Effects of Blended Reversible Epoxy Domains on Structures and Properties of Self-Healing/Shape-Memory Thermoplastic Polyurethane

Few thermoplastic polyurethane (TPU) blending materials are reported to tune shape-memory capability, self-healing ability, and recyclability as well as mechanical property due to the different requirement of phase morphologies. This work focuses on how reversible epoxy domains affect the structures and properties of TPUs that contain disulfide bonds in main chains. The blended epoxy oligomers with dangling furan groups are miscible with the TPU. Self-healing efficiency can be improved by such miscible epoxy oligomers that are also beneficial for shape recovery but harmful for shape fixation. In the presence of bis(4-maleimidophenyl)methane (BMI), crosslinked epoxy domains phase separate from the TPU matrix to form microscale domains after the Diels-Alder (DA) reaction between furan groups and maleimide groups in BMI. Elastic modulus and tensile strength of TPU are greatly improved in comparison with pristine TPU and TPU/epoxy blends without BMI. The phase-separated domains deteriorate the self-healing, and the presence of phase-separated microdomains facilitates the shape fixation but deteriorates the shape recovery. This work is not only useful to further understand the relation between structures of polymer blends with intelligent features, but also offers a useful approach to adjust the properties and capabilities of TPU in a cost-effective manner.