Visualization of mechanochemical polymer-chain scission in double-network elastomers using a radical-transfer-type fluorescent molecular probe†

Double-network (DN) elastomers are renowned for combining stiffness and toughness. Their exceptional physical properties have garnered significant attention in recent years. However, the fracture phenomena in DN elastomers are much less understood than those in DN gels due to the limited scope of visualization methods. Here, we demonstrate the visualization of sacrificial bond cleavage in DN elastomers during elongation by adding a diarylacetonitrile (DAAN) derivative as a radical-transfer-type fluorescent molecular probe, which enables the visualization of polymer-chain scission without altering the mechanical properties. A tensile test of the DN elastomers that contain DAAN revealed that mechanoradicals are generated from the entire elongated region of the elastomers in the strain-hardening region. In contrast, DN gels generate mechanoradicals only at the necked region. This method is expected to accelerate the investigation of the fracture properties of various DN elastomers.