Dynamic covalent bonds are frequently incorporated into polymer networks to impart recyclability and self-healing into intractable materials. Our group uses dynamic covalent bonds to impart additional functionality by leveraging bond exchange to design the complex viscoelasticity of polymer networks as well as control small molecule transport. While the modulus is simply controlled by crosslink density, the relaxation of the networks can be dramatically tuned over at least five orders of magnitude via dynamic bond selection. In neutral dynamic networks, we have shown that topology conserving bond exchange leads to an increase in modulus with heating, while dissociative bonds lead to softening. This allows for exquisite control over the full viscoelastic response of the material and presents a powerful platform for soft materials design. Salt addition is another route to modulate viscoelasticity through the coordination of various dynamic bonds with the anion (boronic esters) or the cation (vinylogous urethanes). In both cases, the salt counterintuitively decreases the viscosity, while the modulus may be maintained or decrease depending on the precise interaction between bond and ion. Salt also imparts conductivity, and our group has pioneered efforts in dynamic network electrolytes which are conductive, self-healing, and recyclable back to monomer while connecting the observed ion transport to molecular aspects of the network. Dynamic bond are also a powerful tool for precise control of neutral molecule transport, a key aspect of low energy passive membranes. When the topology is conserved (vitrimers), the effect of network confinement on molecular diffusion is the same between permanent and dynamic networks. Conversely, at a given temperature with respect to the glass temperature, dynamic networks show substantially faster diffusion coefficients relative to permanent analogous. Dynamic bonds in polymer networks serve as a powerful and general route to control conductivity, transport, viscosity, and modulus through molecular design considerations.

Leveraging dynamic covalent bonds for precise viscoelastic design and highly selective control of mass and ion transport in polymer networks

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.