TEMPO-based organic radical polymers such as poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) are important polymers in organic radical batteries owing to their ease of synthesis and fast transport properties. In particular, electrodes comprised of polymers containing stable radicals have become attractive for organic radical batteries. These constructs are fabricated from a solution, and thus elucidating the conformation of PTMA in solvents that are relevant to their use in batteries is needed. Consequently, we used small-angle neutron scattering to determine the conformation and thermodynamic interactions of PTMA in two solvents, deuterated N-methyl-2-pyrrolidone (d-NMP) and a 50/50 (wt.%) mixture of deuterated ethylene carbonate/deuterated dimethyl carbonate (d-EC/d-DMC). The impact of temperature and radical loading on the polymer solvent interactions and PTMA conformation in each solvent were also studied. Zimm analysis shows that d-NMP is a better solvent for PTMA than the carbonate mixture. This analysis also shows that increasing the radical loading in the PTMA decreases the quality of the solvent, as evidenced by a decrease in the second Virial coefficient. Kratky plot analysis revealed that PTMA with 68% radical loading is partially collapsed in d-NMP at room temperature, but expands and acts as a semi-flexible polymer at 60°C. On the other hand, this polymer behaves like a semi-flexible polymer in d-EC/d-DMC at both 25°C and 60°C. Similar Kratky plot analyses of PTMA with 98% radical loading shows that this polymer attains a semi-flexible polymer chain conformation in NMP. At the same time, the dependence of radius of gyration on molecular weight analysis indicates that the PTMA with 98% radical loading is quite rigid in NMP. Correlation of these structural and thermodynamic observations to the performance of the PTMA in electrochemical applications is also underway.

Effect of radical content on the conformation of TEMPO-based organic radical polymers in application-relevant solvents

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.