DYNAMIC-MECHANICAL THERMAL AND INFRARED ANALYSES OF POLYACRYLONITRILEELECTROGRAFTED ONTO A METAL

Polyacrylonitrile (PAN) films have been ''grafted'' onto copper electr odes by cathodic polarization and analyzed by infrared spectroscopy an d dynamic mechanical thermal analysis (DMTA). The dynamic mechanical r esponse shows two or three transitions depending on the film thickness and the potential deposition. The viscoelastic properties of ''ungraf ted'' PAN films, e.g., solvent cast films of commercially available PA N, are deeply different from those of ''electrografted'' films. The ex perimental data support that ''ungrafted'' chains are paracrystalline in contrast to the ''grafted'' ones which are essentially amorphous. M oreover, the irreversible transformation of the ''grafted'' PAN chains observed beyond 225 degrees C is con firmed by Fourier transform infr ared (FTIR) analysis and ascribed to an intramolecular cyclization of PAN into polyimine. This reaction occurs rapidly and at a comparativel y low temperature with respect to ''ungrafted'' PAN, which suggests th at the ''grafted'' chain configuration might be predominantly isotacti c. The isotacticity and the amorphous structure appear to decrease as the thickness of the PAN film is increased. Literature data and the he rein reported observations would suggest a dependence of the amorphous structure of PAN on the chain isotacticity. (C) 1998 John Wiley & Son s, Inc.