Synthesis, characterization and properties of polyimides with spirobisbenzoxazole scaffold structure

Novel diamines containing spirobisbenzoxazole scaffold structure were successfully synthesized. These diamines were homopolymerized with commercial 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and cyclohexanedianhydride (H'PMDA) to prepare a series of benzoxazole based polyimides (PBOIs). The obtained PBOIs exhibited good organic solubility and outstanding thermal properties, including glass transition temperature (Tg) of 355-400 °C and 5% thermal decomposition temperatures (Td5%) of 474-490 °C. Meanwhile, these polymer films exhibited excellent mechanical strength, such as tensile strength of 79.4-92.1 MPa and elongation at break of 19.5%?31.2%. In addition, such PBOIs have been proved to be novel microporous polymer with pore width distribution of 5-7 Å and BET surface area of 281-378 m2/g. The permeability-selectivity relationship of H'PMDA based PBOIs was close to the 2008 Robeson upper bound for CO2/CH4 and O2/N2 gas pairs, showing promise in the field of gas separation. © 2022 Elsevier Ltd