INFLUENCE OF THE DOPANT ON THE POLYPYRROLE MOISTURE-CONTENT - EFFECTSON CONDUCTIVITY AND THERMAL-STABILITY

Having in mind to produce electrically conductive carbon-epoxy composi te materials, we have filled an insulating epoxy resin with an electro nic conducting polymer, polypyrrole (PPy). To select the PPy that best suits this process, various PPys were chemically synthesized. The syn theses were performed in water via a dispersion polymerization route u sing, initially, either FeCl3 (PPy-Cl-) or (NH4)(2)S2O8 (PPy-HSO4-) as oxidizing agents. Then, using (NH4)(2)S2O8 as the oxidant, two other PPy doped with aromatic species were obtained due to the dissolution o f paratoluenesulfonic acid (PPy-TS-) or naphtalenesulfonic acid (PPy-N S-) in the reaction media. The characterization of the PPy samples by conductivity measurements, together with elemental and thermal analysi s, showed that PPy-TS- exhibits the highest conductivity and thermal s tability, with the conductivity remaining steady over 14 days. In addi tion, a stabilizing effect of the aromatic anions was observed. The ex periments have shown that moisture in the PPy cannot be entirely remov ed and that, with increasing moisture content, the conductivity also i ncreases, indicating an ionic conductivity superimposed on the electro nic conductivity usually observed in PPy. (C) 1998 John Wiley & Sons, Inc.