AbstractIn the present work an attempt has been made for the first time to blend polymers of intrinsic microporosity, specifically PIM-1 with the ionic liquid (IL) [C6mim][Tf2N] in order to improve the gas separation properties of PIM membranes. The blend membrane led to a slightly reduced permeability and improved the selectivity. However, due to the lack of compatibility between PIM-1 and the IL, the polarity of PIM-1 had to be tuned. Blending and chemical modifications of PIM-1 were studied to achieve a good distribution of the IL in the polymer matrix. The first method included physical blending of PIM-1 with poly(ethylene glycol) (PEG) as compatibilizer and the second method included copolymerization of PIM-1 monomers with a PEG containing anthracene maleimide comonomer (CO). The copolymerization technique yielded better polymer-IL compatibility in the IL concentration range 2.5 – 10 wt% compared to the blends of PIM-1 with PEG and IL. The incorporation of the IL into the copolymer of PIM-1 (PIM-COP) matrix resulted in an improvement of CO2 / N2 selectivity from 19 to 30 at 30 °C, in combination with a relatively high CO2 permeability coefficient (above 800 Barrer). The studied polymer-IL composites are good candidates for the use as selective layer materials in thin film composite membranes aimed at e.g. post-combustion gas separation.