Decoupled Covalent Dynamic Exchange Reactions for Closed-Loop Photo-3D-printing

forthcoming

As global dependence on synthetic materials is intensifying, waste-accumulation of end-of-life products has become a major concern. Specifically fast-growing 3D photo-printing technologies present a major challenge as a liquid ink is transformed into a permanently hardened crosslinked photo-polymer that can no longer be recycled. Current photochemical processes that underpin light-based 3D printing processes, however, fail to address the urgently needed closed loop recycling of the resulting 3D materials. Indeed, a fundamental step-change in the underlying, persistently used, chemical technology is urgently needed for 3D printed waste to be effectively and completely depolymerised into the same functional photo-ink for it to be intrinsically re-used in 3D-re-printing. Here, an innovative concept is proposed that offers a ground-breaking solution to the problematic interplay of existing bond exchange reactions currently used in dynamic covalent networks, including 3D printed vitrimers. The idea relies on decoupling the underlying chemical equilibrium by independently regulating bond formation with light, and bond-breaking by temperature. For this, decoupled covalent dynamic exchange reactions (DeCoDERs) will be developed that show selective and sustained covalent bonding/debonding over multiple cycles. The novel DeCoDER systems will be transformed into functional platform building blocks through scalable protocols, allowing for their introduction into dynamic polymer materials. After evaluating the effect of consecutive de- and re-crosslinking of the equilibrium-decoupled material properties, the derived insights will be used to validate the proposed conceptual approach in light-based additive manufacturing. Specifically, a very first 3D photo-print-to-reprint technology will be devised with full recyclability of photo-printed objects into the same initial liquid photo-ink without needing additional chemicals, thereby enabling a direct, truly closed-loop re-print.