Labeling a Polydiene Elastomer with a π-Extended Mechanophore with a Facile and Low Temperature Synthetic Route

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