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) , lower intrinsic viscosity , high critical solution temperature , accelerated rate of crystallization , and high refractive indices . 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.
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A.T. is grateful for financial support from the Ministry of Education, Science and Culture of Japan (Grant-in-Aid for Development Scientific Research 18K19112 and 20H02786). Y.M. also acknowledges Dr. Mikihiro Hayashi and Prof. Masahiro Higuchi for their fruitful discussions and technical assistance.
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Muramatsu, Y., Takasu, A. Synthetic innovations for cyclic polymers. Polym J 54, 121–132 (2022). https://doi.org/10.1038/s41428-021-00560-5