Spectroscopic, thermal and electrical properties of sulphonic acids doped poly(o-anisidine) and their application as humidity sensor

Poly(o-anisidine), P(o-anis) doped with camphor sulphonic acid (CSA) and p-toluene sulphonic acid (p-TSA) was synthesized by in situ chemical polymerization method using ammonium persulphate as an oxidizing agent. This is a single step polymerization process for the direct synthesis of emeraldine salt phase of the polymer. The polymers were characterized by using UV-vis and FT-IR spectroscopy, TGA and conductivity measurements. Formation of mixed phases of polymer together with conducting emeraldine salt phase are confirmed by spectroscopic techniques. Thermal analysis shows that poly(o-anisidine) has three stage decomposition pattern similar to unsubstituted polyaniline. The lower conductivity in poly(o-anisidine) compared to polyaniline is due to the cumulative steric as well as electronic effects of the bulky methoxy substituent present on the benzene ring. High temperature conductivity measurements show 'thermal activated behaviour'. The change in resistance with respect to % relative humidity (RH) is observed, when pressed pellets of the polymer were exposed to the broad range of humidity (ranging between 20-100% RH).