Study On Synthesis And Properities Of Novel Aromatic Polyamides For Proton Exchange Membranes

As a core component of proton exchange membrane fuel cell (PEMFC), proton exchange membrane(PEM) influences the performance of the application and development of PEMFC. PEM acts as an electrolyte for transferring protons from the anode to the cathode as well as providing a barrier to electrons and gases cross leakage between the electrodes. Currently, perfluorinated proton-exchange membranes have been broadly used in PEMFC, such as Dupont Nafion, which exhibit relatively high proton conductivity when fully hydrated and display long term durability. But the high cost, high dependence on humidity and difficult to synthesis monomers limit their further use in PEMFC. Aromatic polymer such as poly(ether ether ketone), poly(arylene ether sulfone) and sulfonated polyimide, has excellent chemical stability, heat stability and aging properties, which can be used for proton exchange membranes as alternatives.In this dissertation, series of sulfonated aromatic polyamides were prepared by polycondensation of a CF3-containing diamine with various ratios of terephthalic acid and5-Sodiosulfoisophthalic acid. The resulting polyamides exhibited outstanding thermal stability. Membranes were prepared by solution casting, then characterized by determining ion-exchange capacity (IEC), water uptake, swelling ratio, proton conductivity and mechanical properties. With the gradual growth of sulfonic acid groups from70%to100%(molar ratio), IEC increased to1.0223meq/g, and proton conducticity reached up to3.82x10-2S/cm, while water uptake and swelling ratio remained in proper values.The tensile strength of SPAs membranes was beyond46.63MPa, but the elongation at break was in the range of2.81-11.89%, suggesting not enough tough of SPAs membranes used as PEM. Thus, in order to improve the mechanical properties of SPAs under fully hydrated condition, SPAs/POSS and SPAs/Boltorn H20blend membranes were prepared by adding POSS and hyperbranched polyester Boltorn H20to SPAs, respectively. It turned out that Boltorn H20contributed a lot to the mechanical performance of SPAs/Boltorn H20membranes. Both the tensile strength and the elongation at break of SPAs/Boltorn H20blend membranes increased, meanwhile, the water uptake increased and the swelling ratios decreased, which showed better dimensional stability than SPAs.The proton conductivity of SPAs/Boltorn H20membranes increased with the adding amount of Boltorn H20, and higher than that of SPAs membranes. From the field emission scanning electron microscopy (FE-SEM) spectra we can see that, hydrophobic Boltorn H20jointed the hydrophobic aromatic chains of SPAs through physical crosslinking and led to hydrophobic areas packing tightly, generating better microphase separation of hydrophilic domain and hydrophobic domain, which was conducive to the transmission of proton.