High‐Durability Anti‐Fog Coating Based on Carboxyl‐Promoted Anti‐Yellowing Cross‐Linkable Hybrid Adhesive Material of Polyvinyl Alcohol and Polyimide

Abstract A novel polyimide (PI) with a carboxyl side group is synthesized. Cross‐linked hybrid films are prepared by adding a small amount of PI to polyvinyl alcohol (PVA), causing esterification and etherification reactions during the convection drying process. The physical properties of the hybrid films vary significantly depending on the PI content and drying temperature. The higher the PI content and the drying temperature, the higher the cross‐linking density. In particular, the hybrid film (PVA/PI4 ₁₇₀ film) containing 4 wt.% PI relative to PVA can most effectively suppress the thermal decomposition of PVA during the high‐temperature drying process at 170 °C, preventing yellowing. When PI exceeds 6 wt.% relative to PVA, phase separation occurs, and the hybrid film becomes opaque. PVA/PI4 ₁₇₀ film demonstrates excellent water resistance, tensile strength, surface friction resistance, impact resistance, and glass adhesion properties due to its appropriately cross‐linked structure. No fogging is observed when the coated surface is exposed to water vapor. The present PVA/PI hybrid film is expected to be used semi‐permanently as an anti‐fog coating material, even in high‐temperature and high‐humidity environments. This research will serve as a technical guide for the development of advanced functional films based on PVA and PI in the future.