Two‐Way Shape Changes of a Shape‐Memory Poly(ester urethane)

Phase‐segregated PEU exhibits two‐way shape changes under various constant stresses. Most distinct actuation (expansion on cooling and contraction on heating) can be detected between +60 and −20 °C when the maximum stress applied during a thermo‐mechanical pretreatment approached the point where deformation‐induced crystallization of the PBA soft segment sets in. The driving forces for the strain‐related two‐way shape changes consist of PBA crystallization and PBA melting‐induced entropy elasticity. At low constant stresses (<1.5 MPa), entropy elasticity also contributes to specimen expansion on cooling. The results of multiple‐ cycling experiments imply that PEU is an appropriate candidate for the fabrication of thermoresponsive actuators working under constant stress conditions.