Synthesis of A Novel Spirobisnitroxide Polymer and its Evaluation in an Organic Radical Battery

Abstract

A straightforward synthesis of a novel spirobisnitroxide <strong>6</strong> has been developed. Cyclovoltammetry of <strong>6</strong> revealed two distinct reversible oxidation/reduction steps separated by ca. 740 mV indicating the formation of the corresponding oxoammonium cations. Rhodium-catalyzed polymerization of <strong>6</strong> afforded the polyacetylene polymer <strong>7</strong> bearing the pending spirobisnitroxide groups. Additionally, cross-linked <strong>7</strong> was prepared in the presence of 3 mol % of <em>N</em>,<em>N</em>′-diprop-2-ynyl-oxalamide. If oxidation of both nitroxide groups is considered, <strong>7</strong> possesses an unprecedented high theoretical charge capacity of 174 mA h g⁻¹. Evaluation of the cross-linked polymer <strong>7</strong> as a cathode material for an organic radical battery showed very good cycling stability when the potential was kept below the oxidation potential of the five-membered nitroxide subunit of <strong>6</strong>. A presumable irreversible degradation of the polymeric backbone of <strong>7</strong> occurred at higher potentials, limiting the experimentally obtained charge capacity to 73 mA h g⁻¹.