On the electropolymerization of methacrylonitrile and acrylonitrile as studied by CV, EQCM and EIS

The cathodic electropolymerization of acrylic monomers such as acrylonitrile (AN) and methacrylonitrile (MAN) gives two types of polymer. One is produced in the solution and the second is deposited as an adherent film on various metallic substrates. Whereas the mechanism of polymerization in solution is well known, the nature and the origin of the polymer bound to the electrode remains controversial. This controversy concerns the possibility of grafting a polymer onto a metallic electrode through an electrochemical reduction process. This paper is an attempt to reinterpret previous data in the light of more recent results obtained by double potential step chronoamperometry, the electrochemical quartz crystal microbalance (EQCM) and electrochemical impedance spectroscopy (EIS), which reveal more complex behavior than observed previously. At high monomer concentration a self-inhibition peak is obtained on the reduction current curve. This peak is attributed to a combination of two processes: formation of a monomer-depleted zone due to polymerization, which reduces the current, and precipitation of the polymer, which blocks the electrode. It is proposed here that the polymer is grafted onto the electrode by precipitation and reoxidation of non-terminated chain ends during the reverse scan.