A review of rheology for ring polymers and polymers with internal loops: comparison of recent experimental and theoretical studies

Polymer architecture (i.e., chain connecting manner) and properties are closely correlate, and strongly influence rheological properties that reflect microscopic molecular dynamics. This review summarizes the rheological properties of ring polymers and polymers containing intramolecular loops, which are currently being studied actively in terms of sample synthesis and physical property. The ring polymers, which have a well-defined molecular architecture and free of impurities, exhibit rheological properties that differ significantly from those of their linear counterparts. Notably, even minor contamination with linear chain impurities is known to substantially alter the rheological properties of ring polymers. Theoretical molecular modeling studies are being pursed to elucidate these behaviors. The ring polymer analogues consisting of multiple ring chains or intramolecular linkages between ring and linear chains exhibit either unentangled or intermolecular penetration behavior, depending on their molecular architectures. The polymers featuring intrinsically random intramolecular loops, such as single-chain polymeric nanoparticles (SCNPs) and polymeric nanosheets, are also under active investigation in terms of both their synthesis and properties. A deeper understanding of the molecular dynamics and rheological properties of these unique architectural polymers can contribute to the further development of polymer science and industry as well as to the creation of new polymeric nano-materials.