THERMAL-STABILITY OF POLYPYRROLES

The effect of dopants and level of doping on the thermal stability of polypyrrole at 90, 120 and 150-degrees-C in dry air and nitrogen was investigated by monitoring the decay of conductivity. Polymers doped with aromatic anions (p-toluene sulphonate and p-chlorobenzene sulphonate) exhibit better stability than polymers doped with an aliphatic anion (dodecyl sulphate). The conductivity decay appears to follow diffusion controlled kinetics. After an initial decrease in conductivity, polypyrrole doped with p-toluene sulphonate anion maintains a constant conductivity at 150-degrees-C in air for at least 4 weeks. Dedoping results in materials of lower conductivity but greater thermal stability Differential scanning calorimetry (DSC) and thermogravimetry (TG) were found to be useful techniques to characterize and investigate thermal stability. Oxidation of polypyrrole films, monitored by DSC, shows diffusion controlled kinetics. Although both oxidation and conductivity decay show typical diffusion kinetics, oxidation is a necessary but not sufficient condition for the decay.