Circular 4D Printing of Multi-Functional Polymers

To overcome the irreversible cross-linking and constrained performance in conventional 3D printing materials, we propose a molecular design strategy integrating dynamic covalent bonds and polymerizable carbon-carbon double bonds for 4D (4-dimensional) printing. Using programmable cardanol-based polyurethane acrylates with dynamic hindered urea bonds, this system enables rapid network formation for high strength while polymerizable carbon-carbon double bonds relieve stress and balancing rigidity, toughness, and self-healing. The system was integrated into an additive manufacturing process, thus enabling the creation of 3D parts that transform in response to external stimuli over time (i.e., 4D printing). These 4D-printed parts exhibits excellent processability via digital light processing, allowing the fabrication of complex architectures. Upon exposure to appropriate stimuli, they demonstrate integrated functionalities including shape memory, thermochromism, and information encryption. Critically, the reversible urea bonds allow mild chemical degradation and closed-loop recovery of selected raw materials, with recovered resin maintaining printability and functionality. The material also demonstrates notable photothermal conversion. This work provides a sustainable strategy for high-performance, 4D printing in flexible electronics and anti-counterfeiting.