Synthesis And Characterization Of Sulfonated Aromatic Copolymers With Phosphine Oxides For Proton Exchange Membranes

Proton exchange membranes（PEMs）are one of the indispensable components for proton exchange membrane fuel cells.Currently,Nafion membrane is the most widely used one for proton exchange membrane fuel cell because of its excellent comprehensive performance.However,Nafion membrane also has some shortcomings,which can inhibited its industrial application in proton exchange membranes.Therefore,looking for alternative membranes has become a hot spot in current research.Sulfonated aromatic polymers,such as poly（arylene ether phosphine oxide）s,have attracted attentions because of their excellent comprehensive properties and the potential values of becoming matrix materials for PEM.In chapter 2,from the view of the polymer structure design,a series of sulfonated aromatic copolymers containing phosphine oxide and bisphenol（sPOPH-x）with different sulfonation degrees were synthesized via direct polycondensation of hydroquinone with bis（4-fluorophenyl）phenyl phosphine oxide and potassium2,5-dihydroxybenzene sulfonate monomers.These polymers could be cast into the uniform and tough membranes.And the characterizations of the obtained membranes were invested detailed.The resulting membranes showed excellent properties.For example,sPOPH-55 displayed a conductivity of 0.086 S cm^-1at 80℃,which is comparable to that(0.089 S cm^-1)of Nafion 117.In addition,it began to dissolve after65 hours in Fenton’s reagent（30℃,30%H₂O₂containing 30 ppm Fe SO₄）,indicating good oxidation resistance.However,as the degree of sulfonation increases,the swelling ratio of the film at higher temperatures is not ideal.In chapter 3,a series of sulfonated poly（arylene ether phosphine oxide）with different sulfonation degrees were synthesized by direct polycondensation of9,9-bis（4-hydroxyphenyl）fluorine and bis（4-fluorophenyl）phenyl phosphine oxide with potassium 2,5-dihydroxybenzenesulfonate monomers（sPOPF-x）.The proton exchange membranes were prepared by solution casting method.On the basis of the research in chapter 2,the bisphenol monomer was replaced by the large hydrophobic group of diphenylfluorenyl in order to further improve the overall performance of the membrane.The overall properties of the resulting membranes were investigated.For example,sPOPF-x has excellent oxidation stability.The membrane was soaked in Fenton’s reagent（30%H₂O₂,30 ppm Fe SO₄）at 30℃ for 72 hours.It remained intact and there was no significant change in appearance.At 80℃,the water absorption rate of sPOPF-65 is 36.3%,slightly higher than Nafion117（30%）at the same temperature,but its swelling rate is 16.4%,which is much lower than Nafion117（20%）.Moreover,its proton conductivity rate is 0.085 S cm^-1,which is equivalent to Nafion117.