(649f) Targeted Synthesis of 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 the self-assembled nanostructure of block copolymers. Ionic conductivity in PIL block copolymers, a property of interest for batteries and fuel cells, is strongly influenced by morphology type.¹ Although PIL block copolymers have been investigated by several research groups,² most reports are exclusive to AB diblock copolymers, which are limited to few morphology types. Moreover, the spatially connected 3D network morphology, which exhibits the highest ionic conductivity, occurs over a small compositional range in AB diblock copolymers. Compared to AB diblock copolymers, ABC triblock terpolymers can potentially exhibit many more morphologies (70+), as well as many 3D network morphologies, which occur over a larger composition range.³ To date, there are limited reports on PIL ABC triblock terpolymers and their synthesis is complex, requiring three polymerization steps, followed by quaternization of a PIL precursor, followed by ion exchange to the final desired counter anion form. In order to study composition-morphology-conductivity relationships in PIL ABC triblock terpolymers, a targeted synthesis approach to produce compositions that result in 3D network morphologies is desired.

In this work, targeted synthesis of specific compositions of a novel PIL ABC triblock terpolymer was scaled up to quantities that would allow for adequate materials characterization by numerous techniques. Specifically, a set of multiple compositions of poly(S-b-VBMPyr-TFSI-b-HA) were synthesized via sequential reversible addition-fragmentation chain-transfer (RAFT) polymerization and subsequently quaternized, where A block = styrene (S), B block or PIL block = vinylbenzyl methylimidazolium bis(trifluoromethylsulfonyl)imide (VBMIm-TFSI), and C block = hexyl acrylate (HA). Large-scale reflux reactions (>500 mL reacting mixture) produced the first block at a 300 g product scale followed by chain extension reactions at 100 g and 20 g product scales for the diblock and triblock reactions, respectively. A polymerization model was developed and combined with experiments (in situ ¹H NMR spectroscopy small-scale reaction kinetic polymerization data) to guide the larger scale targeted synthesis of PIL ABC triblock terpolymers at desired compositions.⁴ Successful targeted synthesis at specific compositions will enable the future exploration of composition-morphology-conductivity relationships in PIL ABC triblock terpolymers.

1. Choi, J. H.; Ye, Y. S.; Elabd, Y. A.; Winey, K. I., Network Structure and Strong Microphase Separation for High Ion Conductivity in Polymerized Ionic Liquid Block Copolymers. Macromolecules 2013, 46 (13), 5290-5300.
2. Meek, K. M.; Elabd, Y. A., Polymerized ionic liquid block copolymers for electrochemical energy. J Mater Chem A 2015, 3 (48), 24187-24194.
3. Epps, T. H.; Cochran, E. W.; Hardy, C. M.; Bailey, T. S.; Waletzko, R. S.; Bates, F. S., Network phases in ABC triblock copolymers. Macromolecules 2004, 37 (19), 7085-7088.
4. Lathrop, P. M.; Duan, Z. Y.; Ling, C.; Elabd, Y. A.; Kravaris, C., Modeling and Observer-Based Monitoring of RAFT Homopolymerization Reactions. Processes 2019, 7 (10).