Conducting Polyheterocycle Composites Based on Porous Hosts *

Conducting composites based on porous substrates (cotton fiber, non-woven polypropylene mat and porous crosslinked polystyrene) have been prepared by a two-step imbibition technique. First, the substrate was imbibed with a solution of monomer (pyrrole or bithiophene) in acetonitrile, followed by partial drying. Subsequently, the substrate was again imbibed, this time with an oxidant dissolved in a suitable solvent. The polymerization of the monomer inside the host in the presence of the oxidant and the doping of the polymer with the oxidant leads to the conducting composite. The highly hydrophobic and porous crosslinked polystyrene, prepared by the concentrated emulsion polymerization method, is the most efficient. The solvent employed for the oxidant plays a major role. A FeCl₃-methanol system and porous crosslinked polystyrene lead to conductivities of polythiophene- and polypyrrole-based composites of 3.63 and 0.65 S/cm, respectively. Copper perchlorate and iron perchlorate are also suitable oxidants. The environmental and thermal stabilities of polypyrrole-based composites are lower than those of polythiophene-based composites. The thermal stability of polypyrrole-based composites can be enhanced by including a small amount of an organic antioxidant, such as amides or substituted phenols, in the composites.