Redox-Active Verdazyl Radical Polymers via Postpolymerization Modification of Active Ester Polymers

Organic radical polymers (ORPs) are constructed with 1,5-dimethyl-6-oxoverdazyl radicals for assessment as redox-active materials. The ORPs were synthesized through the postpolymerization modification (PPM) of poly(pentafluorophenyl methacrylate) (P1) and poly(pentafluorophenyl acrylate) (P2) with either 1,5-dimethyl-3-(p-aniline)-6-oxoverdazyl (1), 1,5-dimethyl-3-(4-methylamine-(1,1'-biphenyl))-6-oxoverdazyl (2) or 1,5-dimethyl-3-(4-methylamine-(1,1'-biphenyl))-6-oxoverdazyl (3). To overcome the limited stability of 1, radicals containing bulky C₃ substituents and alkyl spacers to the heteroatom of the 4-methylamine or 4-hydroxymethyl moiety were synthesized from high yielding (78%-98%) Suzuki-Miyaura cross-couplings. The large cell potential (E°_cell(3) = 1.67 V) and radical stability ensure these are well suited to fundamental electrochemical proof of concept studies when incorporated into a polymer. Variable radical attachment (0%-75%) was observed in PPM reactions. The ester aminolysis of P2 yielded the highest radical containing polymer (P2-2; 75%). As a proof-of-concept electrochemical demonstration, P2-2 and P2-3 exhibited a reversible redox couple at 3.43 V (vs. Li/Li⁺), successfully validating the redox activity of the verdazyl-functionalized polymers in a coin cell.