Ion Conducting ROMP Monomers Based on (Oxa)norbornenes with Pendant Imidazolium Salts Connected via Oligo(oxyethylene) Units and with Oligo(ethyleneoxy) Terminal Moieties

Abstract

A matrix of 22 two-armed norbornene-based imidazolium TFSI monomers (8) was synthesized to determine the optimal structure in terms of single ion conductivity. For the chain tethering the imidazolium ring to the norbornene ring three or four oxyethylene units are optimal. A terminal group of two ethyleneoxy units was optimal. NMR studies indicated that both the tether oxyethylene units and the terminal ethyleneoxy units interact with the imidazolium cation via hydrogen bonding. 8r (X = 4, Y = 2) exhibited a conductivity of 9.57 × 10–5 S/cm at 25 °C and a T g of −46 °C. Low T g values do not correlate with higher conductivity as a result of the H-bonding interactions. Stability toward autopolymerization and reasonable conductivities provide an acceptable platform for ion conducting ROMP polymers. Four one-armed norbornene-based imidazolium TFSI monomers (15) were prepared with tetra­(ethyleneoxy) linkers/spacers and variable terminal groups. All of these exhibited low T gs (<−55 °C) and room temperature conductivities >10–4 S/cm, the highest being 4.39 × 10–4 S/cm for 15c (T g = −69 °C), the analogue of 8r, providing hope for outstanding polymers. Three oxanorbornene-based two-armed imidazolium TFSI monomers (18) were prepared with varied linkers and terminal groups. 18b possesses a room temperature conductivity of 1.2 × 10–4 S/cm, again augering well for polymers derived therefrom by ROMP.

The Effect of Oligo(oxyethylene) Moieties on Ion Conduction and Dielectric Properties of Norbornene-Based Imidazolium Tf2N Ionic Liquid Monomers

“…46 These studies of ion and polymer dynamics are also complemented by linear viscoelastic studies using oscillatory shear. The detailed preparations of these monomers and their stereochemistry (confirming the stereo purity of the exo products in all the ILMs studied) were described in an earlier study 39 and summarized in the Supporting Information.…”

“…69,70 This intramolecular interaction is supported by the observation from 1 H NMR studies, indicating the tether (spacer) OE and terminal EO segments interact with the imidazolium cation via hydrogen bonding. 39 Such H−O ether interactions allow for a reduction of Im + Tf 2 N − pair dissociation energy, effectively stabilizing the anion separated from the cation. 17 The stable complexes among the Im + , Tf 2 N − , OE, and EO presumably not only push the quadrupoles (Im + Tf 2 N − ) 2 , having no dipole moment, to be separated into ion pairs (Im + Tf 2 N − ), which contributes to an increase of the number density of dipoles, but also increase the average distance between Im + and Tf 2 N − of ion pairs, which contributes to an enhanced dipole moment of the average ion pair, compared to the contact ion pairs.…”

“…Figure 1 displays the chemical structures of five norbornene-based Im + Tf 2 N − ILMs [termed M_D (or S)_C 2 OE x ImEO y , where M = monomer, D = double, S = single, C 2 = (CH 2 ) 2 , OE = oxyethylene, Im = imidazolium, and EO = ethyleneoxy].The detailed preparations of these monomers and their stereochemistry (confirming the stereo purity of the exo products in all the ILMs studied) were described in an earlier study39 and summarized in the Supporting Information.2.1. Linear Viscoelasticity (LVE).…”

“…Recently, we reported a series of new imidazolium-based norbornene diester ILMs having double imidazolium (= Im + ) (CF 3 SO 2 ) 2 N – (= Tf 2 N – ) (termed Im + Tf 2 N – ) arms as pendants containing either alkylene [(CH 2 ) 2 ] or oxyethylene [(OCH 2 CH 2 ) x = (OE) x , x = 1, 2 or 3] units as linkers between the norbornene moiety and the imidazolium cation and their PILs, via ring-opening metathesis polymerization (ROMP). , Although there have been a few studies of PILs based on single-arm polynorbornenes for self-healing materials , and conducting polymer electrolytes, − the conduction mechanism in norbornene-based ILMs and PILs with double-arm geometries is far from being fully understood. The focus of the current investigation is therefore to explore molecular parameters that control the ionic conductivity of norbornene double imidazolium-based ILMs, while a full report on the dynamics of the corresponding PILs will comprise a forthcoming publication.…”

“…Figure 1. Chemical structures of norbornene-based double (or single) Im + Tf 2 N − ionic liquid monomers with different linker types Z and tails R (M_D_C 2 ImEO 2 , M_D_C 2 OEImEO 2 , M_D_C 2 OE 2 ImEO 2 , M_D_C 2 OE 3 ImEO 2 , and M_S_C 2 OE 3 ImEO 2 ) 39. …”