Enhancing the hydrophilicity of polypropylene microporous membranes by the grafting of 2-hydroxyethyl methacrylate via a synergistic effect of photoinitiators

Membrane surfaces modified with polymers based on 2-hydroxyethyl methacrylate (HEMA) is promising for hydrophilicity, biocompatibility, and functionality. In this work, the UV-induced graft polymerization of HEMA onto polypropylene microporous membrane (PPMM) was studied using ferric chloride (FeCl3) and benzophenone (BP) as co-photoinitiators with different methods for the first time. It was found that the conventional photoinitiator, BP, could not initiate the grafting polymerization of HEMA on the PPMM. Incorporation of FeCl3 into the reaction system remarkably enhanced the grafting of HEMA onto PPMM, which could be ascribed to the “synergistic effect” between Fe3+ and BP. Results indicated that the maximum grafting degree for the soak method, which added monomer, photoinitiators and membranes in acetone/water mixture together was 2.5-fold greater than that for the adsorption method. Therefore, the grafting degree of HEMA on the membrane surface could be modulated in a wide range through the variation of UV irradiation time, monomer concentration, and BP/FeCl3 ratio. The poly(HEMA)-modified membrane surfaces were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Static water contact angle of the membrane surface indicated a decrease from 145° to 42° with the grafting degree increasing from 0 to 35.67 wt.%. Water drop lied on the modified surface with 35.67 wt.% of grafting degree permeated completely into the membrane pores in 3 s. Furthermore, these poly(HEMA)-tethered membranes showed well protein resistance and potential hemocompatibility due to the enhancement of surface hydrophilicity.