AN INSITU MULTIPLE INTERNAL-REFLECTION FOURIER-TRANSFORM INFRARED SPECTROSCOPIC (MIRFTIRS) INVESTIGATION OF THE GROWTH-MECHANISM OF POLYPHENYLENE DURING ELECTROOXIDATION OF BIPHENYL IN METHYLENE DICHLORIDE

The MIRFTIRS method has been applied to study in-situ the growth mechanism of polyphenylene films during electrooxidation of biphenyl in methylene dichloride on platinum. When the electrode is polarized at 1.5 V vs. Ag/AgCl, a band at 1600 cm-1 is observed, indicating a quinoid structure characteristic of the bipolaron state. The band disappears at potentials of 0 or -1 V. The polymer is in a neutral state but a residual concentration of NBu4BF4 salt remains in the film matrix. An important structural difference is observed between inner layers detected by MIRFTIRS (thickness from the electrode surface <1 μm) and outer layers of films analysed by ex-situ IR spectroscopy. The inner layers are formed by short and crosslinked chains, while the outer layers consist of longer and more linear chains. The solvent and residual water adsorb reversibly on the polymer, by Lewis acid-base interactions. When the polymer is in the oxidized state, the solvent of acidic character is removed from the polymer surface while adsorption of the more basic residual water is observed. The opposite is observed when the polymer is in the neutral state: the solvent enters again into the polymer and the adsorbed water is expelled from the surface. © 1990.