Enhancing Interfacial Compatibility via Solubility Parameter Control for Simultaneous Strengthening and Toughening of Poly(urethane‐urea) Elastomers

The intrinsic trade‐off between strength and toughness remains a central challenge in designing high‐performance elastomers, partly due to the limited understanding of the mechanisms governing mechanical toughening. Here, we propose a solubility parameter‐regulated design strategy for poly(urethane‐urea) elastomers. By combining all‐atom molecular dynamics (MD) simulations with systematic experiments, we systematically elucidate how the solubility of hard segments within the soft matrix governs microphase separation, domain morphology, and ultimately the mechanical properties. Our results reveal that the optimal compatibility between soft and hard segments promotes the coexistence of loose and dense hard domains, enabling simultaneous energy dissipation and load bearing without sacrificing toughness or strength. This synergistic architecture leads to simultaneous enhancements in tensile strength (∼ 77 MPa) and toughness (∼ 290 MJ/m 3 ). Based on the superior elastomer, we further fabricate a stretchable conductor by blending it with silver nanoflakes in the matrix. Due to the improved compatibility, uniform dispersion, and efficient stress relaxation, the conductor maintains high strength and stable electrical conductivity (with negligible resistance change under 70% strain), jointly protecting the conductive architecture against mechanical failure. This work establishes interfacial compatibility engineering as a powerful strategy for designing advanced elastomers for flexible electronic applications.