Synthesis Of PVDF-Based Amphiphilic Copolymers And Their Modification Effects For PVDF Micro/Ultrafiltration Membrane

PVDF is one of the most popular materials for micro filtration (MF) and ultrafiltration (MF) membranes because of its excellent mechanical properties, thermal and chemical stability. Despite its advantages as membrane material, the hydrophobic character of PVDF often leads to a serious flux loss in water phase filtration due to membrane fouling. Besides, the poor hemo-compatibility of PVDF membrane also limits its application in biomedical field. A commonly-used approach to solve this problem is the hydrophilic modification of PVDF membranes. Blending with amphiphilic additives has been proven to be a facile and efficient method to prepare hydrophilic UF/MF membranes. When an amphiphilic copolymer is blended with the hydrophobic membrane materials and prepared a blend membrane via immersion-precipitation process, the amphiphilic copolymer can preferentially segregate to the surfaces of blend membranes, and improve the hydrophilicity of blend membranes. In this thesis, we synthesized a series of amphiphilic copolymers with different chemical composition, and used them as additives to prepare hydrophilic and anti-fouling PVDF membranes.Amphiphilic graft copolymers having PVDF backbones and poly(N-isopropylacrylamide) (PNIPAAM) or poly(acrylic acid) (PAA) side chains were synthesized viaγ-ray pre-irradiation induced graft polymerization in water phase suspension. The synthesized PVDF-g-PNIPAAM, PVDF-g-PAA copolymers were used as additives in the preparation of PVDF porous membranes by immersion precipitation. The surface chemical compositions of the prepared blend membranes were analyzed using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found the amphiphilic copolymers had been segregated to the surface of membranes. Scanning electron microscopy (SEM) observation had found that both copolymers have good pore-forming ability. The membrane hydrophilicity was evaluated by water contact angle measurement, and it was found that the hydrophilicity of blend membranes had been greatly improved.PVDF-based zwitterionic graft copolymers were synthesized through copolymerization of y-ray pre-irradiated PVDF powder with N,N-dimethylaminoethyl methacrylate(DMAEMA) in water suspension followed by quaternization reactions. The synthesized zwitterionic copolymers were used as additives to prepare microfiltration membranes by non-solvent induced phase separation method. The surface compositions, water contact angle, water permeation, protein-resistant and separation property were evaluated in detail. It was found that modified membranes had significantly improved hydrophilicity and stronger protein resistance in comparison to the control PVDF membrane. The modifying effects of different zwitterionic copolymers were compared in detail. Membranes modified by PVDF-g-SBMA and PVDF-g-CBMA-2 have better hydrophilicity and stronger protein resistance than membrane modified by PVDF-g-CBMA-3, which is due to the better hydrogen bridging effect of SBMA and CBMA-2.Amphiphilic precursor PVDF-g-PDMAEMA was synthesized via ATRP method and blended with PVDF to prepare porpous membranes, the 3-bromopropionic and 1,3-propane sultone were used as quaternization agent to transit the PDMAEMA into poly(zwitterionic) by surface reaction of membranes. The kinetics of the reaction was investigated by determining the gained weight of membranes, and found that 1, 3-propane sultone was more reactive than the 3-bromopropionic in the zwitterioniclization reactions. The XPS results confirmed that nearly 75% of PDMAEMA had been quaternized in 48h reaction by 1,3-propane sultone, while only 62% conversion was gained by 3-bromopropionic. Patelets adhesion results had implied that the modified membranes have better biocompatibility than PVDF-g-PDMAEMA/PVDF blend membranes.