Structure and growth mechanisms of polyphenylene films formed on platinum by anodic polymerization of benzene and biphenyl in various electrolytic media

Polyphenylene films are deposited on platinum by anodic electropolymerization of benzene or biphenyl in different electrolytic media. It is shown that crosslinked polyphenylenes with a low degree of polymerization (DP ∼ 10) are obtained in organic media with fluorinated salts. The growth of the polymer in organic media, shown to be controlled by the progressive nucleation of hemispherical nuclei and a spherical monomer diffusion step, is inhibited by traces of water. This inhibition is explained by considering a heterogeneous adsorption equilibrium between water and the poly(para-phenylene) (PPP) nuclei, and deactivation of the nuclei surface by adsorbed water. PPP films with linear chains and higher DP (about 30) are obtained in liquid SO2 and at low temperatures. Further improvements are obtained by using strongly acidic media, particularly triflic acid in liquid SO2 or in acidic organic solvents. In this case, extremely linear and well-organized PPP chains with DP higher than 30 are obtained, leading to cyclic voltammograms with very sharp, well-separated redox peaks, related to a strong interaction of CF3SO3H with benzene or biphenyl. The nature of the solvent used for the synthesis of PPP films significantly affects their microstructure: PPP films synthesized in CH2Cl2 (or SO2) + CF3SO3H exhibit sharp redox peaks when submitted to cyclic voltammetry in H2SO4 (95%), whereas PPP films obtained in CH3NO2 + CF3SO3H give broader redox peaks, related to the fact that the interactions between PPP chains and CF3SO3H are weaker in CH3NO2 than in the more acidic CH2Cl2 or SO2.