Thermal behavior of doped polyaniline

Abstract

Summary form only given. Thermal stability in air of polyaniline (PAn) doped with different dopant has been investigated by TG, DSC and in-situ electrical conductivity measurements. The onset temperature of apparent dopant evolution (Tc) for doped-PAn varies greatly from dopant to dopant. H/sub 2/SO/sub 4/- doped PAn is still stable at 190/spl deg/C whereas HCl evolves at 150/spl deg/C for the HCl-doped PAn. Electrical conductivity of sulfonated polyaniline keeps unchanged after it is treated at 200/spl deg/C for 2hr, but decreases 3-4 orders of magnitude after it is treated at 220/spl deg/C for 3hr. Thermal stability of PAn doped with organic acid such as (p-toluene sulfonic acid (TSA) , naphthalene 1,5-disulfonic acid or 5-sulphosaIicylic acid) is better than that doped with inorganic acids. The electrical conductivity of TSA-doped PAn decreases 4 orders of magnitude after it is treated at 230/spl deg/C for 2hr, but the IR and elemental analysis indicate that there is no dopant evolution during thermal treatment. The serious thermal oxidative cross-linking between PAn molecular chains at 220-250/spl deg/C is responsible for the decrease in electrical conductivity. Thermal stability of PAn doped with macromolecular acid (sulfonated polystyrene and sulfonated poly-p-phenylene oxide) is better than that of low molecular acid doped PAn.