Narrow-Pore-Size-Distribution PSf-g-DVB Membrane towards Purification of Low-Molecular-Weight Dextran

The safety and efficacy of low molecular weight dextran (LMWD) in pharmaceutical applications critically depend on the uniformity of its molecular weight distribution. In this study, a novel ultrafiltration (UF) modified membrane was prepared by UV-induced surface graft polymerization on the commercial polysulfone (PSf) membrane for the efficient separation of LMWD. Benzophenone (BP) was employed as the photoinitiator to initiate the grafting polymerization of the difunctional monomer divinylbenzene (DVB). During the polymerization process, DVB underwent both chain homopolymerization and intermolecular crosslinking, forming a dense three-dimensional network that significantly reduced the membrane pore size and enhanced its separation selectivity. The optimized PSf-g-DVB membrane, prepared with a concentration of 2 wt% DVB and 1 wt% BP, achieved over 85% rejection of 20 kDa dextran, while the rejection rate for 2 kDa dextran was only 0.2%, with a water permeance of 5.4 L·m -2 ·h -1 ·bar -1 . Furthermore, the membrane demonstrated excellent stability, maintaining a rejection difference of 70% between the two different molecular weights of dextrans after 48 hours of continuous filtration. In filtration experiments with mixed dextran solutions, the PSf-g-DVB membrane exhibited a separation factor as high as 11.5, nearly 9 times higher than that of the commercial PSf membrane, further confirming the feasibility of UV-grafted membrane modification for the selective sieving of LMWD, and offering a green and effective approach for pharmaceutical-grade dextran purification.