Synthesis of room temperature ionic liquids based random copolyimides for gas separation applications

Random copolyimides were synthesized using diamino functional room temperature ionic liquid (RTIL) and were characterized. Specifically, a diamino functional RTIL, 1,12-di[3-(3-aminopropyl) imidazolium] dodecane bis[(trifluoromethyl)sulfonyl] imide ([C12(DAPIM)2][Tf2N]2), was reacted with 2,2-bis(3,4-carboxylyphenyl) hexafluoropropane dianhydride (6FDA) and m-phenylenediamine (MDA) to form random cooplyimides with a [C12(DAPIM)2][NTf2]2 concentration varying from 10 to 30 mol%. Incorporation of [C12(DAPIM)2][NTf2]2 within the 6FDA–MDA backbone resulted in decreases in the polymer thermal stability, glass transition temperature, d-spacing, fractional free volume and increments in density. The gas permeability, solubility and diffusivity of the random copolyimides decreased and the permeability selectivities increased compared with the pure 6FDA–MDA polyimide.