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The Influence of Aromatic Disulfonated Random and Block Copolymers' Molecular Weight, Composition,and Microstructure on the Properties of Proton Exchange Membranes for Fuel Cells

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dc.contributor.authorLi, Yanxiangen
dc.contributor.committeechairMcGrath, James E.en
dc.contributor.committeememberRiffle, Judy S.en
dc.contributor.committeememberTaylor, Larry T.en
dc.contributor.committeememberDillard, John G.en
dc.contributor.committeememberDavis, Richey M.en
dc.contributor.departmentMacromolecular Science and Engineeringen
dc.date.accessioned2014-03-14T20:16:20Zen
dc.date.adate2007-09-27en
dc.date.available2014-03-14T20:16:20Zen
dc.date.issued2007-08-31en
dc.date.rdate2010-10-08en
dc.date.sdate2007-09-16en
dc.description.abstractThe purity of the disulfonated monomer, such as 3,3"-disulfonated-4,4"-dichlorodiphenyl sulfone (SDCDPS), was very important for obtaining high molecular weight copolymers and accurate control of the oligomer's molecular weight. A novel method to characterize the purity of disulfonated monomer, SDCDPS, was developed by using UV-visible spectroscopy. This allowed for utiliziation of the crude SDCDPS directly in the copolymerization to save money, energy, and time. Three series of tert-butylphenyl terminated disulfonated poly(arylene ether sulfone) copolymers (BPSH35, 6FSH35, and 6FSH48) with controlled molecular weightsï¼ Mnï¼ , 20 to 50 kg·mol-1, were successfully prepared by the direct copolymerization method. The molecular weight of the copolymer was controlled by a monofunctional monomer tert-butylphenyl, and characterized by the combination of 1H NMR spectra and modified intrinsic viscosity measurements in NMP with 0.05 M LiBr, which was added to suppress the polyelectrolyte effect. The mechanical properties of the membranes, such as the modulus, strength and elongation at break, were improved by increasing the molecular weights, but water uptake and proton conductivities found insensitive to copolymers" molecular weights. Three series of disulfonated poly(arylene ether ketone) random copolymers have been synthesized and comparatively studied, according to their different chemical structures, for use as proton exchange membranes. The copolymers containing more flexible molecular structures had higher water uptake and proton conductivity than the rigid structures at the same ion exchange capacity. This may be due to the more flexible chemical structures being able to form better phase separated morphology and higher hydration levels. A new hydrophobic-hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. AFM images and the water diffusion coefficient results confirmed that the multiblock copolymer formed better proton transport channels. This multiblock copolymer showed comparable proton conductivity and fuel cell performance to the Nafion® control and had much better proton transport properties than random ketone copolymers under partially hydrated conditions. This suggested that the multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity.en
dc.description.degreePh. D.en
dc.identifier.otheretd-09162007-203027en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-09162007-203027/en
dc.identifier.urihttp://hdl.handle.net/10919/28995en
dc.publisherVirginia Techen
dc.relation.haspartYanxiangLiDissertation.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectmolecular weighten
dc.subjectpoly(arylene ether sulfone)en
dc.subjectmorphologyen
dc.subjectmultiblocken
dc.subjectrandomen
dc.subjectpoly(arylene ether ketone)en
dc.subjectdisulfonated copolymersen
dc.subjectproton exchange membraneen
dc.subjectfuel cellen
dc.titleThe Influence of Aromatic Disulfonated Random and Block Copolymers' Molecular Weight, Composition,and Microstructure on the Properties of Proton Exchange Membranes for Fuel Cellsen
dc.typeDissertationen
thesis.degree.disciplineMacromolecular Science and Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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