Electron paramagnetic resonance investigation of free radicals in polyimide films

Both unirradiated and far-ultraviolet irradiated Kapton H polyimide films have been investigated by electron paramagnetic resonance spectroscopy as a function of temperature, microwave power, irradiation time, and chemical treatment. Free radicals are always observed in the bulk. Irradiation of Kapton H films in air produces relatively stable oxidized and unoxidized aromatic-type radicals in close vicinity of the surface, whereas film irradiation in the absence of oxygen yields only the latter radicals. The g values, line widths, spin concentrations, and relaxation times of both the bulk radicals in unirradiated films and the surface radicals in films irradiated in air have been determined. It was found that irradiation of Kapton H enhanced the adhesion of gold films to the polyimide surface. On the basis of the results of this study, a qualitative model for the radical-formation mechanism is proposed.