Title page for ETD etd-04032008-043523

Type of Document Dissertation
Author Yu, Xiang
Author's Email Address xiangyu@vt.edu
URN etd-04032008-043523
Title Synthesis and Characterization of Hydrophilic-Hydrophobic Disulfonated Poly(Arylene Ether Sulfone)-Decafluoro Biphenyl Based Poly(Arylene Ether) Multiblock Copolymers for Proton Exchange Membranes (PEMs)
Degree PhD
Department Macromolecular Science and Engineering
Advisory Committee
Advisor Name Title
McGrath, James E. Committee Chair
Case, Scott W. Committee Member
Davis, Richey M. Committee Member
Dillard, John G. Committee Member
Riffle, Judy S. Committee Member
  • Nanophase separation
  • Morphology
  • Poly(arylene ether sulfone)s
  • Fuel cells
  • Proton exchange membranes
  • Multiblock copolymers
  • Fluorinated copolymers
Date of Defense 2008-01-21
Availability unrestricted
Hydrophilic/hydrophobic block copolymers as proton exchange membranes (PEMs) has become an emerging area of research in recent years. Three series of hydrophilic/hydrophobic, fluorinated/sulfonated multiblock copolymers were synthesized and characterized in this thesis. These copolymers were obtained through moderate temperature (~100°C) coupling reactions, which minimize the ether-ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The hydrophilic blocks were based on the nucleophilic step polymerization of 3,3’-disulfonated, 4,4’-dichlorodiphenyl sulfone with an excess 4,4’-biphenol to afford phenoxide endgroups. The hydrophobic (fluorinated) blocks were largely based on decafluoro biphenyl (excess) and various bisphenols. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure-property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to the ionic proton conducting channels formed through the self-assembly of the sulfonated blocks. The nano-phase separated morphologies of the copolymer membranes were studied and confirmed by atomic force microscopy. Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state-of-the-art PEM, Nafion, were achieved.
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