(542g) Poly(ionic liquid) ABC Triblock Terpolymers

Poly(ionic liquid) (PIL) block copolymers synergistically combine the unique physiochemical properties of ionic liquids (e.g., high ionic conductivity, high electrochemical stability) and desired mechanical properties of the non-ionic block through self-assembling nanophase separated structure (i.e., morphology), resulting in robust solid polymer electrolytes (SPEs). Ionic conductivity in PIL block copolymers is strongly influenced by morphology type, which was investigated exclusively to AB diblock copolymers. Compared to AB diblock copolymers, ABC triblock terpolymers offer access to more degrees of freedom, leading to not only three-phase analogues of morphologies observed in AB diblock copolymers but also a wide range of exotic morphologies. However, to date, the effect of the ion conducting block composition on the morphology and ionic conductivity of single-ion conducting ABC triblock terpolymers is yet to be explored.

In this work, we report the successful synthesis of 17 compositions of a poly(ionic liquid) (PIL) ABC triblock terpolymer, poly(S‑b‑VBMIm‑TFSI‑b‑HA) (S = styrene, VBMIm-TFSI = vinylbenzyl methylimidazolium bis(trifluoromethylsulfonyl)imide, HA = hexyl acrylate), via sequential reversible addition-fragmentation chain-transfer (RAFT) polymerization and post-polymerization modifications. A ternary morphology phase diagram was constructed and nine distinct morphologies were observed using small-angle X-ray scattering and transmission electron microscopy, including two-phase hexagonally packed cylinders, core-shell hexagonally packed cylinders, three-phase and two-phase lamellae, core-shell double gyroid, spheres-in-lamellae, and a three-phase hexagonal superlattice of cylinders. Morphology type significantly impacted the ion conductivity of the polymers, where remarkable changes in morphology factor (normalized ion conductivity) were observed with only small changes in the conducting volume fraction. An exceptionally high morphology factor of 2.0 was observed from the PIL ABC triblock terpolymer with a hexagonal superlattice morphology, attributed to the narrow, continuous PIL nanodomains that accelerate ion conduction. Overall, this work demonstrates the first systematic study of highly frustrated single-ion conducting ABC triblock terpolymers with a diverse set of morphologies and exceptionally high morphology factors, enabling the exploration of polymer architecture and ion transport relationships to guide the future design of highly conductive polymer electrolytes.