Poly(Acrylonitrile-co-maleic Acid): Membrane Fabrication And Surface Modification

The main objectives of this thesis are to synthesize a novel functional copolymer of poly(acrylonitrile-co-maleic acid) (PANCMA) as a membrane material, to investigate the thermodynamics and kinetics of liquid-liquid phase separation behavior of PANCMA dope, to fabricate PANCMA hollow fiber membrane, and to modify the membrane surface by the immobilization of poly(ethylene glycol)s and/or biomacromolecules.The copolymerization of acrylonitrile and maleic anhydride using 2,2'-azobisisobutyronitrile (AIBN) as initiator was studied in dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and dimethylacetamide (DMAc) respectively. It was found that the molecular weight of poly(acrylonitrile-co-maleic anhydride) is too low (Mr] < 10xl04 g/mol), and the content of maleic anhydride in PANCMA copolymer is also low (< 6 mol%). Thus, the resulting copolymers by the solution copolymerization are not suitable for membrane fabrication and surface modification.The copolymerization of acrylonitrile and maleic anhydride was conducted by water-phase precipitation copolymerization (WPPCP) method with potassium persulfate-sodium sulfite as initiator system and water as reaction medium. Effects of monomer ratio, initiator concentration, reaction time and addition frequency of AN on the copolymerization were explored. FT-IR, -NMR, element analysis and intrinsic viscosity measurement were used to characterize the PANCMAs. It was found that the molecular weight of PANCMA increases and varies from 10x104 to 40x104 g/mol. Moreover, the MA content in the PANCMA can be controlled through changing the reaction condition, which ranges from 0 to 15mol%. These results indicate that the PANCMAs synthesized by WPPCP are suitable for further membrane fabrication and surface modification.-3-Cloud point curves in phase diagram of the PANCMA/solvent/nonsolvent membrane-forming systems were determined by the combination of turbidity measurement and linearized cloud point relation (LCP) to investigate the phase separation behavior. The diffusion kinetics of solvent and nonsolvent were studied also. Then, the corresponding membrane structure and properties can be explained from these two aspects. It was found that the phase separation behavior of the PANCMA/solvent/nonsolvent systems with and without additive such as PVAL or PVP agrees with the LCP correlation. Therefore, the binodal lines were calculated according to the LCP correlation. For the PANCMA/DMSO/nonsolvent system, water with the lowest coagulation value shows the strongest coagulation power. The system at higher temperature becomes thermodynamically more stable, and raises the diffusion exchange rate of solvent and nonsolvent at the interface according to the diffusion kinetics. For the PANCMA/DMSO/(H20+DMSO) system, with the addition of DMSO to nonsolvent, the cloud point curves shifts to the polymer-nonsolvent axis, and the homogeneous phase region is broadened, system becomes thermodynamically more stable and needs more nonsolvent mixture to induce liquid-liquid phase separation. Additives have effects on both the thermodynamics and kinetics of the system, and the membrane structure and property will depend on the predominant factor.Based on the study of thermodynamics and kinetics of the membrane-forming systems, PANCMA hollow fiber membranes were fabricated by phase inversion method and some spinning parameters were investigated. The PANCMA dope solutions with high molecular weight or high concentration have a high viscosity, ?resulting in the decrease of pore size and pore number on the corresponding membrane surface. Accordingly, the water flux decreases and the bovine serum albumin (BSA) rejection increases for the PANCMA hollow fiber membrane. With the increase of casting solution temperature, a denser membrane structure can be formed, but the membrane surface varies little. When the total concentration of casting solution is constant, with the addition of additives such as PVP and PVAL, the-4-water flux of PANCMA hollow fiber membrane increases and its BSA rejectio...