Abstract: Designer macromolecules provide a platform by which to generate structured, multifunctional materials with tailored biochemical, redox, electrochemical, and optoelectronic properties. As such, they offer the promise of providing made-to-order, low-cost materials solutions to some of the most pressing polymer and soft materials challenges facing the world today. Here, we focus on the computational design, synthesis, molecular characterization, and the electronic, electrochemical, and spin device application of an emerging class of macromolecules, radical polymers. These open-shell macromolecules are of two types. The first of these are nonconjugated radical polymers (i.e., macromolecules lacking conjugation along their backbones and with stable open-shell sites present at their pendant groups). In these systems, we first highlight how the charge transport mechanism is distinctly different in radical polymers relative to classic conjugated polymers. Importantly, the charge carriers in radical polymers are singlet cations, and the presence of anomalous magnetoresistance in these materials highlights the potential upside of these advanced polymers in next-generation device applications. That is, we demonstrated that the solid-state electrical conductivity of a designer radical polymer, poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) PTEO, exceeds 20 S m-1, and this places this nonconjugated polymer conductor in the same regime as many grades of common commercially available, chemically doped conjugated conducting polymers. In addition, we employed ferromagnetic resonance spin pumping in a ferromagnet/ PTEO/ non-magnetic spin-sink trilayer device to demonstrate the importance of PTEO in carrying pure spin-current that results in large (i.e., some of the highest reported) inverse spin Hall effect (ISHE) voltages that are difficult to achieve with organic systems. Finally, we demonstrate that radical polymers transport pure spin currents, and that the nature of these materials yields systems with spin diffusion lengths on the order of 100 nm. In a second class of open-shell macromolecules, an electron donor-acceptor repeat unit motif is employed to create conjugated polymers with low bandgap energies. These narrow bandgap energy values impart an open-shell quality to the conjugated radical polymers at room temperature. These intrinsic conductors have relatively high electrical conductivities and display spin diffusion lengths > 1 µm. These key initial demonstrations highlight the potential for open-shell polymers as solid-state charge conductors and in next-generation quantum information systems.

Bio: Bryan W. Boudouris is the Vice President for Research & Economic Development and a professor in the Department of Chemical & Biological Engineering at The University of Alabama, roles he has held since April 2024. Prior to Alabama, he was the R. Norris and Eleanor Shreve Professor of Chemical Engineering in the Charles D. Davidson School of Chemical Engineering and a professor (by courtesy) in the Department of Chemistry at Purdue University where he also served as the Associate Vice President for Strategic Interdisciplinary Research. From 2020-2022, he served on an Intergovernmental Personnel Act (IPA) assignment as a Program Director in the Division of Materials Research at the National Science Foundation. He received his B.S. in Chemical Engineering from the University of Illinois at Urbana-Champaign in 2004. After receiving his Ph.D. in Chemical Engineering from the University of Minnesota in 2009, he conducted postdoctoral research from 2009 to 2011 at the University of California, Berkeley and Lawrence Berkeley National Laboratory. Since starting his independent career at Purdue University in 2011, he has been the recipient of many awards including the AFOSR YIP award, the DARPA YFA, the NSF CAREER Award, the AIChE Owens Corning Early Career Award, the Saville Lectureship at Princeton University, and the John H. Dillon Medal from the APS.