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Elimination of CO₂/N₂ Langmuir Sorption and Promotion of “N₂-Phobicity” within High-Tg Glassy Membranes
- Maroon, Christopher R., Townsend, Jacob, Gmernicki, Kevin R., Harrigan, Daniel J., Sundell, Benjamin J., Lawrence, John A., Mahurin, Shannon M., Vogiatzis, Konstantinos D., Long, Brian K.
- Macromolecules 2019 v.52 no.4 pp. 1589-1600
- carbon dioxide, models, nitrogen, permeability, solubility, sorption
- We demonstrate that the CO₂/N₂ gas separation performance of alkoxysilyl-substituted vinyl-added polynorbornenes (VAPNBs) may be significantly enhanced via incorporation of the monomer 5-tris(2-methoxyethoxy)silyl-2-norbornene. As the molar ratio of this monomer is increased, substantial increases in CO₂/N₂ selectivity are realized with minimal decrease in CO₂ permeability. This trend ignores the traditional permeability/selectivity “trade-off” relationship and yields an optimal membrane whose performance reaches the 2008 upper bound for CO₂/N₂ separations. Though the inclusion of 5-tris(2-methoxyethoxy)-silyl-2-norbornene units was initially hypothesized to maximize CO₂ solubility, detailed gas sorption studies reveal that these highly glassy materials essentially lack any Langmuir sorption component and indicate that their improved CO₂/N₂ selectivity is due to decreased N₂ solubility within the matrix. Computational modeling suggests that the source of this apparent “N₂-phobicity” is likely explained through comparative analyses of polymer–polymer and polymer–gas interactions. Lastly, mixed-gas permeation tests are performed to provide a more realistic look at real-world gas separation performance.