Exploration of antifouling zwitterionic polyimide ultrafiltration membrane based on novel aromatic diamine monomer

In this study, a new kind of aromatic diamine monomer named as 1,4-bis(4-aminophenyl)piperazine (BANPZ) was particularly designed and synthesized, and then the novel zwitterionic polyimide (ZPI) was prepared through a two-step process including polycondensation and quaternary amination reaction. The chemical structures of the prepared monomer and polymers were identified by FTIR and 1H NMR measurements, respectively. Meanwhile, the inherent viscosities, molecular weights, solubility behaviors and thermal properties of two obtained polymers were thoroughly characterized. Compared with the control polyimide (PI) membrane, the presence of zwitterionic groups considerably improve the hydrophilicity of the ZPI membrane, thereby enhancing the water permeability to some extent without obviously affecting the rejection ratio. Based on the static protein adsorption and dynamic cycle ultrafiltration experiments, the ZPI membrane exhibited persistent antifouling property, which was demonstrated by the flux decline ratio and filtration resistance. In particular, the water flux recovery ratio of the ZPI membrane was retained at 96.0% after a three-cycles of BSA solution filtration, which was much higher than that of the PI membrane (76.7%), suggesting excellent long-term performance stability. This new approach provided a valuable strategy of combining polymer chemical structure optimization and mature non-solvent induced phase separation (NIPS) method, which could greatly drive the development and application range of separation membranes.