Photochemically induced oxidative surface modification of polyimide films

Polyimide membranes that contain both the phthalimide chromophore and abstractable hydrogens undergo photochemically‐induced oxidative surface modification when they are irradiated with ultraviolet (UV) light for 0.5–30 min in air. The reaction requires 200–300 nm light and the presence of oxygen, and the surface‐modified membranes show much higher oxygen/nitrogen selectivities than the untreated films. A mechanism for the photochemical reaction that is based on the photochemistry of structurally‐similar monomeric phthalimides is proposed. The observed selectivity increases can also be explained by this mechanism.