FORMATION OF POLYPARAPHENYLENE (PPP) FILMS BY ELECTROOXIDATION OF BIPHENYL IN CH2CL2 - A STUDY OF THE NUCLEATION PROCESS AT A PLATINUM-ELECTRODE

The nucleation of polyparaphenylene (PPP) was investigated at a Pt electrode by oxidation of biphenyl in a solution of tetrabutylammonium tetrafluoroborate (TBABF4) in methylene dichloride (CH2Cl2). The chronoamperometric plots were characterized by a (I0, t0) minimum related to the applied potential by the relationship ln t0 = k0E + C1. For t << t0 (zone I), the current is due mainly to the charging of the electrode. For t > t0 (the charging current is negligible), and for t values very close to t0 (zone IIa) a linear relationship (I - I0)2/3 = at + b was observed. This was shown to be related to a progressive nucleation of small hemispherical crystallites of which the kinetics were controlled by spherical diffusion. For higher t values (zone IIb), and contrary to zone IIa, a sharp decrease of I was observed when the electrode was rotated, indicating in this case that radical cations diffuse towards the bulk of the solution and do not react to form the polymer. Microscopic observation of the surface at a time corresponding to zone IIa confirmed the presence of nuclei whose radii were shown to increase with time.