Design of n-type Radical Polymers and Their Utilization as Solid-State Conductors

Radical polymers are receiving increasing attention due to their ability to transport charge in solid state. However, the radical polymer conductors evaluated to date have been almost exclusively based on (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO); thus, macromolecules bearing preferentially-reduced (i.e., n-type) radicals have received little attention. Herein, phenoxy-based, n-type radical polymers featuring ethylene oxide-based and siloxane-based backbones are developed. Their singly occupied molecular orbital energy level is around 4.7 eV removed from vacuum. Moreover, the spin-spin interaction among the intra-chain radical groups was quantified using electron paramagnetic resonance (EPR) spectroscopy. In addition, the glass transition temperatures for these polymers are below room temperature due to their flexible macromolecular backbones. Furthermore, the solid-state conductivity values of thin films of these radical polymers reach values up to 0.01 S m^-1, demonstrating the potential of these materials as future solid-state conductors. In this way, we have determined the fundamental physics that dictates transport in nonconjugated, n-type radical polymers and help to establish the solid-state conducting performance for an emerging class of n-type radical polymers.