Ionicpolyimide membranes containing Tröger's base: Synthesis,microstructure and potential application in CO₂separation

XiaochenXu, Jingjing Wang, Jie Dong*, Hai-Bei Li, Qinghua Zhang, Xin Zhao*

Journalof Membrane Science, 2020, 602: 117967.

https://doi.org/10.1016/j.memsci.2020.117967

Inan attempt to obtain polymeric gas separation membranessimultaneously with high permeability and high selectivity, herein,series of novel ionic polyimides containing Tröger's base (TB) unithave been synthesized following an efficient synthetic methodologyincluding the ionization of imidazole moiety and ion-exchangereaction. The effects of polyimide backbone structure, bonding modeof the ion pair and ion species on microporous structure, molecularpacking behavior, mechanical property and gas separation property ofthe prepared ionic polyimide membranes were investigated. Our resultsreveal that the incorporated TB unit with rigid and in-built aminestructure and an external attractive interaction for CO₂of particular ions have a synergistic effect on increasing thepermeability and selectivity of polyimide membranes by retardingchain packing and increasing CO₂affinity. Typically, the prepared ionic membranes modified by thelateral substituted bis(trifluoromethanesulphonyl)imide ([TFSI]-)show a maximal CO₂permeability of 90.1 Barrer with the CO₂/CH₄and CO₂/N₂selectivities of 37.5 and 21.9, respectively, which is around 120%higher than that of its parent polyimide membrane in CO₂permeability. Meanwhile, the covalent integration of ions inpolyimide backbone creates a sufficient stability of the membranesand endows them with tensile strengths of over 50 MPa, more superiorthan those of most reported supported ionic liquid membranes (SILMs)for gas separation applications. This study extends a new method forconstructing high permeable polyimide materials for CO₂gas separation.