Synthesis Of Amphiphilic Comb-shaped Block Copolymers And Application In Modification Of Membranes

Membrane processes are receiving increased attention for its high separate efficiency in modern times. However, a major obstacle to further application of membrane process is protein fouling during the operation. In order to solve this problem, the preparation and characteristics of anti-fouling membrane have be studied , and surfaces modification was one of the main methods. There is theirfore much interest in the modification of the surface to improve their hydrophilicity and antifouling. Amphiphilic comb-shape block copolymers with different structure parameters were synthesized by reversible addition- fragmentation transfer (RAFT) polymerization. Then polymers were used for the blend modification of PES ultrafiltration membrane and surface adsorption modification of PAN Films.The effection of the amphiphilic polymer structure on the membrane surface and capabilities were investigated in order to find the available method.Firstly, a series of amphiphilic comb-shape block copolymers, PSt-b-P(A-mPEG) and P(St-co-DMAM)-b-PDMAM-b-P(A-mPEG)] with different molecular masses of mPEG and polymer degree of mPEG, were synthesized successfully by addition-fragmentation transfer polymerization of styrene, N,N-dimethylacrylamide (DMAM) and poly(ethyleneglycol)methylether acrylate(A-mPEG) macromonomers.The copolymers were characterized by FTIR,1H-NMR spectroscopy and GPC. The results showed that these amphiphilic block copolymers synthesized by RAFT polymerization had high block efficiency and norrow molecular masses distribution. Secondly, these PSt-b-P(A-mPEG) copolymers were blended with PES to fabricate high surface-hydrophilic ultrafiltration membranes through a phase inversion process. Water contact angle, protein adsorption and ultrafiltration properties were determined for evaluating the antifouling property and hydrophilicity. It was found that the antifouling property of the blend membranes was considerably improved with negligible change of permeation properties, and the flux recovery ratio was remained high after BSA ultrafiltration. And the hydrophilicity of the membrane is increased by the increase of the content of the amphiphilic copolymer. The PEG-enriched surface exhibited higher hydrophilicity and the amount of protein adsorption was remarkably decreased from 6.8 to 0.5μg/cm2. The superior protein-adsorption-resistance rendered blend membranes more desirable recycling property. The flux recovery ratio was remained as high as 80.4% after three cycles of BSA ultrafiltration. Then, surface modification of polyacrylonitrile(PAN) surfaces was carried by using P(St-co-DMAM)-b-PDMAM-b-P(A-mPEG) by adsorption of the amphiphilic polymer at PAN surfaces from an aqeous solution. The accumulation of the amphiphilic polymers at the PAN surface was observed by XPS and contact angle measurements. The contact angle is decreased from 72.19 to 20.7. It showed that the hydrophilicity of the surface is improved after adsorption. Protein adsorption was measured under static conditions. The modified surfaces had generally lower adsorption of BSA than the unmodified PAN surfaces, the lowest amount of protein adsorption being 0.68μg/cm2.Lastly, the membrane was modified by chemical graft treatment by preadsorption of P(St-co-DMAM)-b-PDMAM firstly and then reacting with A-mPEG in the aqueous solution. FTIR spectra revealed that the PEG groups were introduced onto the surface of PAN membrane.The contact angle at the sueface of the modified membrane was reduced and the amount of protein adsorption is decreased availably. This showed that the hydrophilicity of the surface was improved efficiently.