The recent expansion in proton exchange membrane (PEM) research has been commensurate with the growth of PEM fuel cell research. Perfluorosulfonic acid (PFSA) ionomer materials remain the technological membrane of...
The
structure–property relationship of sulfonated phenylated
poly(phenylene)s possessing either angled or linear backbone moieties
was investigated. Polymers were synthesized using either bent (ortho or meta) or linear (para) biphenyl linkages and evaluated for differences in physical and
electrochemical properties. Model compounds, structurally analogous
to the polymers, were prepared and characterized using spectroscopic
and computational methods to elucidate structural differences and
potential impacts on the properties of the respective polymers. A
highly angled ortho biphenyl linkage resulted in
a sterically hindered, rotationally restricted molecule. When incorporated
into a polymer, the angled ortho biphenyl moiety
was found to prevent membrane formation. The angled meta biphenyl-containing polymer, while forming a membrane, exhibited
a 74% increase in volumetric expansion, 31% reduction in tensile strength,
and 72% reduction in elongation at break when compared to the linear para biphenyl-containing analogue. The differences observed
are attributed to a rotationally restricted backbone in the angled
biphenyl systems. Collectively, this study suggests that incorporating
angled biphenyl linkages into sulfonated phenylated poly(phenylene)s
leads to highly rigid, inflexible backbones that prevent chain entanglement
and the formation of free-standing membranes.
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