Emergence, evidence, and effect of junction clustering in supramolecular polymer materials

Abstract

A significant fraction of biomaterials consists of supramolecular polymers and networks formed by non-covalent interactions between associative motifs. They typically contain complex structures in which on top of binary associations, phase-separation and aggregation of associative junctions occur. Such hierarchical assemblies have significant influences on the dynamics as well as the physical and mechanical properties of the materials. Similar to supramolecular biomaterials, aggregation of associative junctions has also been frequently reported to occur in synthetic supramolecular polymers and networks. Engineering of such secondary structures in a sense to create and control the extent of hierarchical assemblies can be a powerful approach not only to alter the physical and mechanical properties of these materials but also to regulate novel functions like self-healing. To implement this approach, a deep knowledge about the physical origin of clusters and the subsequent manifestation in the properties and functions of the materials are required. To this end, we review a multitude of reports on the formation of hierarchical assemblies in supramolecular polymeric materials such as networks, thermoplastic elastomers, and gels. We classify motives for phase-separation and development of clusters and the possible subsequent hierarchical assemblies, as well as their influence on the materials’ physical and mechanical properties. We summarize the specific characterization methods and present selected example applications of supramolecular materials that operate based on such hierarchical structures. This overview proposes a high potential for designing supramolecular polymeric materials with tuned properties and specified functions based on the formation of clusters.