Metastable Polymers for Circular 3D Printing.

Reducing waste and enabling material reuse are central goals for sustainable advanced manufacturing. In light-based 3D printing, this requires moving beyond permanent networks toward systems that can be easily returned to their original molecular building blocks, while preserving good performance. Here, a shift toward metastable, 3D printable polymers is introduced, which are intrinsically programmed for controlled depolymerization under mild conditions, enabling circular recovery. This concept is realized using self-immolative polymers (SIPs), which undergo triggered, domino-like depolymerization upon activation of a specific labile unit. These polymers are formulated for high-resolution digital light processing 3D printing, yielding mechanically robust structures. Upon exposure to a defined trigger, the printed networks rapidly (in seconds) and completely disassemble under ambient conditions, regenerating their pristine monomers. These are recovered in near-quantitative yield and subsequently reprocessed into chemically identical printable polymers. This metastability-driven approach establishes a transformative pathway for circular 3D printing.