Ionic Polyurethanes as a New Family of Poly(ionic liquid)s for Efficient CO2 Capture

Carbon dioxide (CO2) levels are continuously growing, and CO2 is believed to be a significant contributor to global warming and climate change. Therefore, there is a great interest in the development of highly efficient technologies to curb CO2 emissions of current energy sources. In this context to combat such issues, poly(ionic liquid)s (PILs) offer an extremely versatile and tunable platform to fabricate a wide variety of sorbents for CO2 capture. To date, the majority of poly(ionic liquid)s studied for CO2 capture is related to carbochain polymers (acrylate and styrene polyelectrolytes), while it is generally accepted that polymers with more basic backbones such as amides, urethanes or amidoxines Aar! considerably enhance the CO2 absorption capacity. Thus, a series of novel high molecular weight (M-n = (3.4-21.0) X 10(4)) ionic polyurethanes (PUs) have been prepared using four different ionic diols based on ammonium, quinuclidinium, diquinuclidinium and imidazolium cations. Furthermore, a range of ionic PUs bearing 13 different counteranions including classical ((CF3SO2)(2)N, BF4, PF6, and N(CN)(2)) and less encountered anionic species such as acetate, lactate, tetracyanoborate, bis(pentafluoroethylsulfonyl)amide, CF3SO2-N-CN and MeHal(n) (Me = Fe(III), Cu(II), Zn(II), Hal = Cl, Br) was obtained through the ion exchange reactions using the same bromide PU precursor. This allowed to separately isolate the effect of diisocyanate, cations and anions nature on physical properties of ionic PUs. The obtained poly(ionic liquid)s demonstrate high thermal stability (up to 275 degrees C), have glass transition temperatures in the range of 30-78 degrees C and show remarkable CO2 capture. It was found that ionic PUs incorporating diquinuclidinium cation and CH3COO or BF4 anions exhibit the highest CO2 sorption (18.25 and 24.76 mg/g at 273 K and 1 bar), not only overcoming the CO2 capture reported to date for linear PILs, but even surpassing the highest value known for cross-linked meso-porous poly(ionic liquid)s (20.24 mg/g at 273 K and 1 bar). Altogether, this paper demonstrates the potential of poly(ionic liquid)s as efficient designing materials for CO2 capture.