Catalytic Polymerization of Aniline and Its Derivatives by Using Copper(II) Salts and Oxygen. New Type of Polyaniline with Branched Structure

The catalytic polymerization of aniline and its derivatives was performed by stirring the solution of the corresponding monomer and copper(II) salts (50/5, mmol/mmol) in acetonitrile and water (1/1, v/v) under oxygen at room temperature for 24 h. Among copper salts, CuBr2 and CuCl2 are more active than the others. In each case the copper salts do not work as a stoichiometrical oxidant but work as a catalyst, which can be proved on the basis of turn-over-frequency. The polymers isolated were characteristic of polyaniline with an Emeraldine structure, although a small amount of branched structures were by-produced by an addition reaction at ortho-position. Thus, heat treatment of the polymer at 284 °C results in partial decomposition to produce the stable polymer and aniline. Although the resulting polymer had an Emeraldine type structure, a strong doping effect on its electroconductivity was not observed, probably because of the amorphous morphology. The UV-vis spectra of the reaction solution have suggested that the catalytic polymerization of aniline proceeds through the formation of the copper(II) complex of aniline.