(666b) Resilient Hollow Fiber Nanofiltration Membranes Fabricated from Crosslinkable Phase-Separated Copolymers

As membrane technologies become more critical to meeting the growing demand for energy efficient separations, a need has emerged for membrane platforms that can be tailored to accommodate the highly varied applications, feed compositions, and treatment demands of wastewater treatment, desalination, and pharmaceutical product purification. Nanofiltration (NF) membranes based on copolymer materials are a promising separations platform because they can be engineered at the molecular scale to address an array of process needs. Here, for example, a resilient NF membrane is developed through the molecular design of a poly(trifluoroethyl methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate-co-glycidyl methacrylate) [P(TFEMA-OEGMA-GMA)] copolymer that can be dip-coated onto hollow fiber supports. By exploiting the microphase separation of the oligomeric ethylene glycol side chains from the copolymer backbone and by elucidating the processing-structure-property relationships for the dip-coating process, membranes with pores 2 nm in diameter that exhibit a hydraulic permeability of 15.6 L m^-2 h^-1 bar^-1 were generated. The GMA repeat units were functionalized post-coating with hexamethylene diamine to incorporate positively-charged moieties along the pore walls. This post-coating functionalization yielded membranes that rejected 98% of the MgCl₂ from a 1 mM feed solution. Moreover, the reaction with the diamine-crosslinked the copolymer such that the membranes could operate stably in ethanol, an organic solvent that otherwise damaged the unreacted parent membranes. Finally, the chemical stability of the P(TFEMA-OEGMA-GMA) copolymer resulted in membranes that could operate continuously in aqueous solutions containing 500 ppm chlorine for a 24-hour period without exhibiting deterioration in the membrane nanostructure. These results demonstrate the ability to develop resilient, valence-selective NF membranes through the molecular engineering of the copolymer. The stability of these membranes has led to investigations of how they can withstand exposure to various organic solvents. By combining the versatility of molecularly designed copolymers with functionalities that can be utilized to increase the integrity of the membrane can further the use of membrane technologies into emerging applications.