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

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/m³), 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.