Photolysis of bisphenol-based polyurethanes, using bisphenols A, S, and AF with methylene diphenyl diisocyanate (MDI), has been shown by the observed changes in fluorescence spectra, reduced viscosity, and UV absorbance. Analysis of the fluorescence spectra of model compounds and polymers showed that para-photo-Fries and cleavage-type products were the major components formed during photolysis. The reduced viscosity and UV absorbance changes are consistent with a two-step photodegradation process. The reduced viscosity changes indicate that oxygen inhibition on the cleavage process is more significant for bisphenol S-based polyurethanes than for bisphenol A- and bisphenol AF-based polyurethanes.
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Liaw et al. (1999) studied this question.
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