Topological gel: A third kind of gel consisting of linear polymer chains and figure-of-eight cross-links

Topological gel is a new kind of gel synthesized from the polyrotaxanes in which a PEG or PEO chain with large molecular weight is surrounded by a few α-cyclodextrins (α-CD). By chemically cross-linking the α-CD contained in the polyrotaxanes in solutions, transparent gels with good tensibility and large swellability could be realized. In this gel, the polymer chains with bulky end groups are neither covalently cross-linked like chemical gels nor attractively interacted like physical gels, but are topologically interlocked by figure-of-eight cross-links. Therefore, the polymer chains freely pass through the cross-links acting like pulleys, which is supposed to automatically equalize the nanoscopic heterogeneity in structure and stress. In this study, the elastic properties of the topological gel were investigated from both experiments and theory based on the pulley effect. Then, some sliding motion of α-CD in the topological gel was observed by using dynamic light scattering. Finally, a topological gel which swells by 24000 times the dry weight was produced.