Danno nella gomma stirene-butadiene: sintesi di un meccanoforo pi-AM modificato e design di un nuovo metodo di incorporazione

Soft materials are characterized by their remarkable property of a complete reversibility to their initial shape after undergoing mechanical stress. Due to this, they find widespread application in various fields such as automotive, high-tech or biomedical applications. Despite their common usage, their failure mechanism is not completely clarified, due to the complex fracture mechanism involving crack propagation and energy dissipation. Mechanophores are a new class of molecule that provides a solution to this gap by acting as probes that respond to mechanical activation, giving a detectable quantitative signal. This enables a correlation between macroscopic material failure and microscopic behaviour when incorporated in polymers. However, their usage is still confined to a limited range of elastomers, due to their relative fragility which is not compatible with the harsh conditions typically associated with more industrially relevant elastomers’ fabrication, such as polydiene rubbers. To expand that scope, we developed a nitrile oxide modified version of an existing pi-extended anthracene-maleimide (pi-AM) mechanophore that we successfully incorporated in a styrene-butadiene rubber (SBR) matrix in mild conditions, by targeting the available double bonds in the chains. Then, when submitted to a mechanical force, labelled rubber emits a fluorescent signal. This was achieved through two distinct methods: cross-linking free SBR chains using the modified probe alongside a bis-nitrile oxide cross-linker we synthesised and infusing it into pre-vulcanized SBR materials. Through a quantitative analysis, performed using confocal microscopy, we were able to precisely evaluate damage extension on a microscopic scale, leading to important advancements in the study of damage mechanisms within industrial rubbers.