Capturing Robust and Tough Thermoplastic Polyurethane Elastomers via Engineering Dual-Phase Evolution Rather than Chain Extenders

Strengthening and toughening thermoplastic polyurethane (TPU) elastomers have long been a challenge due to the low modulus and strength of soft segments. Engineering the chain extender and/or modifying the hard domain are popular strategies for reinforcing TPU elastomers. Here, a strategy based on the thermodynamic principle that the tensile force is strongly related to the Helmholtz free energy for a system with constant temperature and volume is proposed to modify the TPU mechanical performance. The constructed cocontinuous morphology confers to it the highest strength (61.0 MPa) and toughness (156.2 MJ/m³), amounting to 35.3-fold and 11.9-fold improvements, respectively, compared to TPUs constructed with the homogeneous morphology. The significant orientation of morphology during stretching raises the interfacial free energy, which is an analogous mechanism resulting in a higher internal energy. Additionally, this reinforcement technique is scalable, reproducible, and cost-effective and also enriches the fundamental understanding of polymer mechanics.