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Mechanically Robust, Self‐Healable, and Highly Stretchable “Living” Crosslinked Polyurethane Based on a Reversible CC Bond

Stimuli‐responsive polymers built by reversible covalent bonds used to possess unbalanced mechanical properties. Here, a crosslinked polyurethane containing aromatic pinacol as a novel reversible CC bond provider is synthesized, whose tensile strength and failure strain are tunable from 27.3 MPa to as high as 115.2 MPa and from 324% to 1501%, respectively, owing to the relatively high bond energy of the CC bond of pinacol as well as the hydrogen bond between hard segments and semicrystalline soft segments. Moreover, the dynamic equilibrium of pinacol enables self‐healing and recycling of the polymer. Interestingly, the dynamic exchange among macromolecules, for the first time, successfully cooperates with solid‐state drawing that applies to thermoplastics, realizing strengthening of thermoset. Meanwhile, the radicals derived from homolysis of pinacol can repeatedly initiate polymerization of vinyl monomers. The fruitful outcomes of this work may create a series of promising new techniques.