Hassel and Marianne Ledbetter MatSE Colloquium - "Connecting dynamic processes in covalent adaptable polymer networks from monomer-scale to bulk"

Dynamic covalent bonds in polymer networks have shown great promise for imparting recyclability into otherwise intractable thermosets and elastomers. They can also enhance the performance of damping materials, self-healing coatings, and membranes via exchange of networks strands. Recently, our group has pursued a quantitative understanding of how bond exchange controls the complex viscoelasticity of polymer networks spanning from the glassy response to liquid-like flow. For a fixed polymer backbone, networks with dynamic bonds spanning five orders of magnitude in exchange rates have been investigated to quantify how modulus, exchange times, monomer scale dynamics, and bulk relaxation times are governed by the underlying chemistry. Quantitative agreement between models and experiment are obtained, and allow for better predictive design of polymer viscoelasticity. Bond exchange is also shown to provide local mobility for diffusion of probe molecules depending on the exchange kinetics, mesh size and penetrant diameter which provides a mechanism for selective separations. Finally, the presence of two kinetically distinct dynamic crosslinks in a single network has revealed key insights on how multiple energy dissipating relaxation processes can arise with depending on architecture and exchange mechanism.