There are conflicting reports in the literature about the presence of room temperature conductivity in poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA), a redox active polymer with radical groups pendent to an insulating backbone. To understand the variability in the findings across the literature and synthetic methods, we prepared PTMA using three living methods - anionic, ATRP and RAFT polymerization. We find that all three synthetic methods produce PTMA with radical yields of 70 - 80%, controlled molecular weight, and low dispersity. Additionally, we used on-chip EPR to probe the robustness of radical content in solid films under ambient air and light, and found negligible change in the radical content over time. Electrically, we found that PTMA is highly insulating - conductivity in the range 10- S/cm - regardless of the synthetic method of preparation. These findings provide greater clarity for potential applications of PTMA in energy storage.

Synthesizing a stable radical polymer with a conjugated backbone seems like a natural way to introduce conductivity to radical polymers, which are traditionally synthesized with insulating, nonconjugated backbones. For charge storage applications that take advantage of the redox-active nature of stable radical polymers, enhanced conductivity would improve performance. To explore the interplay between stable radicals and a conjugated backbone, we prepared and studied soluble polythiophene with high regioregularity and various concentrations of pendent radical groups to systematically examine any change in conductivity with radical incorporation. Using electron paramagnetic resonance and electrical conductivity measurements, we show that there is an exponential decrease in conductivity as we increase the percentage of pendent groups attached to repeating units, which changes the conductivity by 6 orders of magnitude between the nonradical control polythiophene material and the material with the highest radical content (∼80%). These findings serve as an important guide to the future design of radical polymers on conjugated backbones with the goal of tuning conductivity as a function of stable radical content in redox-active energy storage applications.

We investigate the thermoelectric properties of a T-shaped double quantum dot system described by a generalized Anderson Hamiltonian. The system's electrical conduction (G) and the fundamental thermoelectric parameters such as the Seebeck coefficient (S) and the thermal conductivity (κ), along with the system's thermoelectric figure of merit (ZT) are numerically estimated based on a Green's function formalism that includes contributions up to the Hartree-Fock level. Our results account for finite onsite Coulomb interaction terms in both component quantum dots and discuss various ways leading to an enhanced thermoelectric figure of merit for the system. We demonstrate that the presence of Fano resonances in the Coulomb blockade regime is responsible for a strong violation of the Wiedemann-Franz law and a considerable enhancement of the system's figure of merit (ZT ).