ABSTRACT:The main scope of this article was to demonstrate the potential of Fourier transform infrared (FTIR) spectroscopy as a diagnostic tool for low-pressure plasma polymer modification. Two model polymers, polyethylene and polystyrene, were treated in radio-frequency (rf) discharges in argon, hydrogen, oxygen, nitrogen, and tetrafluoromethane. In situ FTIR analysis was based on infrared reflection absorption spectroscopy (IRRAS) and attenuated total reflection (ATR). For both techniques, thin-film samples were prepared from polymer solution. The effects appearing in the infrared spectra are discussed. The results are compared with those from other diagnostic techniques.