Blend membranes of ionic liquid and polymers of intrinsic microporosity with improved gas separation characteristics

Abstract

In 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.