FTIR Analysis of Chemical Gradients in Thermally Processed Molded Polyurethane Foam

Thermally processed PU foams are examined as a function of processing temperatures (25, 45, 65, and 85°C) at the side, middle, and center of a simple cylindrical mold. The PU foams show both chemical and morphological differences as a function of the processing temperature and radial position within the mold. Thermal degradation of uretoneimine structures, the emergence of carbodiimide structures, and extent of reaction of isocyanate groups are measured using photoacoustic FTIR spectroscopy. Chemical gradients and morphology differences between the side, middle, and center of the molded foam are observed for all processing temperatures. The data indicate that thermal activation at the center of the mold is important for samples regardless of processing temperature. Furthermore, in spite of thermal processing at temperatures well above the decomposition of uretoneimine structures (40°C), chemical gradients remain within the simple molded foams.