Self-crosslinking of bromomethylated 6FDA-DAM polyimide for gas separations

The CO2-induced plasticization effects impose detrimental effects on polymeric membranes separation performance. To address this issue, a high-performance crosslinked brominated 6FDA-based polyimide (BMPI) is developed in this work, exhibiting highly suppressed plasticizing effects. The permeability and selectivity of polyimide precursor membranes are tuned by introducing bromine atoms into the polyimide structure, creating a best performing membrane with bromination degree of 60%. The membrane CO2 permeability reaches 395 Barrer, and the selectivity of CO2/CH4 increases from 22.0 for a non-brominated analogue to 26.0. The debromination induced crosslinked BMPI membranes are achieved upon thermal treatment within the temperature range of 150 °C–350 °C with varied crosslinking degree, resulting in large differences for the membrane separation performance. The completely crosslinked BMPI treated at 350 °C for 10 h demonstrates high CO2 permeability of 483.6 Barrer and the CO2/CH4 selectivity of 26.0. Most importantly, the crosslinking reaction greatly stabilizes the membrane performance against plasticization under high CO2 feed pressure. Compared with the non-crosslinked membranes with a plasticizing pressure of 150 psia, the plasticization for the crosslinked membrane occurs at high CO2 pressure of 600 psia. This study provides a facile approach for the preparation of high-performance gas separation polymeric membranes with enhanced plasticization resistance.