A Water-Free Ionic Covalent Organic Polymer with High Electrorheological Activity and Temperature Stability

Ionic polymers are important electrorheological (ER) materials, whose ER effect originates from ion motion-induced interfacial polarization. However, the first-generation ionic polymer ER material based on traditional polyelectrolyte needs adsorbed water to make ion movement to activate the ER effect. This results in poor temperature and cycling stability. Although the second-generation ionic polymer ER material based on polyethylene oxide-salt complexes and the currently developed poly(ionic liquid) ER material do not require adsorption of water to activate the ER effect due to decreased ion-pair dissociation energy, low glass transition temperature still limits their temperature and cycling stability. Herein, we report an ionic polymer ER material based on ionic covalent organic polymer (iCOP) synthesized via the Menshutkin reaction and ion exchange, which exhibits not only a highly anhydrous ER effect due to lots of hydrophobic fluoric counterion-induced strong interfacial polarization but also excellent temperature stability and cycling stability due to a unique covalent organic framework structure. In particular, its leaking current density and power consumption are far lower than those of the ER system of traditional polyelectrolytes, polyethylene oxide-salt complexes, and poly(ionic liquid)s. These make iCOP possess large potential as a platform to develop next-generation ionic polymer ER material with high performance.