Electrografting is an attractive technique with the potential for controlling the electrochemical conditions required for producing functionalized polymeric macrostructures of a predictable, well-defined composition and thickness. The aim of this study was to investigate the electrografting process for the prototype electron deficient vinylic monomer, acrylonitrile, with the purpose of extending the technique to other more functional monomers. The experimental preparation and set-up used here has evolved via a series of improvements to a technique used previously in these laboratories in line with those adopted by the laboratories at CEA, Saclay for the electrografting of PAN (polyacrylonitrile). Although the requirement for stringent conditions is similar, the simplicity of the current set-up contrasts markedly with previous workers. Various experimental parameters such as the composition of the electrolyte, electrode preparation, environment conditions and potentiostat control were explored to establish the optimum growing conditions.
The effects of changing these parameters were monitored electrochemically using cyclic voltammetry and also by evaluating the morphology and chemical structure of electrografted films using a combination of AFM, ellipsometry, FTIR, Raman and UVVIS spectroscopies. In establishing the fundamental features of the electrografting technique, the study has highlighted the limitations of cyclic voltammetry as the sole technique for controlling the electrografting process.
Based on the AFM and FTIR data, the PAN films produced in this study were comparable in quality to those reported by CEA, Saclay, and the University of Liege groups. Their electrografted nature was confirmed by their ability to withstand a peel test and their insolubility in DMF (N, N-dimethylformamide). The FTIR spectra provide convincing evidence that the previous assignment of the 1670 cm^-1 band to PAN structural transformations is incorrect and actually arises from DMF incorporated into the PAN films.
This study was the first to use Raman spectroscopy to investigate the electrografting of PAN films and revealed new, previously unreported Raman peaks at 1096, 1520 and 1580 cm^-1, which are attributed to the formation of a ladder type network of vertically stacked polymer chains connected by azine bridges. Promising results from the experimental trials using a series of vinyl monomer derivatives have revealed the potential of the nitrile moiety as a useful electrografting engine to introduce more reactive functional moieties ( protected by THP) into the polymeric macrostructure. However, further work is necessary to fully characterise the electropolymer and to investigate the in-plane and out-of-plane attachment after deprotection.