Synthesis of polypyrrole and its derivative nanoparticles via a surfactant-free coupling polymerization protocol

Surfactant-free coupling polymerization of pyrrole (Py) and its derivatives, namely, N-methylpyrrole (MPy) and N-ethylpyrrole (EPy), was conducted using solid Fe(NO₃)₃ in the presence of an aqueous medium, resulting in aqueous dispersions of polymer particles. Dynamic light scattering studies revealed the production of colloidally stable polymer nanoparticles with diameters of 153–206 nm, 262–294 nm and 273–278 nm in aqueous media for the Py, MPy and EPy systems, respectively. The particle sizes of poly(N-methylpyrrole) (PMPy) and poly(N-ethylpyrrole) (PEPy) were larger than those of polypyrrole (PPy), which could be due to the greater hydrophobicity of MPy and EPy than Py. The particles could achieve colloidal stability through an electrostatic stabilization mechanism, as the polymerization process introduces cationic charges to the polymers via doping. Larger amounts of hydroxy and carbonyl groups were introduced into PMPy and PEPy because of the easier overoxidation of MPy and EPy due to their lower redox potentials than that of Py. Furthermore, the resulting particles could adsorb on oil‒water interfaces and work as effective Pickering-type emulsifiers. Suspension polymerization of vinyl monomer-in-water Pickering emulsions stabilized with PPy and PMPy nanoparticles resulted in the production of nanoparticle-coated polymer microparticles with diameters of 25 μm and 154 μm, respectively.