Fabrication of Well-Ordered Mesoporous Polyimide Films by a Soft-Template Method

A well-ordered mesoporous polyimide film was fabricated by a soft-template method using a microphase-separated structure of an amphiphilic block copolymer (BCP) as a template. Poly(amic acid)s (PAAs) as polyimide precursors and resol as a cross-linker for the stabilization of the nanostructure were found to be selectively miscible with the hydrophilic domain of the template BCP. Their mixture coassembled and formed the desired ordered nanostructures. The composite films tended to form well-ordered nanostructures when PAAs with a flexible domain such as ether or methylene were used. Mesoporous polyimide films were obtained on thermal treatment of the composite films formed via the sequential processes of cross-linking of the resol, imidization of the PAAs, and selective decomposition of the template BCPs. A polyimide film with well-ordered hexagonal-packed cylindrical mesopores was successfully fabricated after the thermal treatment of the composite film based on PAA/polystyrene-block-poly(methacrylic acid)/resol. The domain spacing based on small-angle X-ray scattering was 29.4 nm, and the pore diameter was determined by scanning electron microscopy to be ～19 nm