NEW SEGMENTED POLYURETHANE UREAS BASED ON 4,4'-DICYCLOHEXYLMETHANE DIISOCYANATE AND ON VARIOUS SOFT SEGMENTS

Linear segmented polyurethane ureas were prepared from 4,4'-dicyclohex yl-methane diisocyanate (H12MDI), 4,4'-diamino-3,3'-dicyclohexyl metha ne (3DCM), and various hydrophilic and hydrophobic soft segments. Kine tic studies of the synthesis of the diisocyanate-terminated prepolymer s revealed that the use of too Little reactive polyols (that is, polyo xypropylene that bears secondary hydroxyls) could be rather tricky; th e noncatalyzed reaction is very slow, but the use of a catalyst soon t riggers the formation of side products, and the processing window cons equently becomes quite short. Microcalorimetric and dynamic mechanical measurements showed that all the materials were highly phase-segregat ed elastomers and displayed good mechanical properties up to high temp erature (typically 180 degrees C), provided that they had been postcur ed properly; in this respect, the dramatic effects of isolated (nonche mically linked) hard segments, as well as of too low postcuring temper atures, were demonstrated. Polyurethane ureas compare well with polyur eas, and their synthesis can be a good way to cope with the lack of we ll-adapted commercial diamino-terminated prepolymers. (C) 1998 John Wi ley & Sons, Inc.