Novel cross-linking concept of polymer network: Synthesis, structure, and properties of slide-ring gels with freely movable junctions

We have recently developed a novel type of gel called the slide-ring gel or topological gel that is different from physical and chemical gels by using the supramoleculararchitecture with topological characteristics. In this gel, polymer chains with bulky end groups exhibit neither covalently cross-links as in chemical gels nor attractive interactions as in physical gels but are topologically interlocked by figure-of-eight cross-links. Hence, these cross-links can pass along the polymer chains freely to equalize the tension of the threading polymer chains similarly to pulleys; this is called the pulley effect. The slide-ring gel is a new cross-linking concept for the polymer network as well as a real example of a slip-link model or sliding gel, which was previously considered only theoretically. In this study, we review the synthesis, structure, and mechanical properties of the slide-ring gels with freely movable cross-linking junctions based primarily on our recent studies. The pulley effect of the slide-ring gels has been recently confirmed by mechanical measurements, small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), quasi-elastic light scattering (QELS), etc. This concept can be applied to not only gels but also to a wide variety of polymeric materials without solvents.