ESR susceptibility and conductivity on polypyrrole: effect of ageing

Summary form only given. For technical applications, one of the most important requirements of conducting polymers is the stability of conductivity. The correlation between conductivity and spin susceptibility in these materials has been the subject of a number of studies. In the present work we report ESR experiments on aged polypyrrole samples. Polypyrrole powder was obtained by chemical oxidation at 3/spl deg/C with 1-naphthalen sulfonic acid as doping species and then heated to 140/spl deg/C either under air or argon to accelerate the ageing process. Quantitative measurements have been carried out as a function of heating time. In the case of fresh chemical powder we observe a broad ESR line (/spl sim/200 Gauss) which decreases with heating time to a few gauss while the spin susceptibility remains constant. ESR data are discussed and compared to those of conductivity measurements obtained in the same conditions.