Plasticization- and Aging-Resistant Phenolphthalein-Based Thermally Cross-Linked PIM Polyimide Membranes for Efficient CO2 Separation

A series of phenolphthalein-based polyimide membranes with kinked spirobisindane and sterically bulky durene diamine (DDA) moieties were synthesized and then cross-linked via controlled thermal heating. The gas permeability and diffusivity of the copolymer membranes increased with an increasing DDA content, and the thermally treated cross-linked membranes showed further enhancements in these parameters. The cross-linked membrane with a DDA loading of 75 mol % exhibited a CO2 permeability of 1366.3 Barrer and CO2/N2 and CO2/CH4 selectivities of 20 and 14.5, respectively, approaching the 2008 Robeson upper bound and surpassing the separation performance of most phenolphthalein-based polyimide polymers. Furthermore, this membrane demonstrated strong resistance to physical aging up to 41 days and displayed stability against plasticization up to 20 atm.