Poly(N-methylaniline) microsphere formation and control of the average diameter by simple chemical polymerization

Microspheres of conducting poly(N-methylaniline) (PNMA) were successfully synthesized in aqueous solutions through chemical polymerization using only N-methylaniline as monomer, acid and oxidant without any templates. The microspheres were obtained only from acid solutions containing highly lyophilic anions such as ClO4−, BF4− and adipate ions. Several oxidants were employed and (NH4)2S2O8 was found to be the most appropriate for the microsphere formation. The average diameter of the microspheres with smooth surfaces was 0.38 μm when 25 mM N-methylaniline was oxidized with 25 mM (NH4)2S2O8 in 25 mM adipic acid solution at 25 °C. Although the average diameter was barely influenced by the acid concentration of the polymerizing solution, it could be controlled by three parameters: monomer concentration, reaction time and temperature. It was found further that the acid concentration is critical for the formation of the microspheres with smooth surfaces. The smooth surfaces were observed only when the acid concentration was less than 50 mM.