Circular photo 3D printing enabled by dynamic covalent chemistry

Photocuring 3D printing is an emerging flexible manufacturing technology. Traditional photocuring printing forms polymer networks through chain polymerization, with their main chains consisting of stable carbon-carbon single bonds, making depolymerization and recycling difficult. This study discovered that thiols and aromatic aldehydes can undergo a rapid click reaction under light irradiation. The resulting thioacetal bonds can thermally dissociate under mild conditions, regenerating the original thiols and aromatic aldehydes. Based on this mechanism, we employed this dynamic covalent bond as a building block to establish a novel photocuring polymer network system based on condensation polymerization, achieving closed-loop recycling of the material under mild conditions. Additionally, leveraging the modular tunability of polymer main chains through condensation reactions, this study also achieved effective regulation of the material's mechanical properties. This work is the first to realize closed-loop circular 3Dprinting of high-performance polymer materials, offering a new pathway for the green and sustainable development of additive manufacturing.