(181bc) ABC Polymeric Ionic Liquid Triblock Terpolymers

Polymeric ionic liquid (PIL) block copolymers are a distinct set of block copolymers that incorporate the unique physiochemical properties of PILs (e.g., high solid-state ionic conductivity, high chemical, thermal and electrochemical stability, and widely tunable physical properties) into block copolymer architecture, which allows for self-assembly into a range of nanostructures where morphology type and domain size are tunable. Recently, PIL block copolymers have been synthesized by several research groups and have shown to possess distinct conductivity-morphology relationships that have now impacted several applications, e.g., batteries, fuel cells.¹ However, almost all reports are exclusive to (AB) diblock copolymers.Although AB diblock copolymers can provide orthogonal properties of high ion conduction and high mechanical strength in a solid-state material, there are limitations to AB diblock copolymers, such as a limited set of morphologies, domain sizes, and the lack of a means to achieve a combination of more than two properties simultaneously (e.g., conductivity, strength, flexibility). Moreover, spatially connected 3D network morphologies, which often result in the highest ion conductivities, occur only over a small compositional range in AB diblock copolymers. Compared to AB diblock copolymers, multiblock polymers (e.g., ABC) produce more morphology types, more 3D network morphology types, and a broader composition range to achieve 3D network morphologies.

In this study, an ABC PIL triblock terpolymer was synthesized to explore a PIL-containing polymer with a richer compliment of properties, a wider diversity of cation/backbone chemistries, and a broader compositional range to obtain a variety of continuous 3D network morphologies. Specifically, poly(S-b-VBMPyr-TFSI-b-HMA)was synthesized viasequential reversible addition-fragmentation chain-transfer (RAFT) polymerization and subsequently quaternized, where A block = styrene (S), B block or PIL block = vinylbenzyl methylpyrrilidonium bis(trifluoromethylsulfonyl)imide(VBMPyr-TFSI), and C block = hexyl methacrylate (HMA). Reaction kinetics of this PIL ABC triblock terpolymer were investigated and these results were utilized in scaling up the polymerization reaction to > 200 g quantities with narrow polydispersities and controllable block compositions. Chemical, thermal, morphological, and ion conductive properties were characterized using ¹H nuclear magnetic resonance (NMR) spectroscopy, elemental analysis (EA), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and electrical impedance spectroscopy (EIS).

1. Meek, K. M.; Elabd, Y. A., Polymerized ionic liquid block copolymers for electrochemical energy. J Mater Chem A 2015, 3(48), 24187-24194.