A STUDY OF THE STRUCTURE AND MORPHOLOGY OF POLY(P-PHENYLENE) FILMS ELECTROSYNTHESIZED IN LIQUID SO2 WITH DIFFERENT SALTS AT LOW-TEMPERATURES

The structure and electrochemical properties of poly(p-phenylene) (PPP ) films synthesized by oxidation of benzene in SO2 were investigated b y IR, UV, scanning electron microscopy and X-ray diffraction. In the p resence of a Lewis acid (SbF5) or boron trifluoride etherate complex ( (C2H5)(2)OBF3), the potential of benzene oxidation is shifted to low v alues and the lowest potentials are obtained when the interaction betw een benzene and the acid (pi-complex) is the strongest (1.6 and 1.1 V with (C2H5)(2)OBF3 and SbF5, respectively). As a general rule, the por osity of the PPP films decreases with temperature of synthesis, and th eir morphology depends on the synthesis conditions. They are amorphous with LiAsF6, but crystalline with other salts such as TBAX (X=BF4-, S bF6-), with SbF5 or(C2H5)(2)OBF3. A hexagonal structure (a=11.5 Angstr om, c=4.2 Angstrom) is found with TBABF(4) (crystallite size around 15 0 and 200 Angstrom), and an orthorhombic system with TBASbF(6) (a=16.5 0 Angstrom, b=13 Angstrom, c=4.12 Angstrom) or with SbF5 (a=15.03 Angs trom, b=11.25 Angstrom, c=4.2 Angstrom). The surface of the films is q uite smooth in the presence of (C2H5)(2)OBF3 or LiAsF6 and very rough with ammonium salts and SbF5. The homogeneity of the films, which is a volume property, is very good with films formed with LiAsF6 or SbF5 a t -75 degrees C and is evidenced by n-doping in THF+TBABF(4), which le ads to a uniform blue colour on the whole surface. On the contrary, th e homogeneity of films formed with (C2H5)(2)OBF3 is poor, and attested by the appearance of scattered blue stains by n-doping.