Ultraviolet-Shielding Recyclable Polymer Film Fabricated via Knoevenagel Condensation

Ultraviolet (UV) radiation presents serious risks to human health, materials, and the environment. UV-shielding materials play a vital role in health, industry, and environmental protection. Previously, we have developed a facile method to construct recyclable thermosetting polymer through the Knoevenagel condensation (KC) reaction. Herein, an ultraviolet-shielding recyclable film, P-TFMBTC-PCL, was fabricated through the KC reaction by introducing dynamic covalent bonds into the cross-linking network. We initially developed a cross-linking agent using vanillin and 1,3,5-benzenetricarbonyl chloride as starting materials. Subsequently, P-TFMBTC-PCL was synthesized through KC reaction of the cross-linking agent with polycaprolactone (PCL). In cyanoacetic acid end-modified PCL, active methylene groups react with aldehyde groups from the cross-linking agent to create dynamic C═C bonds. Consequently, this film exhibits an exceptionally tensile strength of 18.78 MPa and an elongation at break of 959.11%. Also, the dynamic exchange of dynamic C═C bonds confers both reprocessability and recyclability to the obtained thermosetting materials. Additionally, the C═C bonds expand the conjugation domain of the aromatic ring, endowing the film with ultraviolet resistance that blocks 100% of the ultraviolet rays from 200 to 432 nm. Overall, this dynamic networked film exhibits significant potential in the packaging, agriculture, and automotive industry.