Aniline and its ring-substituted derivatives are oxidatively polymerized by H 2 O 2 to the corresponding electrically conductive emeraldine oxidation state in dilute aqueous acids when 5 M CaCl 2 is added as an ionic strength booster. Evidence consistent with the intermediacy of HOCl as the primary oxidant is presented, which is formed in situ in this system. This study significantly advances the scope of our previous report on aniline polymerization using the H 2 O 2 /NaCl/HCl oxidant system. For example, the H 2 O 2 /CaCl 2 /HCl oxidant system significantly increases the reaction yield and polymer molecular weight and affords entry into a wide range of polyaniline derivatives with technologically interesting nanostructure. Aniline and its derivatives are very sparingly soluble in 5 M CaCl 2 with chain growth occurring almost entirely in the solid state. This opens new opportunities to control the morphology of polyaniline by carefully controlling the corresponding morphology of the freshly precipitated monomer salt.

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