Radical Polyesters: Connecting Spacer Structure to Bulk Electrical Conductivity

Electron exchange communication between nitroxide radical sites localized along polymer backbones creates a compelling platform for spin electronics, resistive memory, and optoelectronics. While radical site proximity, chain flexibility, and local ordering form the basis for this communication, how site-to-site spacer structure governs bulk redox charge transfer remains an open question. Herein, epoxide-cyclic anhydride ring-opening copolymerization produces TEMPO-functional radical polyesters, where strictly alternating enchainment installs a radical at every repeat unit while anhydride comonomer varies spacer structure from flexible aliphatic through alicyclic, bicyclic, and semiaromatic. SQUID magnetometry and EPR spectroscopy confirm radical contents of 86-98%; except for the thioether-containing polyester, where sulfur-specific quenching occurs. Density functional theory calculations reveal that rigid aromatic spacers position radical sites closer than flexible aliphatic ones of comparable through-bond atom counts. However, solid-state electrical conductivity measurements demonstrate that glass transition is the primary determinant of bulk charge transport, regardless of whether it is set through spacer flexibility, blending, or block copolymerization.