A hydroxyl-containing polyimide (PI) based on 4,4'-(Hexafluoroisopropylidene) diphthalic anhydride (6-FDA) and 2,2-Bis(3-amino-4 hydroxyphenyl) hexafluoropropane (Bis-APAF) was successfully synthesized using the one-step high-temperature polycondensation method to obtain a soluble, transparent, and cross-linkable PI. All its solubility, thermal properties, mechanical properties, and optical properties were investigated. In order to enhance the chemical resistance of PI, the PI could be cross-linked chemically and underwent a cross-linked reaction with three different cross-linkers, including 1,4-phenylene diisocyanate (1,4-PDI), 4,4'- oxybis (phenyl isocyanate), and resorcinol diglycidylether cross-linkers. The chemical structures of the polyimide and cross-linked polyimides were confirmed using FTIR spectra. The PI showed excellent solubility in common organic solvents, good mechanical properties (tensile strength of 51.06 MPa), an optical transparency of approximately 90% (89.37%) at a wavelength of 550 nm, and it can convert to polybenzoxazole (PBO) at high temperatures. The inherent viscosity of the PI was 0.35 dL/g as measured in N,N-dimethylacetamide (DMAc) solvent at 30oC. The cross-linked membranes showed good chemical resistance in organic solvents and higher tensile properties (tensile strength exceeding 76.02 MPa) as compared to the pure PI but showed inferior optical properties that were reduced after cross-linking reaction. The 1,4-PDI, 4,4'- oxybis (phenyl isocyanate) cross-linkers enhanced the thermal properties of the membranes while the 4,4'- oxybis (phenyl isocyanate) cross-linker reduced them.

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