Polystyrenic 1H-tetrazole was previously investigated as an anhydrous proton conductor and found to have both promising conductivity and unique physical characteristics for an azole-containing homopolymer.  However, 1H-tetrazole retains bound water under operationally anhydrous conditions and exhibits a pKa similar to its biological congener, carboxylic acid.  Polystyrenic hexanoic acid has been synthesized and characterized to compare proton transport in 1H-tetrazole versus carboxylic acid-based ionic conductors.  Despite the abundance of biochemical comparisons of the two acids in the literature, physiochemical comparisons between these to moieties are rare, and comparisons as solid electrolytes are non-existant.Though 1H-tetrazoles and carboxylic acids have similar pKa, the properties of these two polymers are remarkably different.  Anhydrous conductivities are four orders of magnitude lower in the carboxylic acid-based polymer than in the 1H-tetrazole functionalized material.  When the materials are hydrated, this margin narrows only moderately.  Thermal analysis, solid state NMR, and analysis of conductivity, mobility, and charge carrier density come together to show that morphology, side chain and acid dynamics, and the mechanism of conductivity all differ markedly as a function of the tethered acid.  The combined amphotericity, propensity for hydrogen bonding, and polarity of 1H-tetrazole likely contribute to its large increase in conductivity compared to carboxylic acid-based proton conductors.

Weak acid congeners: Polymer bound 1<i>H</i>-tetrazole vs. carboxylic acid

247th National Meeting (2014)

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Weak acid congeners: Polymer bound 1H-tetrazole vs. carboxylic acid