The Role of Hydrogen Bonding in the Formation and Dynamics of Two Distinct Types of Cyclic Supramolecular Polymers

Cyclic polymers are attractive synthetic targets in both polymer chemistry and supramolecular polymer (SP) chemistry; however, there is a gap between these two research fields in terms of the synthetic strategies involved, and achieving a commonality remains elusive. Herein, we describe the formation of two distinct types of cyclic SPs from structurally similar rosette-shaped molecules. The first SP (Type I) is characterized by a uniform diameter and circularity, whereas the other (Type II) has properties reminiscent of flexible cyclic covalent polymers. Remarkably, the only difference in the structures of the two monomers that form these completely distinct cyclic SPs is the absence (Type I) or presence (Type II) of hydrogen-bonding moieties. An all-atom molecular-dynamics simulation suggested that the Type II SP can adopt various "conformations" due to the dynamic nature of its hydrogen bonds, thereby behaving like a flexible covalent polymer. Real-time high-speed atomic-force microscopy (AFM) confirmed the presence of flexibility in the chains of the Type II SP on the observation timescale (several tens of seconds). Our results therefore highlight an example of a similarity between a covalent polymer and a noncovalent SP that should help to bridge the gap between these polymers, leading to new advanced materials.