Self-Healing Glass Constructed from Oligo(thiourea) Macrocycles

The topological architecture of molecules can strongly influence the macroscopic properties of materials. However, compared with classical molecular parameters such as molecular weight, molecular-weight distribution, and end- or side-group modification, topological effects in polymer materials remain insufficiently explored, especially in functional systems. No self-healing material composed solely of cyclic molecules has yet been reported, and a systematic comparison between cyclic and linear topologies in self-healing materials is still lacking. Because conventional self-healing is generally associated with the reorganization of polymer-chain entanglements, whereas cyclic topology suppresses entanglement, whether cyclic molecules can form room-temperature self-healing materials has remained unresolved.

In 2018, our group developed poly(thiourea-ether), the first polymer capable of self-healing at room temperature below its glass-transition temperature. Building on this platform, we show that a cyclic thiourea hexamer, despite lacking end groups and chain entanglements, exhibits room-temperature glassy self-healing comparable to its linear polymer analogue while maintaining high thermal and mechanical stability. By contrast, linear oligomers of the same molecular weight lose mechanical strength and are no longer glassy at room temperature. Systematic analyses of hydrogen-bonding structure, molecular conformation, and relaxation dynamics reveal that ring topology governs the reconfigurability, self-healing behavior, and mechanical stability of the glassy state. These results establish molecular topology as an effective design parameter for glassy materials and provide an experimentally testable strategy for developing self-healing and amorphous materials through topological regulation.