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Microphase separation is investigated for segmented polyurethane copolymers synthesized from 4,4‘-methylenediphenyl diisocyanate and 1,4-butanediol as the hard segments and poly(hexamethylene oxide diol) and hydroxyl-terminated polydimethylsiloxane as soft segments. The neat PDMS-based diol exhibits two segmental relaxations corresponding to the principal repeating unit, Si(CH 3 ) 2 O, and to the hydroxyl end-group segments. When incorporated in the polyurethanes, the siloxane units form their own phase, while the end-group segments are mixed with the second macrodiol and some short hard segment sequences. This is demonstrated by the results of dynamic mechanical analysis and wide-angle X-ray diffraction experiments. The microdomain morphology was characterized principally by small-angle X-ray scattering, and the scattering data were analyzed with a pseudo-two-phase model as well as a modified three-phase core−shell model.
Hernández et al. (Fri,) studied this question.