Pyrrole polymerization on polyimide surfaces creates conductive nano-domains

Oxidative polymerization of pyrrole on the surface of polyimide (PI) films was demonstrated to generate uniform, adherent coatings consisting of polypyrrole (PPy) electro-active nano-domains. This polymerization was carried out in aqueous methanol solution with FeCl3 as oxidant/dopant. Model kinetic reactions carried out by hydrogen Nuclear Magnetic Resonance (1H NMR) spectroscopy using ammonium persulfate (APS) as oxidant found evidence for an increase in the polymerization rate of pyrrole in the presence of a molar excess of PI. Attempts to identify changes to the PI chemical structure during pyrrole polymerization were investigated by high-resolution carbon 13C NMR spectroscopy and Infrared Attenuated Total Reflection (IR-ATR) spectroscopy. No differences were observed in concentrated D2SO4 solutions by NMR. However, IR-ATR noted a shift to lower wavenumbers of the PI carbonyl band and a higher wavenumber shift of the aromatic ether band. The morphology of PPy-coated PI films was analyzed by atomic force microscopy (AFM). The average size of PPy nanospheres was in the range of 20 nm with narrow distribution and was found to increase with reaction time.