Synthetic innovations for cyclic polymers

The relationship between the primary structures of polymers and their properties has long been recognized as an important research subject for polymer chemists. Advanced chemical procedures allowing precise control of the structure also enable us to examine the topological effects on polymer properties. Cyclic polymers possess unique characteristics due to the absence of polymer termini, showing different bulk and solution properties from their corresponding linear counterparts, i.e., smaller hydrodynamic volume and radius of gyration (Rg) [1], lower intrinsic viscosity [2], high critical solution temperature [2], accelerated rate of crystallization [3], and high refractive indices [4]. To make progress in this research field, innovative synthetic procedures are essential. The synthetic strategy for cyclic polymers has two typical pathways: the ring closure of functional linear polymers and ring expansion polymerization using cyclic monomers, an initiator, or a catalyst. This review describes the recent synthetic evolution of cyclic polymers, focusing on our new strategy: ring closing without highly dilute conditions. Relationship between the primary structures and their properties is recognized as an important research subject for polymer chemists. To make progress in this academic field, innovative synthetic procedures of cyclic polymers are essential. The synthetic strategy has two typical pathways: one is the ring closure of functional linear polymers and the other is ring expansion polymerization using cyclic monomers, an initiator, or a catalyst. This focus review deals with the recent synthetic evolution of cyclic polymers, focusing on our new strategy: ring closing without highly dilute conditions.