Structure-Property Relationships of Post Sulfonated Poly(arylene ether sulfone) Membranes for Water Desalination

Clean water is critical to the safety, security and survivability of humankind. Nearly 41% of the Earth’s population lives in water-stressed areas, and water scarcity will be exacerbated by an increasing population. Over 96% of the total water is saline and only 0.8% is accessible fresh water. Thus, saltwater desalination has emerged as the key to tackle the problem of water scarcity. Our current work is aimed at two membrane processes for desalination – Electrodialysis and Reverse Osmosis. Sulfonated polysulfones are a potential alternative to state of the art thin film polyamides. Synthesized by step growth polymerization, polysulfone membranes have smooth surfaces and they are more chemically resistant relative to polyamides.

Research in our group suggests that monosulfonated polysulfone membranes have better transport properties than disulfonated polysulfone membranes. Post sulfonation of poly(arylene ether sulfone) is an effective way to strategically place the sulfonate ions along the backbone of the polymer chain. Rose and coworkers reported the controlled post-sulfonation of poly(arylene ether sulfones) that contained hydroquinone moieties.¹ The sulfonation reaction proceeded only at the hydroquinone units because all of the other rings were deactivated toward electrophilic aromatic sulfonation by the electron withdrawing sulfone groups.

Novel hydroquinone based, amine terminated oligomers were synthesized with block molecular weights of 5000 and 10,000 g/mol. They were post-sulfonated under controlled conditions, then crosslinked at their termini with epoxy reagents. Linear polymers containing monosulfonation were also synthesized using post sulfonation. The monosulfonated membranes depicted transport properties better than previously synthesized polymers with disulfonated and pre-sulfonated monomers. The membranes were also analyzed for hydrated mechanical properties.

References:

[1] Rose, J. B. Sulfonated polyarylethersulphone copolymers. EP8894A1, 1980.