Novel crosslinked brominated polyphenylene oxide composite nanofiltration membranes with organic solvent permeability and swelling property

：Organic solvent nanofiltration (OSN) membranes have gained increasing attention for their wide applications in organic phase system. However, the fabrication method rather than the swelling behavior receives more attention during the OSN testing. In this work, a thin-film composite membrane with an internal cross-linking network by reacting 4,4-bipyridine with brominated poly (2,6-dimethyl-1, 4-phenylene oxide) (BPPO) has been prepared for organic solvent nanofiltration (OSN). The bipyridine groups substituted on the polyphenylene oxide polymer backbone act as cross-linkers and cationic channels for remarkable chemical stability and high solvent permeability. The permeability of the cross-linked BPPO (CBPPO) thin-film membranes exhibited high related to the viscosity and solubility parameter of solvents. The stability of CBPPO membrane was studied via various organic solvent immersing experiments. The result demonstrated that the composite membrane swelling changed to an extent of no more than 2.01%. It can be attributed to the low conformational flexibility of polymer chains with a high crosslinking degree. The ethanol permeation and dye rejection were compared before and after soaking. The calculation of the MWCO and membrane potential of modified CBPPO membranes showed that the swelling behavior of the CBPPO composite membranes is mainly affected by the membrane charge densities rather than the pore size.