Bound water as a kinetic crosslinker for bio-inspired impact-stiffening polymers.

Developing high-performance impact-stiffening polymers that are broadly applicable across chemical systems remains a key challenge, as existing designs rely on meticulously engineered molecular motifs. Inspired by water's role in biological impact resistance, we introduce a generalizable biomimetic paradigm. We transform water-commonly considered a property-limiting plasticizer-into an active, rate-sensitive cross-linker by structurally confining bound-water networks within proton-rich polymer scaffolds. Programming their dissociation kinetics enables a sharp, reversible soft-to-rigid transition under impact via kinetic freezing. This design, demonstrated in a poly(thioctic acid)-based system, concurrently achieves outstanding energy dissipation, self-healing, and strong adhesion. Crucially, it bypasses de novo synthesis of specialized motifs and is applicable across diverse polymer backbones, establishing programmable water dynamics as a versatile principle for adaptive polymeric materials.