Post‐Baking‐Induced Self‐Locking Interpenetrating Networks Strengthen 3D‐Printed Polyimide Architectures With Enhanced Thermal and Mechanical Properties

Abstract Addressing the inherent challenges of weak interlayer bonding and anisotropic mechanical properties in layer‐by‐layer fabrication processing is pivotal for mitigating the brittleness of 3D‐printed structures and enhancing their heat deflection temperature (HDT). In this study, molecular engineering strategies are employed to design and synthesize novel high‐performance photosensitive polyimide inks, incorporating both methacrylate (photo‐curable) and benzoxazine (thermal cross‐linkable) functional groups. During the 3D printing process, ultraviolet exposure initiates the photopolymerization of methacrylate, forming flexible covalent networks. Subsequent thermal treatment induces the ring‐opening polymerization of benzoxazine, resulting in the formation of a rigid phenolic‐aromatic network that shuttles the 3D architecture. Mechanistic investigations reveal that the development of a dual interpenetrating network comprising both soft and hard phases significantly enhances interlayer bonding and eliminates anisotropy in printed materials. Consequently, the 3D polyimide structures exhibit exceptional thermal stability under load (HDT > 165 °C), superior isotropic mechanical properties (elastic modulus > 1.1 GPa, and elongation at break > 8.5 %), and high dimensional accuracy (shrinkage <1%). This approach establishes a general platform for the rapid fabrication of high‐performance 3D structures with robust interlayer connectivity, offering a promising solution to the limitations of conventional additive manufacturing techniques.