Semi-interpenetrating polymer networks for efficient carbon molecular sieve gas separation membrane

Carbon molecular sieve (CMS) membranes represent a class of high-performance separation materials capable of surpassing the conventional permeability-selectivity trade-off. Introducing fillers into polymer precursors can further enhance the performance of the resulting CMS membranes; however, incompatibility between fillers and the polymer matrix often results in interfacial defects. In this study, the small-molecule cross-linker N,N ′-1,3-phenylenedimaleimide (PDM) was incorporated into a 6FDA-BPDA/TFDB polyimide to prepare optically transparent, uniform, and defect-free PDM-x precursor membranes. These precursor membranes were first subjected to thermal treatment at 300 °C for 1 h to form a semi-interpenetrating polymer network (SIPN) structure, and then pyrolyzed at 550 °C to obtain PDM-x-SIPN CMS membranes. The successful formation of a cross-linked semi-interpenetrating polymer network (SIPN) in the precursor was verified by TGA, ATR-FTIR, and XRD analyses. The resulting PDM-20-SIPN CMS membrane delivered exceptional gas-separation performance, with O 2 and CO 2 permeabilities of 1631 and 9904 Barrer, and O 2 /N 2 and CO 2 /CH 4 selectivities of 6.7 and 67.8, respectively—exceeding the latest upper-bound limits. Furthermore, the membrane showcased outstanding aging resistance over 720 h, significantly outperforming the conventional 6FDA-BPDA/TFDB CMS membrane. This study not only offers a robust precursor-design strategy, but also provides a foundation for the future development of high-performance CMS materials in sustainable separation processes.