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. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1924-1934