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

Abstract

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.

Fabrication of Mesoporous Polyimide Composite Films by a Soft-Template Method Followed by Ozonolysis

“…5c) showed that the pore size increased to 50~100 nm and the order disintegrated which agrees with the SAXS result. The result reflects a relatively low glass transition temperature of the PAA (183 °C) [36]. Optimization of the primal structure of PAA would prevent the collapse of the nanostructure.…”

“…Given the background, the facile fabrication method of obtaining ordered mesoporous polyimide films by developing the soft-template method was reported [29][30][31][32][33][34][35][36]. In this method, an amphiphilic block copolymer with a narrow polydispersity and a well-defined composition ratio was used as a template to make ordered nanostructure.…”

“…Furthermore, this method has the potential to form multiple morphologies such as spheres, cylinders, lamellae, and bicontinuous structures by the control of their volume fraction. However, the remaining task of decomposing the template block copolymer at high temperature (~380 °C) might cause a collapse of the nanostructure [36]. Therefore, a much mild porosification method was strongly desired.…”

“…In this study, poly(1,4-isoprene)-block-poly(2-vinylpyridine) (PI-b-P2VP) was used as a template block copolymer that consists of a degradable hydrophobic segment, polyisoprene (PI), and a hydrophilic segment, poly(2-vinylpyridine) (P2VP), which is compatible with PAA and resol. A PAA based on 4,4'-oxydiphthalic anhydride (ODPA) and 1,3-bis(3-aminophenoxy)benzene (MAPB) was used as a source of polyimide because such a flexible primary structure was advantageous for the formation of ordered nanostructures as a result of a previous study [36]. PAA composite films were prepared by mixing of the PAA, the template block copolymer, and resol, and then these nanostructures were characterized by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM).…”

Synthesis and Carbonization of Polyimide Nanoparticles Modified with Long Alkyl Chains Aspiring to Non-precious-metal Fuel Cell Catalysts

“…Polyimides (PIs) exhibit excellent heat resistance, mechanical strength, chemical stability and electrical resistivity and are utilized as aerospace and electronic materials [1][2][3][4]. In terms of expanding their applicability, controlling the morphology of polyimides is an important research topic [5][6][7][8][9]. Especially, spherical PI nanoparticles have drawn much attention due to their potentials for next generation materials, such as catalysis, nanoreactors, nanofillers, drug delivery carriers [10][11][12][13][14].…”