Depth profiling of photooxidized styrene-isoprene copolymers by photoacoustic and micro-Fourier transform infrared spectroscopy

Transmission micro-FT-IR (Fourier transform infrared) and photoacoustic (PA S) FT-IR analysis have been combined to determine the oxidation profiles of various photooxidized polyisoprene-polystyrene copolymers. It is shown tha t only the polyisoprene phase is oxidized. The front photooxidized layers ( 0-22 mu m) are analyzed by PAS, while the bulk (11-150 mu m) is characteriz ed by cross-sectional analysis of microtomed layers. A good agreement betwe en the two methods is found in the region where the analyzed layers overlap (11-22 mu m). The extent of the oxidation was determined by monitoring the ratio between the intensity of the carbonyl absorbance at 1718 cm(-1) and the absorbance at 1600 cm(-1). The results given in this article show that PAS FT-IR can be a rapid and nondestructive technique of quantitative chara cterization of the surface degradation of aged polymers.