Dual-templated hierarchical porous polyimide coatings with improved moisture resistance and mechanical integrity

Reliable dielectric performance and long-term service stability of polymer insulating coatings under humid environments remain significant challenges, as moisture ingress often induces polarization, accelerates property deterioration, and compromises coating reliability. Herein, a dual-templating strategy is developed to fabricate hierarchical porous polyimide (PI) coatings with enhanced moisture resistance and mechanical integrity. By combining breath figure-induced microporous arrays with polyethylene glycol (PEG)-assisted nanoscale templating, a well-defined multiscale porous architecture is constructed, consisting of ordered honeycomb-like micropores and abundant nanopores distributed within the pore walls. The hierarchical porous structure effectively regulates moisture transport and suppresses water uptake, leading to significantly improved environmental stability under humid conditions. The optimized m-PI-15 coating exhibits a low water absorption of 0.905% and maintains excellent stability after moisture exposure, with only minor increases in dielectric constant (Δκ = 0.156) and dielectric loss (Δtanδ = 0.004). Meanwhile, the coating demonstrates enhanced mechanical performance, achieving a tensile strength of 117.42 MPa, an elongation at break of 70.35%, and a tensile modulus of 1.915 GPa. The superior performance is attributed to the synergistic effect of ordered micropores and interconnected nanopores, which increase moisture diffusion tortuosity while promoting efficient stress redistribution. In addition, the porous coating can be reversibly constructed and removed, enabling repeated structural reconfiguration without significant deterioration in moisture resistance or mechanical properties. This work establishes a clear structure–property relationship for hierarchical porous PI coatings and provides a simple, scalable approach for designing moisture-resistant functional coatings for applications in humid and demanding service environments.