Precise Tailoring 3D Printed In Situ Toughening Low‐k Microwave Transparent Structure via Thiol‐acrylate Chain Transfer Behavior

ABSTRACT The unique electromagnetic properties of triazine resins have enabled their growing use in advanced low‐dielectric (low‐ k ) materials. However, their low printability and high brittleness severely restrict engineering applications. Conventional plasticization strategies that enhance printability often compromise dielectric and mechanical properties. Herein, an in situ thiol–acrylate chain transfer‐mediated toughening strategy is introduced for Digital Light Processing (DLP) printing. A triazine‐based resin system comprising THEICTA, isobornyl acrylate (IBOA), and polysulfide rubber (PSR) is formulated into a low‐viscosity (η < 150 cP), highly photosensitive ink, enabling 50 µm resolution printing while preserving a low dielectric constant. Compared with the homopolymer of triazine resin, the topology‐optimized molecular network simultaneously delivers a 462.4% increase in elongation at break, a 640.5% improvement in toughness, a high tensile strength (45.7 MPa), and a low dielectric constant ( ε′ = 2.66). Benefiting from its excellent printability, a printed gyroid lattice‐filled plate (100 µm wall thickness) achieves 92% transmittance at 10 GHz under a 50° incidence angle following structural optimization.