(3ef) Poly(ionic liquid) Block Copolymers for CO2 Capture

Ionic liquids possess low vapor pressures, high ionic conductivities, wide electrochemical stability ranges, broad thermal stabilities, and tunable solubilities enabling their use in a wide suite of devices such as lithium batteries, fuel cells, solar cells, light emitting diodes, and gas separation membranes.^[1]  Attempts to synthesis improved materials by polymerizing ionic liquid molecules have however produced mixed results.  For example, in gas separation membranes a trade off exists between the mechanical integrity gained by polymerizing an ionic liquid and the permeability that is lost in the process.^[2]  Fortunately, phase separated polymer membranes formed by diblock copolymers may offer a suitable comprise between mechanical integrity and desired properties for all of the applications listed above.  Already membranes formed from conventional diblock copolymers with poor CO₂ solubility have have shown improved separation results for CO₂/N₂ and CH₄/N₂ separations, with the increases in selectivity attributed to the orientation of cylindrical block orthogonal to the surface.¹

At NETL I have developed techniques for preparing diblock copolymers incorporating monomers with improved CO₂ solubility, such as ionic liquids, using a combination controlled radical polymerization techniques and click chemistry. ^[3]  The core synthesis centers on the polymerization of c-vinyl triazole monomers^[4] using free radical and reversible addition-fragmentation chain-transfer (RAFT) polymerizations.^[5]  Quaternization with amines, followed by ion-exchange reactions with LiTf₂N produces a poly(ionic liquid).  Approaches for producing block copolymers from these pILs will be discussed, as will strategies for synthesizing, and subsequently crosslinking block copolymers to form membranes.  Alternative approaches such as directly polymerizing of c-vinyl triazolium salts, and the incorporation of ionic liquid groups unto polymer backbones using the thiol–ene reaction will also be discussed.

This experience, combined with expertise using photo and click chemistry gained during my Ph. D. will support my goal as an assistant professor of starting a research group focusing on the development of materials with improved properties for a myriad of end applications.

[1]        D. Mecerreyes, Prog. Poly. Sci. 2011, 36, 1629.

[2]        J. E. Bara, D. E. Camper, D. L. Gin, R. D. Noble, Acc. Chem. Res. 2009, 43, 152.

[3]        H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. Int. Edit. 2001, 40, 2004.

[4]        H. Nulwala, K. Takizawa, A. Odukale, A. Khan, R. J. Thibault, B. R. Taft, B. H. Lipshutz, C. J. Hawker, Macromolecules 2009, 42, 6068.

[5]        G. Moad, E. Rizzardo, S. H. Thang, Aust. J. Chem. 2005, 58, 379.