Design of Highly Conductive PILs by Simple Modification of Poly(epichlorohydrin-co-ethylene oxide) with Monosubstituted Imidazoles

High ionic conductivity poly(ionic liquid)s (PILs) are of growing interest for their thermal and electrochemical stability, processability, and potential in safe, flexible all-solid-state electrochemical devices. While various approaches to enhance the ionic conductivity are reported, the influence of cation substituents is rarely addressed. Moreover, some of the asymmetric anions recently developed for high-conductivity ionic liquids were never tested in PILs. We report the design and synthesis of twelve novel cationic PILs prepared via quaternization of N-substituted imidazoles by commercially available poly(epichlorohydrin-co-ethylene oxide) (poly(EPCH-r-EO)) with subsequent ion metathesis. They differ by imidazolium side chain length (C1-C6 alkyl) and presence of heteroatoms (silyl, siloxane, and fluoroalkyl) and by anion type (bis(trifluoromethylsulfonyl)imide (TFSI), 2,2,2-trifluoromethylsulfonyl-N-cyanoamide (TFSAM), tetrafluoroborate (BF4), trifluoro(trifluoromethyl)borate (BF3CF3), and tricyanofluoroborate (BF(CN)3)). TFSI-based PILs with alkyl side chains gave lower glass transition temperatures (T g) and higher ionic conductivities than those bearing heteroatomic substituents, with n-butyl side chains providing a conductivity of 4.7 × 10-6 S cm-1 at 25 °C under anhydrous conditions. This increased to 1.0 × 10-5 and 4.5 × 10-4 S cm-1 at 25 and 70 °C, respectively, when the TFSI anion was replaced with BF(CN)3. All PILs showed good electrochemical (>3.2 V vs Ag+/Ag) and thermal (>185 °C) stability, making them excellent candidates for solid-state electrolytes in electrochemical devices.

Mechanically Robust Poly(ionic liquid) Block Copolymers as Self-Assembling Gating Materials for Single-Walled Carbon-Nanotube-Based Thin-Film Transistors

The proliferation of high-performance thin-film electronics depends on the development of highly conductive solid-state polymeric materials. We report on the synthesis and properties investigation of well-defined cationic and anionic poly(ionic liquid) AB-C type block copolymers, where the AB block was formed by random copolymerization of highly conductive anionic or cationic monomers with poly(ethylene glycol) methyl ether methacrylate, while the C block was obtained by post-polymerization of 2-phenylethyl methacrylate. The resulting ionic block copolymers were found to self-assemble into a lamellar morphology, exhibiting high ionic conductivity (up to 3.6 × 10^-6 S cm^-1 at 25 °C) and sufficient electrochemical stability (up to 3.4 V vs Ag⁺/Ag at 25 °C) as well as enhanced viscoelastic (mechanical) performance (storage modulus up to 3.8 × 10⁵ Pa). The polymers were then tested as separators in two all-solid-state electrochemical devices: parallel plate metal-insulator-metal (MIM) capacitors and thin-film transistors (TFTs). The laboratory-scale truly solid-state MIM capacitors showed the start of electrical double-layer (EDL) formation at ∼10³ Hz and high areal capacitance (up to 17.2 μF cm^-2). For solid-state TFTs, low hysteresis was observed at 10 Hz due to the completion of EDL formation and the devices were found to have low threshold voltages of -0.3 and 1.1 V for p-type and n-type operations, respectively.

New Pyridinium Type Poly(Ionic Liquids) as Membranes for CO₂ Separation

New pyridinium based PILs have been prepared by modification of their precursors based on high molecular weight aromatic polyethers bearing main chain pyridine units. The proposed methodology involves the conversion of the precursors to their ionic analogues via N-methylation reaction, followed by anion exchange methathesis reaction to result in PILs with the desirable anions (tetrafluoroborate and bis(trifluoromethylsulfonyl)imide). These PILs show excellent thermal stability, excellent mechanical properties, and most importantly can form very thin, free standing films with minimum thickness of 3 μm. As expected, the PIL containing the TFSI⁻ anion showed improved CO₂ and CH₄ permeabilities compared to its analogue containing the BF₄⁻. PIL-IL composites membranes have also been prepared using the same PIL and different percentages of pyridinium based IL where it was shown that the membrane with the highest IL weight percentage (45 wt %) showed the highest CO₂ permeability (11.8 Barrer) and a high CO₂/CH₄ ideal selectivity of 35 at room temperature.

Recent advances in alkyne-based click polymerizations

The recent progress in alkyne-based click polymerizations and their application in the preparation of new functional polymers are summarized. The challenges and opportunities in this area are also briefly discussed.