Linking molecular structure to macroscopic rheology of dynamically associating polymer networks

Cross-linked polymer networks have long been used in materials applications, but dynamically cross-linked polymers have recently become more widespread. These dynamic cross-links, covering dynamic covalent bonds and transiently associating physical bonds, exhibit material properties that have led to advances in engineering from drug delivery to flexible electronics. We derived and experimentally validated a theory that describes a single polymer chain transiently binding to a viscoelastic background that is self-consistently solved from the initial chain. Polymers, such as hyaluronic acid, chemically modified with dynamically associating groups serve as model systems. We show that the theory links the molecular structure of these polymers to their macroscopic rheological properties and predicts rate constants for the dynamic bonds that follow the Arrhenius equation. The effective incorporation of a viscoelastic background composed of fluctuating, dynamic polymers indicates that the physical behavior of the environment and its fluctuations play an essential role in the dynamics and rheology of polymer networks. Understanding how environmental fluctuations affect the overall physical behavior is a general problem in soft matter and polymer physics.