Bond strength regime dictates stress relaxation behavior

Reconfigurable polymer networks are gaining interest for their potential applications as self-healing, recyclable, and stimuli-responsive smart materials. Relating the bond strength of dynamic interactions to material properties including stress relaxation time and modulus is crucial for smart material design. In this work, in situ crosslinked transition metal-terpyridine reconfigurable networks were utilized to modulate the characteristic network stress relaxation time, τ R . The use of stress relaxation experiments rather than oscillatory frequency sweeps allowed for the measurement of network bond dynamics across a wider dynamic range than has been previously reported. The stress relaxation time was shown to be tunable by metal center, counterion, and crosslink density. Remarkably, the network crosslinked with covalent-like ruthenium chloride-terpyridine interaction, while having a longer τ R , was qualitatively similar to the other metal-ligand networks. Furthermore, the relaxation time was independent of crosslink density in strongly bonded networks, allowing for independent tunability of modulus and τ R . In contrast, increasing crosslink density reduced τ R in networks crosslinked with weaker interactions. This work utilizes in situ crosslinked dynamic networks to show differences in stress-relaxation behavior depending on the bond strength of the metal-ligand crosslinker used.