Hybrid Cross-Linking to Construct Functional Elastomers

ConspectusElastomers have been extensively used in diverse industrial sectors such as footwear, seals, tires, and cable jacketing and have attracted more and more attention in emerging fields such as regenerative medicine, soft robotics, and stretchable electronics. Global consumption of natural and synthetic elastomers amounted to nearly 27 million metric tons in 2020. In addition, to further enhance the common properties of elastomers, it is highly desired to endow elastomers with functionalities such as reprocessability, biomimetic mechanical properties, self-healing ability, bioactivity, and electrical conductivity, which will significantly broaden their applications. The covalent or noncovalent cross-linked structure is the essential factor for the elasticity of elastomers. Traditional elastomers usually comprise a single type of cross-linked molecular network, for which it is difficult to modulate the properties and introduce functionalities. Inspired by the simultaneous existence of multiple cross-linked structures in proteins, researchers have employed a hybrid cross-linking strategy to construct elastomers. Various noncovalent interactions (e.g., hydrogen bonds, metal-ligand coordination, ionic interactions, and chain folding) and dynamic covalent bonds (e.g., disulfide bonds, oxime-urethane bonds, and urea bonds) have been integrated in elastomers. Accordingly, the properties and functionalities of elastomers can be tuned by regulating the types, ratios, and distributions of cross-links. The hybrid cross-linking strategy provides a versatile and effective way to construct diverse functional elastomers for broad applications in various important fields.In this Account, we present our recent progress on functional elastomers constructed by a hybrid cross-linking strategy, including their design, preparation, properties, and diverse applications. First, we provide a brief introduction of the basic concept of functional elastomers and outline general strategies and mechanics for functional elastomers constructed by hybrid cross-linking. Then, we classify hybrid cross-linked elastomers by their design strategies, including multiple cross-linking, topological design, chemical coupling, and multiple networks. The relationships between the functionalities and hybrid cross-linked structures are summarized. At the same time, we also introduce diverse applications of these hybrid cross-linked elastomers in biomedicine, flexible electronics, soft robotics, 3D printing, and so on. Finally, we discuss our perspective on open challenges and future development trends of this rapidly evolving field. This Account highlighting the diverse hybrid cross-linked elastomers not only provides insights into strategies for elastomer functionalization but also provides new ideas for material design and inspires a variety of new applications.