Shape-memory behavior of segmented polyurethanes with an amorphous reversible phase: The effect of block length and content

Segmented thermoplastic polyurethanes (TPU)s with amorphous soft segments f rom the reaction of hexamethylene diisocyanate and 1,2-butanediol and cryst alline hard segments from 4,4'-methylenediphenyl diisocyanate and 1,6-hexan ediol showed sharp glass-transition temperatures that could be used as shap e-recovery temperatures. The thermal, mechanical, and shape-memory effect o f these TPUs of various block compositions and lengths were studied by diff erential scanning calorimetry, dynamic mechanical testing, and tensile test ing. As the block, lengths decreased, phase mixing increased and hysteresis in the shape-memory behavior decreased. Too low a content of hard segments increased the hysteresis in the shape-memory behavior. (C) 2000 John Wiley & Sons, Inc.