Morphology and shape memory effect of segmented polyurethanes. Part І: With crystalline reversible phase

Abstract

A set of segment polyurethanes were synthesized and were proved to have interconnected, isolated and no hard-segmented domains. It was found that the shape fixity of the polyurethanes decreased with the increase of hard-segment content. The polyurethanes with hard-segment content from 30% to 50% had to be deformed at least to 100% strain to obtain good shape fixity. The segmented polyurethane having no hard-segment domains showed over 90% shape recovery under particular conditions. The segmented polyurethanes having interconnected hard-segment domains showed dramatically decreased shape recovery. The segmented polyurethanes having isolated hard-segment domains showed better shape recovery. When the polyurethanes were heated up to sufficiently high temperature they mostly recovered to their original shape. Stress relaxation would bring decrease to the shape recovery of the polyurethanes, especially to that of the segmented polyurethanes with low hard-segment content of 15% and 20%. For the segmented polyurethanes have isolated hard-segment domains the shape recovery decreased when the deformation amplitude increased from 50% to 200% and stopped decreasing as deformation amplitude increased to 250%. The shape recovery of the segmented polyurethanes could be enhanced nearly to 100% by a pre-deformation treatment.