. It was found that the stability of the alkyl-substituted polythiophenes increases as the length of the alkyl sidegroup decreases. The stability of the polymer conductivity can also be dramatically influenced by the nature of the counterion introduced into the polymer during doping, and to a lesser extent by the type of polymerization method used to prepare the polymer. P3ATs doped with FeCl3 were found to be considerably more stable than those doped with NOPF6 in part because of a thermally activated additional doping process that takes place in the FeCl3-doped samples at elevated temperatures and the lower flexibility of the FeCl3-doped polymer chains. Polymers synthesized via a chemical polymerization route are in general slightly more stable than those prepared via an electrochemical route. As revealed by FT-IR, UV-Vis spectroscopy and DSC, a process involving thermal undoping of the doped P3ATs upon heating appears to be driven by a conformational change of the polymer backbone which regenerates the original neutral polymer. This suggests that P3ATs with improved stability may be obtained by restricting the mobility of the polymer chain via post-processing crosslinking of the sidegroups.