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 electropolymer ization of benzene or biphenyl in different electrolytic media. it is shown that crosslinked polyphenylenes with a low degree of polymerizat ion (DP similar to 10) are obtained in organic media with fluorinated salts. The growth of the polymer in organic media, shown to be control led by the progressive nucleation of hemispherical nuclei and a spheri cal monomer diffusion step, is inhibited by traces of water. This inhi bition is explained by considering a heterogeneous adsorption equilibr ium between water and the poly(para-phenylene) (PPP) nuclei, and deact ivation 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 aci dic media, particularly triflic acid in liquid SO2 or in acidic organi c solvents. In this case, extremely linear and well-organized PPP chai ns with DP higher than 30 are obtained, leading to cyclic voltammogram s with very sharp, well-separated redox peaks, related to a strong int eraction of CF3SO2H with benzene or biphenyl. The nature of the solven t used for the synthesis of PPP films significantly affects their micr ostructure: 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 pe aks, related to the fact that the interactions between PPP chains and CF3SO3H are weaker in CH3NO2 than in the more acidic CH2Cl2 or SO2.