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Photolysis of Segmented Polyurethanes. The Role of Hard-Segment Content and Hydrogen Bonding.
UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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The photodegradation of segmented polyurethanes based on methylene 4,4 -diphenyl diisocyanate MDI is shown to be dependent on the physical structure of the polymer. As the hard segment content of the polyurethane is increased, the photodegradation efficiency is lowered. In particular, the extent of the photolytic decomposition is inversely dependent on the degree of hydrogen bonding in the aryl carbamate groups in the polyurethane backbone. Utilizing appropriate model compounds for comparison, the formation of the ortho photo-Fries rearrangement product, as detected by fluorescence spectroscopy, is also shown to be dependent on the degree of hydrogen bonding. In general, the restrictive mobility imposed by hydrogen bonding is a critical factor which must be considered in the photochemistry of segmented polyurethanes.
APPROVED FOR PUBLIC RELEASE