(538g) Highly Selective Canal Ladder Polymers for Gas Separations: Tuning Backbone Conformation and Alkyl Functionalities

The development of materials with improved transport properties is necessary to further enable membrane technologies for emerging industrial applications. In this work, a new family of polymers based on Catalytic Arene-Norbornene Annulation (CANAL)^[1] polymerization is discussed for its application as gas separation membranes. CANALs are rigid ladder polymers similar in structure to PIMs. However, from a design standpoint PIMs contain Tröger’s base-^[2] or dioxane-based^[3] connectivity, while CANALs feature norbornyl benzocyclobutene backbones, thereby introducing a new high-performing ladder architecture to the gas separation field.

We have investigated how subtle changes in short alkyl substituents have an impact on transport properties.^[4] The unique nonpolar, rigid backbone of CANALs that feature no heteroatoms, make them an exceptional model system for fundamental investigations of the structure-property relationships of ladder polymers. An analysis of the energetic contributions to sorption and diffusion interestingly showed that CANALs present features of both dense and microporous polymers.

Recent developments allowed the formation of a new high molecular weight CANAL polymer featuring five-membered rings in the polymer backbone. By making this modification on the backbone conformation, we have been able to achieve remarkable combinations of high selectivity and permeability. In particular, H₂/CH₄, H₂/N₂, and O₂/N₂ separations showed performance beyond the 2015 upper bounds^[5], as well as 2008 H₂/CO₂ and CO₂/CH₄ upper bounds. Mixed-gas data were also performed for a broad range of compositions and pressures to assess the potential of this new material in more realistic conditions, and compared with pure- and mixed-gas upper bounds^[6], showing very promising results. Sorption and diffusion experiments, as well as X-ray scattering, were analyzed to provide a fundamental understanding of the exceptional performance reported.

The structural diversity explored in this work, and the remarkable results obtained, can provide a rational to design new microporous polymers with enhanced transport properties. Thereby, CANALs represent a new platform of materials with potential to address fundamental limitations in current design strategies for polymer membranes.

References

[1] S. Liu, Z. Jin, Y. C. Teo, Y. Xia, J. Am. Chem. Soc. 2014, 136, 17434.

[2] M. Carta, R. Malpass-Evans, M. Croad, Y. Rogan, J. C. Jansen, P. Bernardo, F. Bazzarelli, N. B. McKeown, Science (80-. ). 2013, 339, 303.

[3] P. M. Budd, E. S. Elabas, B. S. Ghanem, S. Makhseed, N. B. McKeown, K. J. Msayib, C. E. Tattershall, D. Wang, Adv. Mater. 2004, 16, 456.

[4] H. W. H. Lai, F. M. Benedetti, Z. Jin, Y. C. Teo, A. X. Wu, M. G. De Angelis, Z. P. Smith, Y. Xia, Macromolecules 2019, 52, 6294.

[5] R. Swaidan, B. Ghanem, I. Pinnau, ACS Macro Lett. 2015, 4, 947.

[6] Y. Wang, X. Ma, B. S. Ghanem, F. Alghunaimi, I. Pinnau, Y. Han, Mater. Today Nano 2018, 3, 69.