Preparation And Properties Of Sulfonated Poly (Fluorene Ether Nitrile Sulfone)s With Pendant Amion Groups And Its Composite Membranes

Proton exchange membrane fuel cells?PEMFCs?have potential to become new type of electrochemical devices by virtue of high energy conversion efficiency and low greenhouse gas emissions.As one of the vital component of polymer electrolyte membrane fuel cell,proton exchange membrane?PEM?acted as a proton conductor as well as a separator between the anode and cathode chambers in fuel cells.The properties of proton exchange membranes have direct impact on the qualities of fuel cells.Novel membrane materials with improved performance have expected to surmount the barriers of commercial Nafion.Sulfonated aromatic polymers have attracted wide concern due to their outstanding thermal stability and chemical stability.In order to solve the problem of poor dimensional stability and severe methanol permeability in water environment caused by excessive swelling under high sulfonation degrees of sulfonated aromatic polymers,crosslinking is an effective way to enhance the interaction of polymer chains to form a compact membrane structure and maintain dimensional stability.Meanwhile,the introduction of rigid hydrophobic groups can also relieve excessive swelling.In chapter three,4-aminophenyl hydroquinone was firstly synthesized by diazo reaction.Then sulfonated poly?fluorene ether nitrile sulfone?s containing pendant amino groups?Am-SPFENS?were prepared by polycondensation reaction.Amino groups,sulfonate groups,nitrile groups and fluorene groups were introduced into the same polymer chains.The performance of the membrane can be reinforced by adjusting the strutrue of the polymer.The direct condensation method can precisely control the sulfonation degree of the copolymers by immobilizing the feeding ratio between sulfonated monomers and nonsulfonated monomers,and also avoid the side reactions such as crosslinking and degradation of the main chains compared with the post-sulfonation method.The presence of ponderous fluorenyl groups in the main chain have been constructed the hydrophobic polymer framework to limit the excessive swelling of the membrane and elevated the oxidation stability of membranes by resisting the attack from oxidants through steric effect.Nitrile groups have contributed to strong nitrile dipole interchain interactions and a self-crosslinked structure for copolymers on account of high dipole moments.The involvement of nitrile groups could enhance the intra/intermolecular interaction and increase the aggregation of the functional groups.Thereby,intergrating nitrile groups to polymers could depress the excessive swelling and maintain dimensional stability.The existence of acid-base interaction between pendant amino groups and sulfonate groups in the copolymer is beneficial for the formation of compact membranes structrue,which restrains methanol permeability and controls the methanol permeation coefficient of the membrane within the range of 8.05¹6.06×10^-7 cm² s^–1.The proton conductivity of Am-SPFENS reached to 0.081 S cm^-1 at 80?,which is higher than that of Am-SPAEKS at the same condition(0.071 S cm^-1).To further improve proton conductivity,a series of sulfonated poly?fluorene ether nitrile sulfone?containing pendant amino groups?Am-SPFENS?/phosphotungstic acid?HPW?composite membranes with different HPW content were prepared by the solution blend method.HPW is well known as a proton conductor and can be easily removed in water because of its high water solubility.The existence of acid-base interactions between amino groups and HPW particles,adsorption effects of nitrile groups to HPW particles,hydrogen-bond interactions between HPW particles and sulfonic groups,as well as a self-crosslinked structure for copolymers stabilized HPW in composite membranes.The interaction and crosslinking network in the polymer chain not only improved the proton conductivity,but also maintained the oxidation stability of composite membranes.The proton conductivity of Am-SPFENS/HPW30%composite membranes reached to 0.098 S cm^-1 at 100?.The results suggest that these composite membranes have potential as proton exchange membranes for applications in medium-high-temperature fuel cells.