Poly(Ionic Liquid) ABC Triblock Terpolymers: Targeted Synthesis and 3D Network Morphologies

Abstract

Solid-state polymer electrolytes (SPEs) that are highly conductive, strong, and electrochemically stable are required to enable safe, long-lasting lithium-ion batteries. Poly(ionic liquid) (PIL) block copolymers are excellent SPE candidates because they combine the unique physiochemical properties of ionic liquids (e.g., electrochemical stability) and the nanostructure (i.e., morphology) of block copolymers. Previously, PIL AB diblock copolymers revealed that morphology type influences the ionic conductivity (a property related to battery capacity), where the 3D network (continuous) morphology yielded the highest ionic conductivity. However, the 3D network morphology occurs over a narrow composition range in PIL AB diblock copolymers. PIL ABC triblock terpolymers have yet to be explored and potentially yield multiple unique 3D network morphologies over a much broader compositional range. In this work, a mathematical model of reversible addition-fragmentation chain-transfer (RAFT) polymerization was developed, which predicts the synthesis of PIL ABC triblock terpolymers. Leveraging the model results, 17 compositions of the PIL ABC triblock terpolymer, poly(S-b-VBMIm-TFSI-b-HA) (S = styrene, VBMIm-TFSI = vinylbenzyl methylimidazolium bis(trifluoromethylsulfonyl)imide, HA = hexyl acrylate), were synthesized and characterized for their morphologies, revealing a broad 3D morphology compositional window at 0.5 < fVBMIm-TFSI < 0.6, 0.05 < fHA < 0.1, and 0.35 < fS<0.4. Overall, this work demonstrates the first ion conducting triply periodic structures in polymers and a larger compositional window for 3D continuous morphologies in PIL ABC triblock terpolymers.