Fluorescence and IR Characterization of Cure in Polyurea, Polyurethane, and Polyurethane−Urea

Abstract

Fluorescence and IR spectroscopic techniques have been used to characterize cure in polyurea (PUa), polyurethane (PU), and polyurethane−urea (PUU), based on the study of model compounds. Polyurea cured in a nonreactive diluent by reacting liquid MDI (4,4‘-methylenebisphenyl diisocyanate) with 3,5-diethyltoluene diamine (DETDA) showed fluorescence intensity decrease at 339 nm due to DETDA consumption and an emerging peak near 310 nm from the formation of the urea derivative of MDI. The reaction at room temperature was complete after 50 min with supporting IR evidence of urea carbonyl at 1642 cm-1. When nonfluorescent liquid MDI was reacted with ethylene oxide terminated PPO (EO−PPO) to form polyurethane, the fluorescence intensity at 310 nm increased slowly, taking approximately 1500 min to plateau with an intensity increase of at least 15 times. For PUU, which was cured by reacting MDI, EO−PPO, and DETDA, the fluorescence behavior was more complex: first, a peak at 303 nm showed up immediately following the mixing of the reactants, probably due to urea group formation, while the peak at 333 nm decreased due to DETDA consumption, and second, the peak intensity at 303 nm, after a slight decrease began to increase with a gradual shift to 310 nm. These results were correlated with the overall extent of cure as well as the extent of urea and urethane formation monitored by FTIR spectroscopy. Within certain regions, the fluorescence behavior can be correlated to the extent of urea and urethane reaction.