Surface Zwittericalization And Properties Of Polysulfone Ultrafiltraion Membranes

Polysulfones are one of the most popular ultrafiltration/microfiltration (UF/MF) membrane materials, owing to their excellent chemical resistance, thermal stability, mechanical strength, as well as machinability. In fact, they have been widely applied in wastewater treatments, food and beverage purification, protein separation, hemodialysis, biomedical fields and so on. However, since the inherent hydrophobic characteristics of polysulfones, protein, bacteria, platelet and organics in the feed solution are prone to adsorb onto membrane surfaces and into pore walls, which may lead to membrane fouling, degenerate membrane property, and shorten operating life. In biomedical field, protein adsorption and platelet adhesion resulting from contact with hydrophobic membranes may lead to serious blood coagulation and immunologic rejection. Therefore, polysulfone membrane modification is necessary to meet many aspects of demand. With the purpose of overcoming the shortcoming of available modification methods, a series of reactive amphiphilic copolymers suitable for polysulfone membrane modification were prepared based on molecular design in the present thesis. In order to improve the hydrophilicity/water permeability, anti-fouling ability and hemocompatibility of polysulfone UF membrane, the zwitterionic polymers with strong hydration ability were incorporated into membrane surface via the combination of blending and membrane surface reaction.Firstly, the telechelic polysulfones with terminal hydroxyl groups were synthesized via condensation polymerization, then the amphiphilic copolymers polysulfone-block-poly(2-dimethylaminoethyl methacrylate) (PSF-b-PDMAEMA) and polyethersulfone-block-poly(2-dimethylaminoethyl methacrylate) (PES-b-PDMAEMA) were synthesized via atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT) polymerization, respectively. The synthesized amphiphilic copolymers were then blended with polysulfone resin to fabricate the blend membrane PSF/PSF-b-PDMAEMA or PES/PES-b-PDMAEMA by non-solvent induced phase separation (NIPS) process. The hydrophilic PDMAEMA chains in the copolymer additives spontaneously migrated toward the interfaces (including membrane surface and pore walls) during membrane formation process, the hydrophilicity and permeability of the blend membranes were greatly improved and the PDMAEMA chains rendered the membranes with "stimulation-responsive" property. Then the surface-enriched PDMAEMA chains were transformed into zwitterionic poly(carboxybetaine methacrylate) (PCBMA), zwitterionic poly(sulfobetaine methacrylate) (PSBMA) and cationic polymer by the quaternization with 3-bromopropionic acid (3-BPA), 1,3-propane sultone (1,3-PS) and 1-bromodecane, respectively. The zwitterionic membranes showed significantly improved antifouling ability and hemocompatibility. And the cationic membranes exhibited excellent antibacterial property.Based on the hydroxyl-terminated polyethersulfone, amphiphilic copolymer polyethersulfone-block-poly(2-hydroxyethyl methacrylate) (PES-b-PHEMA) was beforehand synthesized via RAFT polymerization, then used as the blending additive of PES blend membranes. The surface enriched PHEMA blocks on membrane surface acted as an anchor to immobilize the bromoalkyl initiator, the zwitterionic polymer poly(sulfobetaine methacrylate) (PSBMA) were subsequently grafted onto the PES blend membranes through surface-initiated atom transfer radical polymerization (SI-ATRP), and the grafting yield of PSBMA increased almost linearly as the polymerization time, which was in accordance with the living character. The surface chemistry and morphology of the modified PES membranes changed obviously, and the hydrophilicity of the modified membranes was greatly improved. The modified membranes were capable of separating proteins from protein solution and oil from oil/water emulsion efficiently, and remarkably weaken the irreversible fouling caused by protein or oil adsorption, thus the antifouling performance was significantly improved. The modified membranes exhibited good reversible electrolyte-responsive behavior. In addition, the incorporation of PSBMA suppressed the adhesion and activation of platelets, prolonged the plasma recalcification time, and endowed the modified membranes with excellent blood compatibility.PES/PES-b-PHEDMA blend membranes containing a reactive block copolymer PES-b-PHEDMA were firstly prepared by traditional NIPS process. The zwitterionic hydrogel thin films were then constructed from membrane surface via free radical cross-linking polymerization between SBMA and reactive ethylenic bonds in membrane surface, with poly(ethylene glycol) diacrylate (PEGDA) as cross-linker. Both the pore size and porositiy of the hydrogel-anchored PES membranes decreased, while BSA rejection increased, thus the separation efficiency of PES membrane was effectively enhanced. Due to the strong water binding capacity of zwitterionic hydrogel, the hydrogel-modified PES membranes showed significantly improved hydrophilicity, water uptake, anti-fouling ability and hemocompatibility. More importantly, the hydrogel thin films showed good durability in long-term tests, because the chains were entangled between hydrophobic chains and PES matrix, and the zwitterionic hydrogel thin film was firmly anchored onto PES membrane via covalent bond.In order to improve the modification efficiency of amphiphilic copolymer and separation ability of polysulfone (PSF) membranes, polyethersulfone-block-poly (sulfobetaine methacrylate) (PES-b-PSBMA) block copolymer micelles (core-shell) were firstly prepared. Then PSF/PES-b-PSBMA composite membranes were fabricated via filtration and deposition of the PES-b-PSBMA micelles onto the PSF UF membrane surface. The analysis of attenuated total reflection-flourier transformed infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electronic microscopy (SEM) were applied to analyze the surface chemistry and morphology evolution of the fabricated membranes, which confirmed the successful deposition of zwitterionic copolymer micelles on the PSF membrane surface. The surface hydrophilicity of the PSF/PES-b-PSBMA composite membranes was improved, while the water flux was slightly decreased. The protein separation ability was remarkably enhanced, the rejection of BSA was improved from 42% to 96%, and the separation factor of BSA and lysozyme (LYZ) was increased from 1.8 to 29. The developed membranes have great potential in protein separation and purification, and this work provides us with an effective development of novel functional polymer membranes.In summary, surface zwittericalization of polysulfone UF membranes was successfully realized via the molecular design based on amphiphilic polysulfone copolymers and the combination of blending and post surface reaction. The anti fouling performance, hemocompatibility and separation properties of polysulfone UF membranes were remarkably improved, and the present work supplies us with some useful academic and technological information on the fabrication of polysulfone UF membranes with high performance.