A team of researchers from the Institute of Science Tokyo (Science Tokyo), led by Professor Hideyuki Otsuka, along with Dr. Kuniaki Ishizuki and Assistant Professor Akira Takahashi, has developed a new method to make existing polymers sensitive to mechanical stress. Their work, published in the journal Advanced Materials on August 17, 2026, introduces a way to add stress-responsive fluorescence to a polymer without chemically altering it. This technique involves blending a special type of polymer, called a mechanophore-containing polymer, with a common material known as styrene–butadiene–styrene (SBS) block copolymer. The result is a material that can visibly signal when it is being stretched. SBS is a block copolymer, meaning it is made of different polymer segments joined in distinct blocks. It contains rigid polystyrene (PS) sections interspersed within softer polybutadiene sections, giving the material both hard and flexible properties. The researchers created a version of PS that included a molecule called tetraarylsuccinonitrile (TASN), a type of mechanophore, and then blended it with commercially available SBS. Because the new polymer shares the same chemical makeup as the PS sections in SBS, it naturally separates and localizes within those rigid regions. This allows mechanical force to be efficiently directed to the mechanophores when the material is stretched, without changing the original SBS structure. When the material is stretched, the TASN mechanophore reacts to the mechanical stress by breaking certain chemical bonds, creating highly fluorescent molecules called diarylacetonitrile radicals. These radicals emit a visible yellow-green glow when exposed to ultraviolet light, making the mechanical response visible to the naked eye. Tests showed that films made from the modified SBS blend displayed clear fluorescence after being stretched, while unmodified SBS showed no such response. This fluorescent signal provides a direct way to see when and where mechanical stress is applied to the polymer. The team also discovered that the intensity and behavior of the fluorescence could be adjusted by varying the amount and size of the mechanophore-containing polymer used. Importantly, the mechanical properties of SBS were either maintained or even improved in some cases. The fluorescence response was also reversible — after stretching, the glow faded as the radicals recombined, but it reappeared when the material was stretched again after a 24-hour rest. Additional experiments showed that the material became more responsive to mechanical stress as it neared its breaking point, suggesting that the stress was increasingly directed to the rigid PS sections during deformation. This method provides a practical way to add stress-sensing capabilities to existing polymers without complex chemical changes. In the future, the approach could be applied to other types of polymers and functional molecules, potentially leading to materials that can visually indicate when they are experiencing stress or damage. This could be useful in fields such as engineering, medicine, and materials science, where detecting mechanical stress is crucial for safety and performance.