Thermal stability of electrochemically synthesized polypyrrole

Polypyrrole (PPy) films synthesized electrochemically with various dopants were investigated in terms of thermal stability and electrical conductivity at high temperatures. The conductivity of PPy films ranged from 4 S/cm to 130 S/cm depending greatly on the kinds of dopants used. A considerable weight loss was observed in a temperature range of 200∼400°C on thermogravimetric analysis (TGA). PPy doped with a thermally stable dopant such as anthraquinone-2-sulfonate ion lost its weight slightly at 250°C on TGA but the conductivity changed little on isothermal heating at 200°C as well as at 250°C. But a PPy film doped with a thermally less stable dopant showed a large decay in the conductivity as well as the weight loss on heating at 200°C. In the case of thermally unstable samples, a blue shift of the absorption band at 480 nm was observed possibly due to a reduction in π-conjugation length on the thermal degradation of the polymers or the dopants.