Wavelength-Dependent\nDynamic Behavior in Thiol–Ene\nNetworks Based on Disulfide Exchange

While latent catalysts have become a well-established\nstrategy\nfor locally and temporally controlling bond exchange reactions in\ndynamic polymer networks, there is a lack of inherently tailorable\nsystems. Herein, we introduce a thiol–ene network based on\ndisulfide exchange that alters its dynamic properties as a function\nof the color of light used during the curing reaction. For this purpose,\nselected allyl-bearing disulfides are synthesized, which are transparent\nat 450 nm but undergo disulfide scission upon 365 nm light irradiation,\nas confirmed by UV–vis and EPR measurements. Incorporated into\na thiol–ene resin, the wavelength used in the curing reaction\ndefines the dynamic properties of the obtained photopolymer. At 450\nnm, photocuring yields a dynamic network with disulfide bonds, which\nrelaxes to 63% of its original stress within 112 s at 160 °C\n(without the requirement of an external catalyst). In contrast, curing\nwith 365 nm light induces disulfide scission yielding photopolymers,\nwhich contain predominately monosulfidic links. The permanent nature\nof the links effectively prevents relaxation of the polymer within\na reasonable period of time, confirming the successful alteration\nof its dynamic properties simply by the color of the light source\nused.