Nomadic Molecular Key‐Driven Instantaneous Covalent Reconstruction Enables Ultrahigh Impact‐Stiffening Polymeric Armor

ABSTRACT Impact‐stiffening materials hold great promise in safeguarding human safety and apparatus integrity, serving as intelligent armor to mitigate transient impact and damage. However, high activation strain/rate, stiffening hysteresis, and inefficient energy dissipation of current materials pose significant challenges for matching extreme events. Herein, we report a nomadic molecular key‐driven ultrahigh impact‐stiffening strategy that leverages strain‐rate‐sensitive and covalent‐active molecules to trigger covalent reconstruction and nanodomain agglomeration within polymers. Our design employs poly(styrene‐thioctic acid) (PSTx) with a few thioctic acids (TA) as a critical stiffening key, in which disulfide/hydrogen bonds form energy‐dissipating multi‐networks, while phenyls act as precursors for physical crosslinking. Distinct from conventional mechanisms, force‐activated TA functions as a molecular key that rapidly induces covalent crosslinking and phenyl nanodomain resembling, effectively “locking” networks and blunting cracks to achieve efficient impact‐resistance. PSTx exhibits ultralow relaxation time (15.8 ms), exceptional stiffening response (2925 times), and stretchability over 4000%. Even at low strains/rates of 2000 s −1 , it achieves high modulus (5.8 GPa), record strength (84.3 MPa), and excellent energy dissipation (12.4 MJ/m 3 ), yielding 97% impact‐force reduction. PSTx is processable into various wearable composites with outstanding impact force attenuation (+957%) and puncture resistance (+360%). This work resolves challenges of activation thresholds and stiffening hysteresis in impact‐stiffening materials, providing a molecular key‐switchable paradigm for intelligent systems.