We have identified the low solid-state conductivity of a series of synthesized poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA) homopolymers, 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. Electrically, we find that PTMA is highly insulating – conductivity in the range 10 <sup>-11</sup> S/cm – regardless of the synthetic method of preparation. We have compared these results with variable range hopping theory and find that very few radical sites are electrically active, though the stable radical sites are closely packed.<br/>For charge storage applications that take advantage of the redox-active nature of stable radical polymers, enhanced conductivity would improve performance. The replacement of an insulating backbone of PTMA with a conducting polymer backbone can be a strategy to improve the poor electron transport in a solid PTMA film. To address this issue, we prepared and studied soluble polythiophene with high regioregularity and varied the concentration of pendent radical groups to systematically examine the variation of conductivity with radical incorporation. Using EPR and electrical conductivity measurements, we showed that there is an exponential decrease of conductivity as we increased the percentage of pendent groups attached to repeating units, which changes the conductivity by 6 orders of magnitude between the non-radical control polythiophene material and the material with the highest radical content (~80%). The conductivity of the solid films can be further improved by doping with oxidizers. These findings serve as an important guide for the future design of radical polymers on conjugated backbones with the goal of increasing conductivity for redox-active energy storage applications.

Synthesis and charge transport study of polymers with stable radical substituents

256th National Meeting (2018)

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