Constructing\nStrong and Tough Polymer Elastomers via\nPhotoreversible Coumarin Dimer Mechanophores

Advanced\nelastomers with outstanding strength, toughness, and reusability\nhold significant potential for diverse applications. Using photochemistry\nand mechanochemistry to develop such materials has become a very effective\nstrategy. Here, we report that photoreversible coumarin-based mechanophores\nthat can make force-/light-triggered cycloreversion are chemically\nincorporated into polyurethane elastomers to simultaneously enhance\ntheir strength and toughness. Coumarin dimer mechanophore cross-linkers\nare formed in the polyurethane elastomer after exposure to 365 nm\nirradiation, leading to networks with dramatically enhanced mechanical\nproperties. The tensile strength of the HNA-PU<sub>2000</sub> elastomer\nwith coumarin dimer mechanophore cross-linkers could increase from\n13.9 to 26.9 MPa, elongation at break from 726 to 1053%, and toughness\nfrom 25.6 to 119.7 MJ·m<sup>–3</sup>, in contrast to its\ncounterpart HNA-PU<sub>2000</sub> elastomer without coumarin dimer\nmechanophores. Additionally, the polyurethane elastomer exhibits a\ndecent reusable capability via force-/light-triggered cycloreversion\nof coumarin dimer mechanophores under mechanical stress or 254 nm\nirradiation. This mechano-/photochemical strategy to improve strength,\ntoughness, and reusable capability of elastomers provides a facile\napproach for the development of high-performance elastomer materials.