Vinyl-Addition Fluoroalkoxysilyl-Substituted Polynorbornene Membranes for CO2/CH4 Separation

Natural gas production and utilization have grown tremendously in recent decades, which highlights the need for improved, high-throughput purification methods. In the field of polymeric membrane-based gas separations, a detailed understanding of molecular structure–property relationships are critical to overcoming the permeability–selectivity trade-off. Prior work has highlighted that alkoxysilyl-substituted vinyl-addition polynorbornenes (VAPNBs) are promising candidates for natural gas purification, having exceptional H 2 S/CH 4 and modest CO 2 /CH 4 permselectivity. To improve their CO 2 /CH 4 separation performance, we herein describe a series of fluoroalkoxysilyl-substituted VAPNBs. We demonstrate that the incorporation of fluoroalkoxysilyl substituents yields a series of polymeric materials whose CO 2 /CH 4 permselectivity increases as a function of fluorine incorporation. Interestingly, these enhanced selectivity characteristics are realized with minimal decreases to overall CO 2 permeability. While it was initially hypothesized that introduction of fluorinated units would decrease CH 4 solubility, detailed sorption analysis revealed that the observed increases in CO 2 /CH 4 permselectivity were due almost exclusively to enhanced CO 2 sorption in fluorine-containing VAPNBs. Computational studies provided insights into the electronic interaction energies between gas molecules and polymer repeat units across the nonfluorinated and fluorinated series, respectively.