Tailoring the gas transport properties of network polyimide membranes by bromination/debromination

Constructing membranes that possess both exceptional gas transport property and strong resistance to CO 2 -induced plasticization is a crucial need in membrane separation , yet it still stands as an ongoing challenge. In present study, we firstly added the bromine atom into the 2, 2′-bis(trifluoromethyl)benzidine (TF) to synthesis two new bromine substituted diamines, and subsequently one of the brominated diamines was employed as a comonomer alongside commercial tris(4-aminophenyl)amine (TAPA) and dianhydride 6FDA to prepare the network polyimide (PI) membrane via copolymerization . Following this, these new brominated PIs would undergo debromination process during the subsequent heating treatment. As a result, the bromination/debromination effect created new microporosity , which increased the d-spacing and BET surface area of the membrane, thereby largely enhancing the crosslinked PI membrane’s gas separation performance. Moreover, the robust network structures achieved through in-situ crosslinking way, derived from a segment of trifunctional TAPA monomers , enhance the resultant membrane's resistance to CO 2 plasticization issue. An exemplified membrane referred to as 6 F-TA/TF-dBr-450 membrane displays outstanding CO 2 /CH 4 separation capabilities, with a CO 2 permeability of 1420.56 Barrer and a CO 2 /CH 4 selectivity of 39.67, surpassing the 2008 Roberson upper bound by a considerable margin. Besides, this membrane demonstrates outstanding durability against CO 2 -induced plasticization, showcasing its strength under pressures of at least 35 Bar.