Preparation and gas separation properties of spirobisbenzoxazole-based polyimides.

[Display omitted] • Novel spirobisbenzoxazole-based polyimides of intrinsic microporosity were prepared. • The polyimides showed good solubility, excellent thermal and mechanical properties. • Discuss the rotation restriction and thermal annealing process on gas permeation behavior. Improving the processability and permeability of aromatic polyimides is a prerequisite for promoting the application in the field of gas separation membranes. Here, a series of novel spirobisbenzoxazole-based polyimides were synthesized. The novel spirobisbenzoxazole unit showed a larger rigid step size than the reported spirobisindane unit, which more effectively destroyed the molecular packing. As a result, the obtained aromatic polyimides showed good organic solubility and significantly improved gas permeability. Such polyimides were also considered as polymers of intrinsic microporous (PIMs) with ultra-micropore distribution of 5 ∼ 7 Å and high BET surface areas ranging from 373 to 449 m2/g. Meanwhile, the obtained polyimide membranes exhibited excellent thermal properties (T g > 400 °C) and outstanding mechanical properties (σ > 100 MPa). The effects of rotation restriction and thermal annealing process on gas permeation behavior were also studied. [ABSTRACT FROM AUTHOR]