(458a) Self-Assembling Random Zwitterionic Terpolymers As Novel Fouling- and Chlorine-Resistant Nanofiltration Membrane Selective Layers

Nanofiltration (NF) is widely used for removal of multivalent ions and larger small molecules from water, in applications that range from water softening to water and wastewater treatment. Currently, most commercial NF membranes feature cross-linked polyamide selective layers that are prone to fouling and highly sensitive to chlorine, a common disinfectant used to manage biofouling. Zwitterions, functional groups with equal numbers of positive and negative charges, strongly resist fouling. Previously, our group has developed high flux, fouling resistant, size-selective membranes utilizing the self-assembly of random zwitterionic amphiphilic copolymers (rZACs) to form a network of zwitterionic effective “nanochannels” that allow the permeation of water and smaller solutes. These membranes are exceptionally fouling resistant, showing little to no flux decline during the filtration of a wide range foulants and complete flux recovery with a water rinse. They have effective pore sizes around ~1.5 nm, and exhibit limited salt rejection. Here, we aim to expand the separation capabilities of zwitterion-containing copolymer selective layers to enhance charged solute rejection and impart anion selectivity. For this purpose, we synthesized a charged zwitterionic amphiphilic copolymer (CZAC) comprised of zwitterionic, hydrophobic, and carboxylic acid-containing repeat units: poly(trifluoroethyl methacrylyate-r-sulfobetaine methacrylate-r-methacrylic acid) (PTFEMA-r-SBMA-r-MAA). The presence of charged groups, through dissociated MAA repeat units segregated into the zwitterionic nanochannels, leads to selective rejection of salts and charged organic compounds. The salt rejection values and water permeances of these membranes are comparable with commercial NF membranes. Yet, unlike typical NF membranes, CZAC membranes are highly resistant to fouling and exposure to chlorine. Furthermore, the selectivity of the membrane can potentially be further tuned by the functionalization of carboxylic acid groups on MAA repeat units to access additional separations. These features demonstrate the promise and versatility of this new polymer family for a wide range of membrane applications.