Dynamic crosslinked rubbers for a green future: A material perspective

Conventional rubber products, such as tires, seals, tubing, and damping systems are manufactured via a vulcanization process, which forms covalently crosslinked network structures and ensures mechanical robustness, thermal stability and chemical resistance. However, the covalent networks are permanent and these products cannot be reprocessed or reshaped, which makes vulcanised rubbers one of the major challenges facing waste management and the circular economy. To reduce waste pollution for products such as tires, conventional vulcanised rubbers must be replaced with reversibly crosslinked structures which are able to achieve mechanical robustness and chemical stability, whilst also being able to be reprocessed, reshaped, reused and recycled. State-of-the-art developments in supramolecular chemistry have shed light on a new generation of reprocessable elastomers and rubbers, which have the potential to tackle the long-standing issue of waste tire pollution. The introduction of dynamic covalent bonds or supramolecular interactions in traditional elastomers can produce reversibly crosslinked structures, where the synergy between the dynamic bonds in the network are carefully optimised to balance the ease of processing, mechanical properties, and structural stability. Furthermore, dynamic covalent bonds and supramolecular interactions can provide ‘living’ functions to elastomers, such as self-healing and stimuli-responsiveness. These properties can be further enhanced by the addition of nanofillers with tailored surface chemistry to provide a dual role as a dynamic crosslinker and reinforcing element. To create reprocessable and recyclable elastomers, the coupling of multiple dynamic interactions provides unlimited possibilities to optimise the structure and properties of recyclable rubbers. Here we critically overview the applications of dynamic chemistry in rubbers, with a focus on macromolecular design and strategies to balance the mechanical, functional (e.g. self-healing) and reprocessing properties.