Shape memory polyurethanes phase separation

Phase separation of T-type high performance shape memory polyurethane... 

SS) and the hard phase e (HS). The shape fixing and shape recovery are strongly related to (SS) and (HS). The distribution of viscoelastic deformation between soft and hard phases is dependent on the two-phase morphology such as phase separation, phase composition, domain sizes, domain concentration and coimectivity, etc. Thus the shape memory properties ate defined by the two-phase morphological stmcture of the segmented polyurethanes. 

In this paper, we present results on shape memory behavior of polyurethane (PU)/clay nanocomposites. These nanocomposites were prepared via bulk polymerization method and contained exfoliated clay particles as revealed by transmission electron microscopy and wide angle X-ray diffraction method. The PU matrix contained a crystalline soft segment, which was responsible for shape fixity. The presence of clay decreased the crystallinity of soft segments and consequently shape fixity, but the magnitude of shape recovery stress increased, e.g., by 20% with only 1 wt% clay. The mechanism of reinforcement was studied by monitoring stress relaxation and phase separation. 

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