Photo-Reversible Coumarin-Based Networks With Tailorable Properties for Extrusion 3D Printing and Adhesive...

Harnessing the spatiotemporal precision of light, photo-reversible chemistries offer an approach to move beyond static fabrication toward dynamic materials. This study reports the synthesis and characterization of coumarin end-capped urethane based poly(ethylene glycol) (CUP) materials. The reversible [2+2] cycloaddition of coumarin allows for network formation within 5 min of 365 nm irradiation (max conversions $>90\%$ ), while enabling $>70\%$ cleaving after 30 s of <300 nm irradiation. Rheological assessment confirms the viscoelastic liquid precursor's suitability for extrusion-based printing at ambient temperature, yielding high resolution prints with excellent shape fidelity. Finally, the CUP material is exploited as a strong, reversible and tunable light-responsive adhesive for glass substrates, showing adhesive strengths between 53 $\pm$ 15 and 1717 $\pm$ 367 kPa depending on the irradiation time.