STABILITY OF CHEMICALLY SYNTHESIZED POLYPYRROLE FILMS

Polypyrrole powders and films deposited on various fabrics are chemically synthesized by reaction of FeCl3 with pyrrole in an aqueous solution containing an optional sulfonate dopant (p-toluenesulfonate or 2-naphthalenesulfonate). Two synthesis processes are used and the resulting materials are compared. Electrical conductivities are measured, doping levels are determined by neutronic activation and dedoping phenomena are appreciated by evolved-gas analysis. Ageing experiments in ambient air at various temperatures are performed and conductivity decays are measured in situ for kinetic studies. These materials present good conductivities (120 S/cm) or area resistivities (5 OMEGA/square) due to the preferential incorporation of the sulfonate in the polymer. Our best films exhibit higher stability than electrochemical samples (evaluated t1/2 = 2800 days at ambient temperature) in relation with a high thermal activation of the conductivity decay (E(a) = 20 kcal/mol). The conductivity decay of these films appears to follow a diffusion-controlled kinetics. This diffusion phenomenon appears to be solid state diffusion (D = 10(-18)-10(-17) cm2/s). Polypyrroles doped with 2-naphthalenesulfonate are found to be more stable than samples doped with the usual p-toluenesulfonate.