Breaking performance trade-offs in polyurea by molecular design for integrated self-healing, mechanical strength and flame retardancy

Abstract

Polyurea (PUA) elastomers with superior mechanical robustness, flame retardancy, and self-healing capability are expanding their application in flexible electronics, smart sensors, and electronic skins, anyway a combination of all these performances is still difficult to realize until now. Herein, we report a concept-driven molecular design strategy to construct multifunctional PUA elastomers via the incorporation of an innovatively designed chain extender featuring aromatic units, dynamic covalent bonds, and phosphorus/nitrogen (P/N)-containing groups. This molecular design enables a synergy among mechanical enhancement, flame retardancy, and self-healing that has been rarely demonstrated in previous studies. The aromatic π-π stacking induced straininduced crystallization, enhancing tensile strength by 158.5% and toughness by 181.0% compared to the control samples. Concurrently, the synergistic effect between the aromatic π-π stacking and dynamic covalent bonds granted the PUA high self-healing capability, with a tensile strength recovery of 99.1% after heating at 60°C for 24 h. Additionally, the presence of P/N-containing groups enhanced the flame retardant of the PUA elastomer, achieving a limiting oxygen index (LOI) of 26.8% and a UL-94 V-0 rating, and lowered the rate and total amount of heat and smoke release significantly.Finally, the fabricated silver nanowire/PUA flexible sensor maintained stable electrical signals after 1000 stretching cycles and fire exposure. This work demonstrates a molecular design paradigm for overcoming the long-standing trade-offs among strength, flame safety, and self-healing performance in multifunctional polyurea.