Oxidation and ion migration during synthesis and degradation of electroactive polymer–nylon 6 composite films

Abstract

In the synthesis of polyaniline–nylon 6 composite films wherein the polymerization was carried out by the immersion of aniline-containing nylon 6 films in an acid solution which has an oxidant ((NH4)2S2O8), the polymerization time has to be carefully monitored to prevent over-oxidation of the polyaniline. This method is likely to yield polyaniline in the protonated pernigraniline (rather than the emeraldine) state which undergoes hydrolysis in the acidic medium. Polyaniline–nylon 6 composite films with Cl− are converted to the base form as the counter-ions readily lose the Cl− anions when immersed in water. In contrast, the use of sulfosalicylic acid (SSA) as the protonic acid yields composite films which do not convert to the base form after extended exposure to water or under simulated weathering conditions. In the synthesis of polypyrrole–nylon 6 composite films, a substantial amount of polypyrrole can be readily formed in the nylon 6 matrix resulting in the destruction of the crystalline structure of the nylon 6 film and a large decrease in tensile strength. A significant amount of the iron chloride used as oxidant is also retained in the film causing blackening of the film under heating or simulated weathering. The removal of iron chloride from the film is not readily achieved by immersing the film in water but more so in SSA. The SSA anions also lend a greater degree of stability to the film upon exposure to water.