Highly hydrophilic and low-protein-fouling polypropylene membrane prepared by surface modification with sulfobetaine-based zwitterionic polymer through a combined surface polymerization method

Poly(sulfobetaine methacrylate) [poly(SBMA)], a zwitterionic polymer, was successfully tethered in high density onto polypropylene (PP) membrane surface through a combined method consisting of UV-induced surface graft polymerization followed by surface-initiated atom transfer radical polymerization (ATRP). 2-Hydroxyethyl methacrylate (HEMA) was first immobilized onto PP membrane surface by UV-induced graft polymerization, and then each of the grafted poly(HEMA) chains, after coupled with 2-bromopropionyl groups, provided multiple initiation sites for subsequent ATRP of SBMA. Images from scanning electron microscope (SEM) showed that the membrane surface was fully covered with small dot-like surface structures of poly(SBMA) after 6 h of ATRP. Both attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR) and X-ray photoelectron spectroscopy (XPS) confirmed the grafted poly(HEMA) and poly(SBMA) on the membrane surface. Water contact angle measurements showed that the surface hydrophilicity of the PP membrane was improved significantly with the increase of the grafted poly(SBMA) content, and a water contact angle of as low as 17.4° was obtained in this study. Experimental results for protein solution filtration demonstrated that the extent of fouling was significantly reduced and most of the fouling on the modified PP membrane surface was reversible, suggesting good anti-protein-fouling performance.