Siddhartha Akkiraju obtained his B.S. in chemical engineering in 2017 from the University of California, San Diego. While in undergrad
he worked in Professor Ratnesh Lal’s group on the synthesis and functionalization of Janus nanoparticles. After arriving at Purdue, he joined Professor Bryan Boudouris’ group. At Purdue he studies the structure-property relationships of radical polymers
to design and develop the next generation of macromolecules for organic electronic devices.
Recently, there has been significant increase in research and development in the field of organic electronics. This is mainly because organic electronic devices can
be flexible, lightweight, and processed from solution using low-cost manufacturing techniques. Typically, these devices have utilized conjugated polymers as their active layer components. This approach has been successful, but the use of conjugated polymers
comes with limitations. To address these limitations and expand the field of organic electronics, this work studies a novel class of macromolecules, radical polymers. Unlike their conjugated polymer counterparts, radical polymers are comprised of a non-conjugated
backbone with stable open-shell groups at their pendant sites.
This work quantifies the electron exchange behavior of poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO). Due to the high number of pendant open-shell
sites, PTEO displays strong paramagnetic behavior. Electron paramagnetic resonance spectroscopy revealed that 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxy (TEMPO-OH), 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEO), and PTEO showed rapid electron
exchange between the pendant radical groups. When compared to TEMPO-OH and TEO, there was more interaction between the unpaired electrons in PTEO due to their proximity along the polymer chain. This phenomenon was confirmed through magnetic susceptibility,
Xm, measurements between 2 K and 300 K. At 2 K, TEMPO-OH and TEO had a Xm of 1.8×10-2 emu mol-1 and 4.6×10-2 emu mol-1. PTEO on the other hand, had a Xm of 1.3×10-1 emu mol-1. Due to its amorphous nature, PTEO had weak antiferromagnetic interactions. However,
thin films of PTEO with TEMPO-OH additives showed increased antiferromagnetic interactions between the open-shell sites as well as stronger magnetoresistance effects.
In conclusion, radical polymers offer researchers an opportunity to explore an underutilized class of macromolecules. By studying the
structure-property relationships, we can gain better insight into radical polymers and develop novel materials for the next generation of organic electronics.
