Porous membranes modified by hyperbranched polymers II.: Effect of the arm length of amphiphilic hyperbranched-star polymers on the hydrophilicity and protein resistance of poly(vinylidene fluoride) membranes

Amphiphilic hyperbranched-star polymers (HPE-g  -MPEG) with different arm length were synthesized by grafting methoxy poly(ethylene glycol)s (MPEGs, M¯n=350,750 and 2000, respectively) to the hyperbranched polyester (HPE) molecule using terephthaloyl chloride (TPC) as the coupling agent, and blended with PVDF to fabricate porous membranes via phase inversion process. Membrane morphologies were observed by scanning electron microscopy (SEM) and atomic force microscope (AFM), and chemical composition changes of the membrane surfaces were measured by X-ray photoelectron spectroscopy (XPS). Water contact angle, static protein adsorption, and filtration experiments were used to evaluate the hydrophilicity and anti-fouling properties of the membranes. It was found that, with the increase in MPEG arm length, the MPEG segments of HPE-g-MPEG enriched at the membrane surfaces substantially, resulting in a significant decrease in water contact angle. Furthermore, the blend membranes containing longer arm HPE-g-MPEGs showed lower static protein adsorption, higher protein solution fluxes, and better protein solution flux recovery than the pure PVDF membrane.