Realizing Vat‐Photocycloaddition 3D Printing with Recyclable Synthetic Photorheological Silicone Fluids

Abstract Synthetic silicone rubbers are finding a broad spectrum of applications, yet there is a demand for developing greener silicone rubbers with processability, recyclability, and reversible tunability in their mechanical properties. Here, a recyclable photorheological silicone fluid (RPSF) is developed, which realizes completely reversible wavelength‐selective liquid–rubber conversion upon photoirradiation, relying on the reversible photocycloaddition of coumarin upon alternating irradiation of light with wavelengths of 365 (UV 365 ) and 254 nm (UV 254 ). Rheological studies demonstrate that the storage modulus of the developed RPSF increases by a factor of more than 100 000 upon UV 365 irradiation to reach 20–50 kPa, while it decreases to ≈0.01 kPa upon UV 254 irradiation. The reversibility of the photocycloaddition of coumarin enables the application of RPSF as a photodismantlable adhesive. Furthermore, unprecedented vat‐photocycloaddition 3D printing of silicone rubber is realized by taking advantage of the excellent photocurability, that is, the dramatic increase in viscoelasticity upon UV 365 irradiation.