Zwitterionic PMMA-r-PEGMA-r-PSBMA copolymers for the formation of anti-biofouling bicontinuous membranes by the VIPS process

Zwitterionic modifications have been widely investigated to endow surfaces of membranes with fouling resistance. However, the approaches reported are mostly surface modifications, making the membrane preparation lengthy and difficult to scale-up. Ideally, zwitterionization should be achieved during membrane formation, but compatibility issues frequently arise between the zwitterionic material, hydrophilic, and the matrix polymer, hydrophobic. Here, a poly(methyl methacrylate-co-ethylene glycol methacrylate-co-sulfobetaine methacrylate) (PMMA-r-PEGMA-r-PSBMA) copolymer is introduced to form zwitterionic poly(vinylidene fluoride) (PVDF) membranes. The MMA segments are used to form hydrophobic interactions with PVDF, while PEGMA units and SBMA units are employed as solubility-enhancing groups and antifouling groups, respectively. After forming the membranes by the vapor-induced phase separation, followed by their complete characterization (SEM, AFM, FTIR, mapping FT-IR, WCA, etc.), it is shown that PMMA-r-PEGMA-r-PSBMA reduces membrane biofouling by about 90% from a large span of biofoulants (Escherichia coli, fibrinogen, BSA, proteins from plasma, blood cells), which validates the design of the copolymer and the in-situ modification. Fouling in a dynamic environment was also tested via BSA filtration and water permeability after PPP incubation. The total flux recovery ratio of the zwitterionic blended membranes were higher (around 55%) compared to a commercial hydrophilic PVDF membrane (around 12% for BSA filtration and 35% for water permeation). The range of application of these zwitterionic bi-continuous microfiltration membranes is wide, going from wastewater-treatment to biomedical-related applications.