Synthesis Of Novel Fluorinated Block Copolymer And Research On Its Application In PVDF Membrane Field

PVDF possess outstanding properties such as mechanical strength,excellent chemical resistance,and thermal stability,which has been widely used in in seawater desalination,water treatment,chemical industry,and food.Now,challenges of PVDF membrane in the process of water treatment,in that it is hydrophobicity,low efficiency of separation,adsorption to proteins,and prone to membrane fouling.In view of the above problems,this paper starts with the design of the polymer structure of the membrane material,and block copolymers of PVDF were synthesized via iodinetransferpolymerization.Poly?vinylidene fluoride?-b-poly[2-?N,N-dimethylamino?ethyl methacrylate]?PVDF-b-PDMAEMA?,poly?vinylidene fluoride?-b-poly?nisopropylacrylamide??PVDF-b-PNIPAAm?,and Poly?vinylidene fluoride?-b-poly?1H,1H,2H,2H-perfluorooctyl ethyl acrylate?were synthesized,and the three kinds of PVDF-based block copolymers were applied to modification of PVDF separation membranes.Anovelsodiumbis[2-?2-1H,1H,7H-dodecafluoroheptyloxy?ethyl]-2-sulfosuccinate surfactant?FEOS*-6?with similar performance to ammonium perfluorooctanoate was synthesized,and application of iodine transfer polymerization of PVDF.The effects of different polymerization methods on the iodine transfer polymerization of PVDF were studied.The solution polymerization was suitable for the preparation of PVDF polymers with a low degree of polymerization,and the high polymerization degree of PVDF was obtained by method of emulsion polymerization.It was found that the easier the generation of the-CF₂CH₂I group in the higher the degree of polymerization of the macromolecular chain transfer agent,resulting in the inability to reversibly switch between active species and dormant species.The PVDF-based block copolymer of adding acrylic functional monomer was prepared by iodine transfer polymerization.The results of NMR spectra and GPC indicate that the block copolymer were successfully synthesized via iodine transfer polymerization.With the increase of the degree of polymerization of acrylic monomers,the crystallinity of PVDF in the block copolymer is restricted.To obtain polyvinylidene fluoride?PVDF?membranes with excellent antifouling properties,PVDF-b-PDMAEMA was blended into PVDF matrix to prepare modified membranes.With addition of block copolymers conspicuous improved the structure and performance of blend membranes,which resulted in a remarkable improvement of the hydrophilicity of the membrane.Compared with the pure PVDF membrane,the water flux of the resulting blend membranes was enhanced by 3 times,with the bovine serum albumin?BSA?rejection ratio maintained at a reasonable level??90%?.Also by incorporation of amphiphilic block copolymer,resistance to protein adsorption and high flux recovery ability of the blend membranes were achieved.The blend membranes with high BSA separation efficiency and excellent antifouling properties will find promising applications in the field of separation science specifically in sewage purification.Tunable pore diameter of membranes with sustainable antifouling performance was successfully fabricated.The membranes were composed of a commercial poly?vinylidene fluoride?blended with a PVDF-b-PNIPAAm block copolymer.The amphiphilic block copolymer,which was synthesized via iodine transfer polymerization,displays excellent miscibility with commercial PVDF.With addition of block copolymers conspicuous improved the structure and performance of blend membranes,which in turn enhance the hydrophilicity,amount of surface micropores,and pure water flux.As the same time,proper bovine serum albumin?BSA?rejection ratio was maintained.Block copolymer has a lower critical solution temperature?LCSTs?in the membrane that depends on PNIPAAm chain,thus providing a means of tuning the thermoresponsivity.Results of water permeability and rejection ratio versus temperature experiment suggesting that the pore sizes are controllable.The higher value of water flux recovery ratio?FRR?after flushing process at temperatures higher than the LCST demonstrate sustainable antifouling of blend membranes.The establishment of practicable strategy may be widely used in a system of water treatment and aimed to pave a new way to realize the large scale preparation of sustainable antifouling membranes.The blend membranes were prepared in a mixed coagulation bath and the effects of hydrophobic block copolymers on the surface morphology and properties of the membranes were investigated.Studies have demonstrated that the introduction of additives is conducive to the formation of micro-nanostructures on the surface of the blended membrane,reducing the surface free energy.The micro-nano rough structure is formed by the blend membrane can continuously separate and agglomerate the oil/water emulsion and finally achieve the effect of oil/water separation.In the separation of water-in-oil emulsion,the separation efficiency of the blend membranes for methylene chloride,toluene,and n-hexadecane is very high,and the purity of the filtrates is above 99%.Hydrophobic block copolymers increase the hydrophobic capacity of the blend membrane while also improving the corrosion resistance of PVDF.