Role of Tethered Ion Placement on Polymerized Ionic Liquid Structure and Conductivity: Pendant versus Backbone Charge Placement

Abstract

The role of ion placement was systematically investigated in imidazolium bis­(trifluoromethane)­sulfonimide (ImTFSI) polymerized ionic liquids (PILs) containing pendant charges and charges in the backbone (sometimes called ionenes). The backbone PILs were synthesized via a facile step growth route, and pendant PILs were synthesized via RAFT. Both PILs were designed to have nearly identical charge density, and the conductivity was found to be substantially enhanced in the backbone PIL systems even after accounting for differences in the glass transition temperature (T g). Wide-angle X-ray scattering (WAXS) revealed an invariance in the location of the amorphous halo between the two systems, while the anion–anion correlation peak was shifted to lower scattering wavevector (q) in the backbone PILs. This indicates an increase in the correlation length of ions and is consistent with charge transport along a more correlated pathway following the polymer backbone. Due to the linear nature of the backbone PILs, crystallization was observed and correlated with changes in conductivity. Upon crystallization, the conductivity dropped, and eventually, two populations of mobile ions were observed and attributed to ions in the amorphous and near-crystallite regions. The present work demonstrates the important role of ion placement on local structure and conductivity as well as the ability of backbone PILs to be used as controllable optical or dielectric materials based on crystallization or processing history.

Recent Advances in the Design of Ionenes: Toward Convergence with High‐Performance Polymers

“…Cationic ionenes are typically synthesized via the Menshutkin reaction, where “A‐A + B‐B” condensation polymerizations occur between 3 o diamines and dihalides (or other electrophiles with similar reactivity), resulting in covalently tethered chains of cations . Pyridine, phosphine, imidazole, and triazole compounds have also been used in place of diamines to respectively form pyridinium, phosphonium, imidazolium, and triazolium ionenes.…”

“…Imidazolium‐ and phosphonium‐based ionenes have been identified as likely to exhibit much better thermal stability . Segalman's group has directly compared poly(IL) and ionene architectures in terms of their ion conductivity and nanostructure, noting that the ionene configuration enhances ion mobility and was much more ordered …”

Ion Transport in Dynamic Polymer Networks Based on Metal–Ligand Coordination: Effect of Cross-Linker Concentration

“…This observation is consistent with that reported for chemically crosslinked ion-conducting networks generated from copolymerization of ionic liquid monomers with varying contents of multi-functional crosslinkers, 59 and polymer electrolytes based on PEO and LiNTf2. 51 Although the complexation of Ni 2+ by imidazole moieties couples ion transport to the polymer segmental dynamics, this does not translate into a single NTf2 -conductor, such as polymerized ionic liquids based on imidazolium, [33][34][35][36][37][38][39] as the kinetically labile nature of metal-ligand coordination bonds allows for bond breakage and formation on time scales that could facilitate long-range Ni 2+ transport as long as the operating temperature is above Tg. A more quantitative relationship between ion content and mobility is currently under investigation and outside the scope of this work.…”

Syntheses, characterizations and functions of cationic polyethers with imidazolium-based ionic liquid moieties

“…[5][6][7] The synthesis and properties of poly(IL)s have been extensively studied in the past two decades, and now it is established as an emerging field in chemistry. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] The development of poly(IL)s not only allowed combining the unique properties of ionic liquids with the processability and solidity of polymer materials, but also allowed for the attainment of new functions. There are two basic methods to synthesize poly(IL)s. One is the direct polymerization of ionic liquid monomers, and the other is the quaternization of existing polymer materials.…”