(30f) Star Poly(ionic liquid)s

Poly(ionic liquid)s (PILs) have been investigated as materials in electrochemical energy devices, such as batteries and fuel cells, due to their unique combination of properties (e.g., high ionic conductivity, wide electrochemical window, excellent chemical and thermal stability) and widely tunable polymer chemistry. However, to date, most investigations on PILs are exclusive to linear PILs. Star PILs may be of interest due to recently reported mechanical and electrochemical property enhancements in star polymer electrolytes compared to their analogous linear polymer electrolytes. However, there are only a few studies on ion-containing star polymers (i.e., ionic moiety covalently attached to polymer chain), where most previous studies on star polymer electrolytes are exclusive to neutral star polymers doped with ionic salt and/or ionic liquid. In this work, 3-, 4-, and 6-arm star-poly(vinylbenzyl chloride) homopolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The impact of radical initiator concentration and number of RAFT functional groups on the resulting polymer molecular weight and dispersity was investigated for targeted synthesis of uniform 3-, 4-, and 6-arm star homopolymers with similar length of polymer arms. Subsequently, novel star PILs with covalently attached imidazolium cations and mobile bis(trifluoromethane)sulfonimide counter anions were synthesized via quaternization and anion exchange of the precursor star homopolymers. The thermal, mechanical, and electrochemical properties of each star PIL were studied with respect to the number of polymer arms. Each of these properties were analyzed in comparison to its analogous linear PIL to investigate the impact of star architecture on the polymer performance. Additionally, the temperature-dependent ionic conductivities were analyzed with the Vogel-Fulcher-Tammann (VFT) and Williams-Landel-Ferry (WLF) equations to explore the conductivity-free volume relationships in star PILs compared to its linear analog.