(187a) The Development of Polymeric Membranes for Water, Gases and Fuel Cells

The speaker spent eight years at the Union Carbide Corporation, during which he contributed to the development of the poly(arylene ether) family, typified by the polysulfones (1).  This basic work has been continued in a controlled fashion for the last 37 years since he joined the faculty of Virginia Tech. In the early days we focused largely on the generation of engineering thermoplastics, both amorphous systems and semicrystalline materials, such as the poly(arylene ether ketones). With the beginning of our National Science Foundation Center on Structural Adhesives and Composites, we focused attention on the synthesis of especially amino terminal functional oligomers based upon materials now known as Udel and related systems.  The amino systems were prepared quantitatively and were demonstrated as early as the 1980s to be capable of significantly toughening the epoxy resin matrices used for carbon fiber and glass composites.  They were differentiated from their analogous blends by the fact that the chemical reactions developed a controlled morphology and chemical resistance, which led to very significant fracture-toughness improvements in crosslinked epoxies and carbon fiber composites.  Interactions with industrial organizations led to the commercialization of the materials, which are now present in toughened epoxies in both the Airbus and Boeing products (2). 

The last decade in this area has turned toward the development of membranes, first for fuels cells (3) and more recently for water (4) and gas separations (5). In the first two cases, sulfonated copolymers have been investigated, including linear, random, and multiblock systems, which in the salt form can be water purification membranes; whereas in the acid form they are leading candidates for both portable power and vehicle hydrogen/air systems.  Variations on these materials have led to crosslinkable systems, which have potential for further reduced swelling and enhanced selectivities for, as an example, seawater desalination.  The comparison of the earlier studied post-sulfonated systems with that prepared by a one-step directly sulfonated comonomer will be presented and the advantages of the latter will be emphasized.  Gas separation membranes also built upon earlier experience in high performance materials, such as polyimides, polyamideimides, and polybenzoxazoles.  Illustrations of these and typical properties will be provided.  Currently, further efforts are underway to generate water and gas separation membranes that contain both ionic and non-ionic covalently bound moieties to develop a controlled hydrophilicity needed. 

REFERENCES

1. A.G. Farnham, L.M. Robeson and J.E. McGrath, J. Appl. Polym. Sci., Symp. 26, 373 (1975).
2. Guo, R. and McGrath J.E. (2012). Aromatic Polyethers, Polyetherketones, Polysulfides, and Polysulfones. In: MatyjaszewskiK and Moller M. (eds.) Polymer Science: A Comprehensive Reference, Vol. 5, pp. 377-430. Amsterdam: Elsevier BV.
3. M.A. Hickner, H. Ghassemi, Y.S. Kim, B. Einsla and J.E. McGrath, “Alternative Polymer Systems for Proton Exchange Membranes,” Chemical Reviews (2004), 104(10), 4587-4611.
4. Water purification by membranes: The role of polymer science Geise, Geoffrey M.; Lee, Hae-Seung; Miller, Daniel J.; Freeman, Benny D.; McGrath, James E.; Paul, Donald R.   From Journal of Polymer Science, Part B: Polymer Physics (2010), 48(15), 1685-1718.
5. Effect of Free Volume on Water and Salt Transport Properties in Directly Copolymerized Disulfonated Poly(arylene ether sulfone) Random Copolymers. Xie, Wei; Ju, Hao; Geise, Geoffrey M.; Freeman, Benny D.; Mardel, James I.; Hill, Anita J.; McGrath, James E.  Macromolecules (2011), 44(11), 4428-4438.
6. Synthesis and Characterization of Multiblock Semi-crystalline Hydrophobic Poly(ether ether ketone) Hydrophilic Disulfonated Poly(arylene ether sulfone) Copolymers for Proton Exchange Membranes Yu Chen, Chang Hyun Lee, Jarrett R. Rowlett, and James E. McGrath, Polymer 53 (2012). Pp. 3143 – 3153.
7. Gas permeability, diffusivity, and free volume of thermally rearranged polymers based on 3,3’-dihydroxy-4,4’-diamino-biphenyl (HAB) and 2,2’-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). Sanders, David F.; Smith, Zachary P., Ribeiro, Claudio, P., Jr.; Guo, Ruilan, McGrath, James E.; Paul, Donald R.; Freeman, Benny D.  Journal of Membrane Science (2012), 409-410, 232-241.