(486c) Increased Hydrophobic Content Multiblock Copolymers for Use As Proton Exchange Membranes in Direct Methanol Fuel Cells (DMFC)s

Two series of increasing hydrophobic poly(arylene ether nitrile) and poly(arylene ether ketone) oligomers were successfully synthesized. These poly(arylene ether) hydrophobic oligomers consistent of different amounts of methyl groups on the bisphenol A co-monomer (bisphenol A, dimethyl bisphenol A, and tetramethyl bisphenol A), and were combined with either difluorobenzonitrile or difluorobenzophenone to from the hydrophobic segments. In addition to further increase the hydrophobicity of the moieties, small mole percent’s of the bisphenol A monomer series (0-25%) were replaced by the fluorinated bisphenol A analog 4,4’-hexafluoroisopropylidenediphenol. Only up to twenty-five percent of the fluorinated monomer was used in the hydrophobic copolymers due to the concern over methanol cross-over, which has been shown to greatly increase with higher fluorine content.

  Both series of hydrophobic oligomers were then reacted with a poly(arylene ether sulfone) hydrophilic oligomer (BPS100) via a low temperature coupling reaction to produce the hydrophilic-hydrophobic alternating multiblock copolymers. The resultant block copolymers formed a tough, durable, and transparent membrane when cast from solution, with structure confirmation and composition done using ¹H and ¹³C NMR spectroscopy. Mechanical properties were examined using tensile testing, and used in combination with size exclusion chromatography (SEC) to confirm high molecular weight was achieved.  In addition the conductivity, swelling ratio, and fuel cell performance was measured and compared against that of the nafion membrane. Membrane electrode assembly (MEA) and fuel cell performance was carried out by Los Almas National Laboratory (LANL) in collaboration with this work. The synthesis and characterization of these multiblock copolymer membranes will be discussed.