Electropolymerization of methacrylonitrile and N-vinyl-2-pyrrolidone as probed by an EQCM

The electropolymerization of methacrylonitrile (MAN) and N-vinyl-2-pyrrolid one (NVP) in anhydrous acetonitrile has been followed in situ using an elec trochemical quartz crystal microbalance (EQCM). These two monomers essentia lly differ in that MAN leads to both a grafted polymer and a polymer formed in solution,while NVP only delivers the grafted polymer. For both molecule s, our results indicate that the frequency response of the EQCM anticipates the voltammetric response. In the case of MAN,the admittance of the EQCM s hows a considerable increase which is synchronized with the voltammetric pe ak. Alternatively, in the case of NVP, the admittance of the EQCM remains a lmost constant during the course of the experiment. These results lead us t o the proposal that: (i) the eigenfrequency variations of the EQCM may be r elated to mass changes on the surface of the quartz crystal in the case of the electropolymerization of NVP molecules over the whole potential range, while the same is true only over a few hundreds of mV before the peak in th e case of MAN; (ii) poly-NVP films grow directly from the surface of the el ectrode, while at least two regimes are detectable in the case of MAN. (C) 1999 Elsevier Science S.A. All rights reserved.