| As a membrane material used in plasmapheresis, polysulfone (Psf) has advantages in aspects of biocompatibility, chemostability, mechanical strength, which make it popular in the field of biomedical materials. But the hydrophobicity of PS would cause serious fouling during the process of plasmapheresis, resulting in the irreversible adsorption of proteins on Psf membranes, and reducing their permeablility at least 30%. Once the conformation of the absorbed proteins changed, severe injuries would take place, such as blood coagulation and activation of immunosystem. In order to prevent the fouling of proteins, most efforts of current researches are focused on hydrophilic modification of membrane surfaces. Through the hydrophilic modification, researchers expect to obtain biocompatible surfaces and maintain the intrinsic bulk properties of the material. Among these researches, physisorption and covalent attachment of poly(ethylene glycol) on surface of various materials has long been studied widely and there're a lot of papers and patents being published in past three decades. In 1990's, it was found that the capability of mono-layered PEG brush to resist protein fouling was much greater than that of multi-layered PEG. To our knowledge, forming a brush-like PEG inside the Psf hollow-fiber of ultrafiltration membrane has not been reported yet. In this paper, spin coated Psf films and hot compressed Psf sheets were used as the material to besurface-modified by grafting brush-like PEG with 4-azidobenzoic acid photocoupler. Achievement of simultaneous or sequential UV irradiation graft of MPEG on polysulfone sheets (or films) may provide the foundation for further advancement in tethering brush-like PEG on ultrafiltration Psf hollow fiberBy using pyridine as catalyst, MPEG-OTs was synthesized from MPEG and 4- tolylsulfonyl chloride with proper amount of pyridine/MPEG (7.5/1, wt/wt) in a tree neck flask under N2 atmosphere for 12 hrs. According to Gabriel's method, MPEG-NH2 was synthesized from MPEG-OTs and potassium phthalimide, and purified by means of recrystallization in dichloromethane//ether mixture at least three times until crystal pure product obtained.On the otherhand, 4-azidobenzoic acid (AzBA) which was prepared by the addition of sodium azide to the acidic diazonium chloride from 4-aminobenzoic acid was purified in ethanol water solution (ethanol: H2O= 6(v): 4(v)), and got 77% yield, crystal pure. Furthermore, AzBA was reacted with previously synthesized MPEG-NH2, forming 4-azidobenzoylimino-monomethoxy-poly(ethylene glycol) (ABIMPEG), using EDC as the coupler. For improvement of the activity photosensitizer, ABIMPEG was purified by reprecipitation in dichloromethane/ether mixture twice under blackout condition, and thoroughly vacuum dried. ABIMPEG has been identified by infrared, nuclear magnetic resonance and ultraviolet spectroscopis. Finally, MPEG-Na was grafted directly onto the surface of Psf sheets by "grafting to process" under the following conditions: (1) in the darkroom, adjust the concentration of ABIMPEG to 3mg/cm2, (2) incubated under N2 atmosphere for 5 hrs at 40C, (3) keep Psf films wet during UV irradiation for 50min.From water contact angle and protein absorption measurements, there was a great improvement of hydrophilicity and protein antifouling property of the Psf sheets (or films) grafted with MPEG. In sequential pathway, AzBA was first immobilized on the surface of Psf sheets (or films) under UV irradiation, then MPEG-NH2 through its amino group reacted with the -COOH of AzBA forming amide bond and grafted on. Efficiency of graft through simultaneous and sequential pathways by X-ray photoelectron spectroscopy was 20.8%, and 10.2% respectively.With atomic force microscope (AFM), obvious differences in the shape and the relative moduli were found between surfaces of MPEG grafted PS membrane through these two pathways. Evidences inferred that simultaneous pathway would produce a branched PEG brush on the surface, while sequential pathway was coupled with a monolayered...
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