Controlling network relaxation and modulus with dynamic covalent chemistry and salt

Polymer networks with dynamic bonds are a promising route to sustainable materials, but many questions remain about the relationships between molecular structure and dynamics or mechanics. Dynamic polyethylene oxide (PEO) networks were prepared with two types of exchangeable bonds, one which coordinates to anions and one which coordinates to cations. In the former case, added LiTFSI salt leads to break up of the network and a corresponding drop in both modulus and viscosity. In the latter case, salt increases the modulus while decreasing the viscosity. Li NMR experiments reveal that depending on the length of PEO linkers in the network, the Li can either coordinate with ether oxygens or with the dynamic bond leading to vastly different dynamic mechanical properties even for the same polymer/dynamic bond/salt combination. In all cases, the moduli of the dynamic networks increase with temperature due to entropic elasticity, indicating the network topology is conserved even with salt addition. The environment preferred by the Li cations not only impacts the relaxation of the networks, but also can lead to conductivity when Li is solvated by PEO linkers. Our findings highlight the ability of dynamic chemistry and salt to work in tandem for designing recyclable functional polymers.