Synthesis Of Amphilphilic Acrylonitrile-based Graft Copolymers For Polycrylonitrile Membrane Preparation

Amphiphilic graft or comb-like copolymers are promising surface-segregating additives for the development of antifouling membranes by nonsolvent induced phase separation process. The synthesis of new amphiphilic comb-like copolymers is important for the development of advanced membranes. In this thesis, we describe a facile method for the synthesis of an amphiphilic graft copolymer with polyacrylonitrile (PAN) as backbone and poly(2-hydroxyethyl methacrylate)(PHEMA) as side chains, which were used as an additive for fabrication of antifouling PAN membranes.Atom transfer radical polymerization (ATRP) of HEMA was carried out with poly(acrylonitrile-co-p-chloromethyl styrene)(PAN-co-PCMS, PANC) as macro initiator in the presence of CuCl/2,2’-bipyridine at50℃in dimethyl sulfoxide. The ATRP results in an amphiphilic graft copolymer poly[acrylonitrile-co(p-chloromethyl styrene-g-2-hydroxyethyl methacrylate)](PAN-co-(PCMS-g-PHEMA), PANCHEMA). Both the macroinitiators and graft copolymers were characterized by FT-IR,1H NMR, and GPC. Kinetics of the graft polymerization was also investigated, which indicates that the synthesis of PANCHEMA can be relatively controlled when CMS unit in the macro initiator is around5mol%.We prepared dense films of PANC and PANCHEMA by spin coating. The surface morphology and wettability of the copolymer films were studied by AFM and water contact angle measurement, respectively. It is demonstrated that phase segregation between the backbones and the side chains of PANCHEMA takes place, and the surface hydrophilicity increases with the length of the PHEMA side chains.A series of PAN membranes were prepared by nonsolvent induced phase separation process using PANCHEMA as additive. The membranes were characterized by XPS, FT-IR/ATR, SEM and water contact angle measurement. Filtration experiments of pure water and bovine serum albumin (BSA) solution were carried out. SEM images show that the blend membranes have a typical asymmetric structure similar with PAN membrane, besides many honeycomb-like holes appeared in the membrane bulk. XPS and FT-IR/ATR data reveal that surface segregation of PANCHEMA occurs at the surface of the blend PAN membrane, which can be increased by annealing treatment. It is also demonstrated that the addition of PANCHEMA can improve the hydrophilicity of PAN membrane as well as the antifouling properties.