Coating of uniform inorganic particles with polymers: III. Polypyrrole on different metal oxides

Five kinds of uniform metal oxide particles (α-Fe₂O₃, CeO₂, CuO, NiO, and SiO₂) were coated with polypyrrole by reacting the dispersed solids with pyrrole in a water/ethanol medium without the use of a soluble oxidant. When the process was carried out in air, all particles were coated with the polymer, although the thickness of the layer varied on different cores. In CuO dispersions, independent polypyrrole particles were produced in addition to coated spheres. While oxygen is the major oxidant that initiates the polymerization of pyrrole, some metal oxides may also affect the reaction both in terms of the amount and the composition of the shell. Thus, α-Fe₂O₃ and SiO₂ were found to be inactive in the polymerization, while CeCh and CuO react with the adsorbed pyrrole molecules through a reductive-dissolution process, in which the monomers are oxidized, causing a release of reduced metal ions.