Megasupramolecules take to water

To mimic the valuable rheological effects of dilute ultralong polymers (e.g.,5×10⁶g/mol) without the limitations imposed by flow-induced chain scission, we examine pair-wise end association of “unimers” (ca. 8×10⁵g/mol) to form “megasupramolecules.” Here, we examine an aqueous system using polyacrylamide with terpyridine ends (TPAM) as the unimers and metal-ligand association with nickel (Ni²⁺) to link them end-to-end. Their slow end-exchange dynamics enables highly non-equilibrium distributions of megasupramolecules to be produced by varying the sample preparation protocol. The resulting metastable distributions of supramolecules are sufficiently long lived that they can be analyzed by size-exclusion chromatography (SEC) and dripping onto substrate extensional rheometry (DoSER). By varying the preparation protocol and Ni²⁺ concentration, while holding polymer structure and polymer concentration fixed, different distributions of megasupramolecules are produced that span more than a decade of extensional relaxation time. Hypotheses and unanswered questions regarding the distributions of supramolecular topology and molecular weight and the resulting extensional flow behavior will be presented.