Advancing macromolecular hoop construction: recent developments in synthetic cyclic polymer chemistry

The exploration of macromolecular topology provides common ground amongst chemists, material scientists, mathematicians, and artists. Fascinating polymer architectures, ranging from linear to branched to cyclic to star, can be constructed from myriad building blocks; their topological-dependent properties merge the beauty of symmetry with the intricacies of polymer physics. Specifically in cyclic macromolecules, the lack of chain ends result in unique physical characteristics ( e.g. , smaller hydrodynamics volume, lower viscosity, and lack of chain entanglement) compared to their linear counterparts. In this review, developments in the synthesis of cyclic polymers will be addressed, with an emphasis of recent advances in the past five years. Synthetic methodology to access cyclic macromolecules continues to develop via two distinct mechanistic classes: ring-expansion of macrocyclic initiators and ring-closure of functionalized linear polymers.