AbstractThe radical cation nature of poly(p‐phenylene) (PPP) was examined by electron spin resonance (ESR) and chemical means. ESR studies revealed a radical concentration of 1.0 × 1021spins/g for the crude polymer. Workup with aqueous acid decreased the value to 1.5 × 1018spins/g. Reactions of the polymer with certain nucleophiles followed the half‐regeneration mechanism, whereas with others, electron transfer mainly occurred. The origin of halogen in the polymer was found to arise from reaction of the radical cation with the oxidant, and not with halide during workup. Oxidation of PPP with various species increased the concentration of radical ca