Molecular Design of Hydrophilized Polyethersulfone to Enhance Water/Salt Selectivity

Abstract

Understanding the relationship between the polymer chain structure and its water and salt transport structure–property is crucial for the development of hydrophilized polyethersulfone materials as candidates for high-performance desalination membranes. A series of novel hydrophilic polyethersulfone (HPES) copolymers were designed. Three hydrophilic molecules, thioglycolic acid, dl-cysteine hydrochloride, and 2-(dimethylamino) ethanethiol hydrochloride, were selected to modify allyl-containing polyethersulfone via thiol–ene click chemistry to prepare HPES-TGA, HPES-CYSAH, and HPES-DMAET with a controllable content of carboxyl, cysteine, and amino groups. Compared with the commercial sulfonated polysulfone (SPSF), the novel HPES polymers, especially HPES-CYSAH membranes, showed the best ideal desalting properties. The transport property measurements and simulation results show that HPES-CYSAH has the highest free volume fraction (FFV) and the strongest hydration capacity, which was also confirmed by the simulated state of the polymer in brine. This study suggests that the incorporation of bulky hydrophilic groups onto poly(arylene ether sulfone) backbone, especially zwitterionic groups, is expected to be an effective strategy for the preparation of chemically robust desalination membrane with high water permeability and high water/salt selectivity.