Understanding the role of dynamic bonds on conductivity in dense polymer networks

We have investigated a series of ethylene oxide networks containing a range of permanent and dynamic crosslinks to understand the role of bond exchange on conductivity. All systems are studied with added LiTFSI salt, and in the case of permanent networks a suppression in conduction is observed as the mesh size decreases. Next, electrolytes with dynamic boronic ester bonds (which exchange in a topology conserving manner) were synthesized which show a massive drop in modulus and stress relaxation times with salt addition, attributed to boron-anion interactions. Analogous networks were also prepared with a slower exchanging dynamic bond (vinylogous urethane) which show a similar drop in stress relaxation times, but essentially unchanged modulus with salt addition. In all cases, an optimal conductivity is observed with added salt before aggregation occurs. This work shows the distinct responses which can be achieved in dynamic network electrolytes, and how modulus can be decoupled from viscosity in ionic materials.