“Using dynamic covalent chemistry to control assembly, relaxation, and transport in polymer networks”
Dynamic covalent bonds incorporated into a polymer network can lead to materials which are capable of being recycled, dissolved back to monomer, and self-heal in response to damage. Dynamic bonds can also dramatically impact the relaxation, crystallization, and transport of small molecules through a polymer. I will first discuss networks with fast exchanging bonds where the viscoelasticity is probed over a broad (200 K) temperature window and shows a breakdown of classical Arrhenius behavior expected in these networks. These model networks reveal the role of crosslink density and molecular scale chemistry effects on macroscopic relaxation and dissipation. Next, semi-crystalline ethylene dynamic networks are investigated which exhibit very slow crystallization kinetics and distinct morphology relative to polyethylene, which is controlled by dynamic bond exchange. Finally, I will discuss the role of network architectures and bond exchange on the transport of ions or small molecules through polymers. Dense networks restrict diffusion, while dynamic bonds provide a mechanism to enhance transport. Adding salt to dynamic networks affects not only the conductivity, but can also lead to coordination with the dynamic bonds in the backbone giving rise to a rich interplay between the rheology and ion transport as a function of temperature. These studies point to the important roles of dynamic covalent chemistry on the fundamental properties of polymers for a range of applications.