Ion Conducting ROMP Monomers Based on (Oxa)norbornenes with Pendant Imidazolium Salts Connected via Oligo(oxyethylene) Units and with Oligo(ethyleneoxy) Terminal Moieties
2019-02-08T19:13:13Z (GMT) by
A matrix of 22 two-armed norbornene-based imidazolium TFSI monomers (<b>8</b>) 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. <b>8r</b> (<i>X</i> = 4, <i>Y</i> = 2) exhibited a conductivity of 9.57 × 10<sup>–5</sup> S/cm at 25 °C and a <i>T</i><sub>g</sub> of −46 °C. Low <i>T</i><sub>g</sub> 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 (<b>15</b>) were prepared with tetra(ethyleneoxy) linkers/spacers and variable terminal groups. All of these exhibited low <i>T</i><sub>g</sub>s (<−55 °C) and room temperature conductivities >10<sup>–4</sup> S/cm, the highest being 4.39 × 10<sup>–4</sup> S/cm for <b>15c</b> (<i>T</i><sub>g</sub> = −69 °C), the analogue of <b>8r</b>, providing hope for outstanding polymers. Three oxanorbornene-based two-armed imidazolium TFSI monomers (<b>18</b>) were prepared with varied linkers and terminal groups. <b>18b</b> possesses a room temperature conductivity of 1.2 × 10<sup>–4</sup> S/cm, again augering well for polymers derived therefrom by ROMP.