Polymer networks built out of dynamic covalent bonds offer the potential to translate the control and synthetic tunability of chemical reactions to macroscopic, physical properties. Hydrogels, a subset of polymer networks that are water-swollen and biocompatible, recapitulate viscoelastic features of natural tissues like stress relaxation when dynamic crosslinks are incorporated. We synthesized a series of dithiolalkylidene-based hydrogel crosslinks that undergo conjugate exchange with free thiols and demonstrated that the molecular exchange rates span four orders of magnitude. When incorporated into poly(ethylene glycol)-based hydrogels, this reactivity translated directly to the timescale of stress relaxation. Hirshfeld population analysis yielded a molecular descriptor that correlated with exchange rate and stress relaxation timescale, allowing for a quantitative structure-reactivity-property relationship to be developed. Using physical organic and computational insights to understand the basis for this differential reactivity, we designed a new crosslink structure to target an unobtained time regime. This work demonstrates the predictive potential of structure-reactivity-property relationships in covalent adaptable networks, which affords the opportunity to engineer new materials through mechanism-guided discovery and application of physical organic concepts.

Predictively tuning hydrogel viscoelasticity with structure-reactivity-property relationships

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