Photochemical reactions in an MDI-based elastomeric polyurethane

Polyurethanes based on diphenylmethane 4,4′-diisocyanate (MDI) were examined by electronic spectroscopy and by continuous and laser flash photolysis. Fluorescence and phosphorescence emissions were observed, and although the source of the fluorescence could not be identified, the phosphorescence appears to originate from a benzophenone-type oxidation impurity. On laser flash photolysis, transient absorptions were observed at 375 nm and 580 nm. The latter is assigned to a ketyl radical center formed by hydrogen abstraction from the polymer matrix. Participation of these species in the photochemical reactions leading to deterioration of the MDI-based polyurethane is discussed.