Doped polyaniline materials with metal oxalate complexes of Cr, Fe, Mn, Co and Al were synthesized by in situ chemical oxidative polymerization of aniline using potassium perdisulphate as oxidant in aqueous sulphuric acid medium. These polymer materials were characterized by chemical analyses, spectral studies (UV-visible and IR), X-ray diffraction and thermal techniques and also by conductivity measurements by four-probe technique. The presence of complex anion in polyaniline material was confirmed by chemical and spectral analyses. The yield and conductivity of metal oxalate doped polyanilines were found to be high when compared to the simple sulphate ion doped polyaniline prepared under similar condition. UV-visible and IR spectral features not only confirmed the polyaniline doping by complex anions but also substantiated their facilitating effect on conductivity. The X-ray diffraction patterns indicated some crystalline nature in metal oxalate doped polyaniline and amorphous in polyaniline sulphate salt. The conductivity of the polymer samples strongly depended on the degree of crystallinity induced by complex counter anions as dopant. All the polymer materials, as evident from TGA curves, were observed to undergo three-step degradation of water loss, de-doping and decomposition of polymer. Further, the thermal stability of polyaniline was found to improve on doping with metal oxalate complex.

Polyaniline (Pani) and its metal oxalate composites (∼ 10 wt.%) of trivalent metal ions of Cr, Fe, Mn, Co and Al were synthesized by chemical oxidative polymerization technique with potassium perdisulphate oxidant in aqueous sulphuric acid medium. These materials were characterized by UV–VIS and EPR spectral techniques. Their d.c. electrical conductivities at room temperature and also as a function of temperature (307–453 K) were measured by four-probe technique. Presence of radical cation/polaron transition was indicated by UV–VIS absorption peak and EPR signals. Further, a close correlation existed between the conductivities and EPR parameters such as line width and peak ratio, which demonstrated that both mobile and fixed spins are involved in these composites. The dependence of conductivity on temperature, when analysed graphically by VRH, GB and TC mechanisms, pointed out that VRH is the predominant charge transport mechanism in these materials.