Natural gas purification and olefin/paraffin separation using cross-linkable 6FDA-Durene/DABA co-polyimides grafted with α, β, and γ-cyclodextrin

► Cross-linkable co-polyimide (6FDA-Durene/DABA (9/1)). ► Various sizes of cyclodextrin are grafted to the polyimide matrix. ► New flexible and high-performance gas separation membranes. ► A high CO2 permeability of 4211 Barrer with a CO2/CH4 selectivity of 22 is achieved. ► A high C3H6 permeability of 521 Barrer with a C3H6/C3H8 selectivity of 18 is achieved.