Labeling a\nPolydiene Elastomer with a π‑Extended\nMechanophore with a Facile and Low Temperature Synthetic Route

Mechanophores are a class of molecules that undergo changes\nin\ntheir optical properties, following a chemical reaction triggered\nby a force. Integrated in elastomeric materials, their ability to\nreport molecular damage opens up a new toolbox to tackle diverse problems\nin polymer mechanics and durability. To be effective, mechanophores\nneed to be included in a load-bearing position, i.e., as a cross-linker\nof networks. This is well-mastered in polyacrylates or polyurethanes\nbut is still challenging in industrially relevant elastomers such\nas polydienes because of the harsh conditions of temperature associated\nwith the typical fabrication of these materials. Here, we functionalize\na damage-reporting π-extended anthracene-maleimide mechanophore\n(DACL) with nitrile oxide (CNO) in order to incorporate it as a cross-linker\nin a poly(styrene-<i>co</i>-butadiene) random copolymer.\nThe incorporation occurs by click chemistry through a mild 1,3-cycloaddition\nbetween the CNO-functionalized DACL and the double bonds present in\nSBR that can take place at room temperature. Finally, we demonstrate\nthe successful activation by force of the DACL mechanophore in the\nSBR by performing a fracture experiment. Given the industrial and\nscientific relevance of the highly entangled polydiene elastomers,\nour study opens up exciting possibilities for damage reporting in\nindustrial rubbers.