Design And Structure-Property Relationship Studies Of Novel Poly (Arylene Ether) As Proton Exchange Membranes

Title: Design and structure - property relationship studies of novel poly(arylene ether) as proton exchange membranesMajor: Polymer Chemistry and PhysicsAdviser: Pro. Jiang ZhenhuaHydrocarbon sulfonated aromatic membranes, particularly sulfonated poly(aryl ether)s, have attracted attention as potential candidates as membrane applied to the production of energy and of clean water. They represent an attractive alternative to perfluorinated sulfonic acid membranes for high temperature proton-exchange membrane fuel cells because of their excellent stability and high glass transition. An increase of the operating temperature to above 100oC promises crucial benefits conceming the complexity, cost and performance of automotive PEMFC systems. Water managenment would be reduced. The properties and durability of fuel cell core components must be further improved to meet market expectations.Early examples of sulfonated poly(aryl ether)s, sulfonic acid were obtained by post-polymerization sulfonation. For high acid content the excessive water swelling and even water solubility of these ionomers limit their applicability. Partial sulfonation results in acid groups that are distributed statistically along the polymer backbone. Unlike perfluorosulfonic acid these hydrocarbon membranes do not usually exhibit the formation of connected water-filled channels that promotes efficient transport of proton across the membrane. A similar issue arose in the case of sulfonated poly(aryl ether)s prepared by polymerization of pre-sulfonated monomers. In this case, high water swelling is avoided by the use of non-sulfonated co-monomers. Therefore, the resulting polymers also had an irregular distribution of sulfonic acid along the polymer backbone. It has been demonstrated that controlling the distribution and location of sulfonic acid can result in well-defined hydrocarbon membrane morphology. As a result of the formation of connected water-filled channels, such membranes have superior proton-conducting properties than statistically sulfonated membranes, particularly at low relative humidity.There are three parts of our research work. First one , Brominated poly(ether sulfones) were prepared and investigated for use as proton-conducting fuel-cell membranes. In the first step, 4-bromophenylquin -one (Br-PQ) and 4-bromophenylhydroquinone(Br-PH) were synthesized according to a previously reported synthetic procedure. Next, poly (ether sulfones) with a 4-bromophenyl pendant group was synthesized based on a bromo-bisphenol. Finally, Brominated poly(ether sulfones) was coupled by dehalogenation with potassium 1,1,2,2-tetrafluoro-2- (1,1,2,2-tetrafluoro-2- iodoethoxy)ethanesulfonate (PSA-K) using copper metal, followed by treatment with aqueous HCl.Second, A series of six sulfonated poly(aryl ether sulfone)s with a strictly alternating repeat unit have been prepared and evaluated as proton conducting membranes. Two efficient and simple synthetic strategies are described to obtain bisphenol monomers composed of four or six phenylene units linked by ether bridges that cannot be subjected to transetherification. Polycondensation of these bisphenol monomers with sulfonated dihalide monomers gave high molecular weight homopolymers. The sulfonated moieties of these homopolymers are separated by monodisperse non-sulfonated spacers corresponding to the bisphenol oligo(ether) monomers. Membranes was obtained by solvent casting method and were characterized by titration, impedance spectroscopy, DSC and TGA. The properties of the membranes were closely related to the connectivity of the non-sulfonated spacers. At identical acid content, the membranes containing meta ether linkages had a lower glass transition than all-para materials. Greater chain mobility resulted in superior proton conductivity. Under 100% relative humidity at 80°C, these materials had proton conductivity up to 216 mS/cm-1. The membrane with an acid content of 2.05 meq g-1 containing exclusively Para linkages had a proton conductivity similar to Nafion together with an excellent stability in boiling water.Finally, cyanide and sulfone groups were introduced in the polymer main chain, and obtained micro block copolymers with the two functional groups were investigated in detailly. The Excellent thermal stability was observed by DSC and TGA. Swelling test results showed that the copolymers have good dimensional stability in specific humidity, specific temperature. The obtained bifunction polymer film exhibited high proton conductivity means our new materials have wide range of applications.