Gas permeability and permselectivity of fluorinated polybenzoxazoles

Gas permeability and permselectivity are investigated for polybenzoxazoles from bis(3‐amino‐4‐hydroxyphenyl)‐1,1,1,3,3,3‐hexafluoropropane (BAHHP) and aromatic diacid chlorides. Effects of thermal cyclization on the permeation properties are also investigated. The polybenzoxazole from BAHHP and 4,4′‐(1,1,1,3,3,3‐hexafluoroisopropylidene)dibenzoyl chloride (HFDB) displays high performance for CO2/CH4 separation ( {article}{empty}{document}P_ CO₂{document} = 6.1 × 10−9 cm3 (STP) cm−1 s−1 cm‐Hg−1, and {article}{empty}{document}P_ CO₂ / P_ CO₂ P_ CH₄ . - P_ CH₄{document} = 38 at 35°C). The polybenzoxazole from BAHHP and 2,6‐naphthalene dicarbonyl chloride displays high performance for H2/CO or H2/CH4 separation ( {article}{empty}{document}P_ H₂{document} = 2.4 × 10−9 cm3 (STP) cm−1 s−1 cm‐Hg−1, {article}{empty}{document}P_ H₂ / P_ H₂ P_ CO . - P_ CO{document} = 71, and {article}{empty}{document}P_ H₂ / P_ H₂ P_ CH₄ . - P_ CH₄{document} = 250). Permeation properties for the polybenzoxazole from BAHHP and HFDB are close to those for a polyimide of similar chemical structure. The permeation properties are discussed in connection with packing density and local segmental mobility.