Highly Conductive and Thermally Stable Self-doping Propylthiosulfonated Polyanilines

A new type of highly conductive self-doping polyaniline, MPS−Pan, containing a sulfonic acid moiety covalently bonded to the polymer backbone through an electron-donating propylthio linkage has been successfully prepared via a novel concurrent reduction and substitution route. At a similar self-doping level, the resultant MPS−Pans displayed much higher conductivity than the corresponding sulfonated polyaniline (S−Pan). Furthermore, for fully doped samples, contrary to the trend of decreasing conductivity with the sulfonation degree in S−Pan, the conductivity of MPS−Pan was found to increase with its substitution degree. These results agreed with the expectation that electron-deficient charge carriers (e.g. semiquinone radical cations) on acid-doped polyaniline chains will be better stabilized by the electron-donating alkylthio substituent. Surprisingly, TG and XPS studies showed that MPS−Pan was thermally much more stable than S−Pan, with S−Pan starting to lose its sulfonic acid dopant at 185 °C, while MPS−Pan remained intact up to ∼260 °C.