Polyethylene structures containing precisely placed phosphonic acids were synthesized varying both the frequency of acid appearance along the backbone and the architecture associated with each position. Single, geminal, and benzyl attachment schemes are described with symmetry of placement being an important feature. Altering these precision primary structures has a direct effect on secondary structure where changes in thermal behavior become obvious, particularly in terms of crystallization behavior. It is evident that strong interactions between polymer chains exist, effecting polymer crystallization and solubility depending upon both the length of methylene run-lengths between symmetrically placed acids and whether or not the acid group is protected as the ester or free to participate in hydrogen bonding, which directly influences interchain interaction.
Two novel phosphonic acid-based "dry" proton exchange membrane materials that may allow for fuel cell operation above 100 degrees C have been prepared and characterized via solid-state 1H and 2H MAS NMR spectroscopy. We obtained information on both the nature of hydrogen bonding and local proton mobilities among phosphonic acid moieties. In particular, 2H MAS NMR line shape analysis yielded apparent activation energies of the underlying motional processes. Using this approach, we have investigated both a model compound and a novel PEM system. It was found that the relation of estimated hydrogen-bond strength and local proton mobility accessible by solid-state NMR and bulk proton conductivity is complex. Improvements through admixture of a second component with protogenic groups are suggested.
New polymer electrolyte membranes for fuel cell applications were synthesized via covalent bonding of phosphonic acid (PA) onto poly(benzimidazole) (PBI). PBI was functionalized via N‐alkylation with an appropriate phosphonate, followed by hydrolysis of the grafted groups to the desired PA functions. Alternatively, polymer networks based on PBI and vinyl phosphonic acid (VPA) were successfully synthesized. In this second approach, PBI was first functionalized in a polymer analogous modification with polymerizable or radical‐forming groups. Thermally induced ‘grafting‐through’ or ‘grafting‐from’ polymerization of VPA led to the corresponding PBI/PVPA networks. The structure‐property relationships with respect to proton conducting properties of the membrane materials are discussed.magnified image
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.