Transport properties of small molecules in zwitterionic polymers

Despite great interests in using zwitterionic polymers for membrane surface modification to enhance antifouling properties, there lacks fundamental understanding of the relationship between polymer structure and water/salt separation properties. In this study, two series of zwitterionic polymers were prepared from sulfobetaine methacrylate and 2-methacryloyloxyethyl phosphorylcholine. Both are crosslinked by poly(ethylene glycol) diacrylate (PEGDA). These copolymers were thoroughly characterized in terms of sol-gel fraction, density, glass transition temperature, contact angle, water and salt transport properties, and pure-gas permeability. Interestingly, the zwitterionic polymers exhibit water sorption and permeability similar to noncharged poly(ethylene glycol)-based materials. These zwitterionic polymers exhibit lower NaCl diffusivity and permeability and thus higher water/NaCl selectivity than the non-charged PEG-based materials at similar water volume fractions, demonstrating their promise for membrane surface modification for desalination and wastewater treatment.