Physical Aging, Plasticization and Their Effects on Gas Permeation in “Rigid” Polymers of Intrinsic Microporosity

• Published in: Macromolecules Vol. 48; no. 18; pp. 6553 - 6561
• Main Authors: Swaidan, Raja, Ghanem, Bader, Litwiller, Eric, Pinnau, Ingo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22.09.2015
• Subjects: hydrogen; methane; oxygen; permeability; polymers
• ISSN: 0024-9297; 1520-5835; 1520-5835
• DOI: 10.1021/acs.macromol.5b01581

Long-term physical aging and plasticization, two mobility-based phenomena that are counterintuitive in the context of “rigid” polymers of intrinsic microporosity (PIMs), were evaluated using pure- and mixed-gas permeation data for representative ladder and semiladder PIMs. PIMs between 1 and 4 years old retained from 10- to 1000-fold higher H2 and O2 permeabilities than commercial membrane materials with similar or higher selectivities. A triptycene-based ladder polymer (TPIM-1) exhibited very large selectivity gains outweighing permeability losses after 780 days, resulting in unprecedented performance for O2/N2 (P­(O2) = 61 Barrer, α­(O2/N2) = 8.6) and H2/N2 (P­(H2) = 1105 Barrer, α­(H2/N2) = 156) separations. Interestingly, TPIM-1 aged more and faster than its more flexible counterpart, PIM-1, which exhibited P­(O2) = 317 Barrer and α­(O2/N2) = 5.0 at 1380 days. Additionally, the more “rigid” TPIM-1 plasticized more significantly than PIM-1 (i.e., TPIM-1 endured ∼93% increases in mixed-gas CH4 permeability over pure-gas values compared to ∼60% for PIM-1). A flexible 9,10-bridgehead (i.e., TPIM-2) mitigated the enhancements induced by physical aging but reduced plasticization. Importantly, intra-chain rigidity alone, without consideration of chain architecture and ultra-microporosity, is insufficient for designing aging- and plasticization-resistant gas separation membranes with high permeability and high selectivity