Charge and mass transfer are key functionalities of redox-active polymers, impacting applications in energy storage. Tacticity affects polymer chain conformation and mobility, free volume, and redox unit spacing, but the consequences on their ability to store charge remain unclear. Here, we control tacticity in poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA) and demonstrate its decisive influence on electrochemical properties. Isotactic, atactic, and syndiotactic PTMA with mm ∼80%, mr or rm ∼44%, and rr ∼77% configurations, respectively, are synthesized by anionic polymerization. Overall, isotactic PTMA possessed the highest specific capacity and energy -37% higher than syndiotactic PTMA at 5C. Electrochemical analysis of the reaction diffusion and kinetics, as well as electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) analysis of the mass transfer process, reveal that specific capacity and energy are influenced by both processes. Of the three polymers studied, isotactic PTMA exhibited moderate charge transfer kinetics but the least mass transferred in the redox reaction. Meanwhile, atactic PTMA exhibited the fastest kinetics but the most mass transferred. All-atom molecular dynamics (MD) simulations explain this effect, showing that atactic PTMA bears the lowest density and the greatest conformational heterogeneity, leaving greater free volume for solvated ion (de)insertion. This work highlights that tacticity is an important consideration in developing next-generation nonconjugated redox-active polymers for electrochemical energy storage.
Avais et al. (Mon,) studied this question.