Stress-Free Two-Way Shape Memory Polymers with Dual-Crystalline Phase Based on Poly(Tetramethylene Ether Glycol) and Poly(ε-Caprolactone).

Two-way shape memory polymers (2W-SMPs) are a class of smart materials and can undergo spontaneously reversible deformation after specific stimuli. It is crucial to develop 2W-SMPs to achieve precise control of two-way shape memory behavior without external forces and reveal their structure-property relationships. In this study, dual-crystalline phase crosslinked polymer networks based on poly(tetramethylene ether glycol) (PTMEG) and poly(ε-caprolactone) (PCL) are fabricated via thiol-ene click reactions. The networks with two independent melting temperatures are gained by adjusting the ratio of the two segments and the two-way shape memory is enabled using the temperature difference between the two phases. The effects of network composition, pre-tensile strain, and actuation temperature on the two-way shape memory properties are investigated and the two-way shape memory mechanism of dual-crystalline phase polymers is further elucidated. Among the various compositions of networks, PTMEG8-PCL2 exhibits the optimal two-way shape memory properties, with the actuation strain of 24.25% and reversible strain of up to 10.35% at the actuation temperature and pre-stretch strain of 45 °C and 15%, respectively, which is potential for soft robotics applications. It is believed that this work guides the design of semicrystalline networks with two-way shape memory properties.