Recently, Prof. Wang Xu's group from the National Engineering Research Center for Colloidal Materials of Shandong University has achieved a significant breakthrough in the development of ultra tough and reversibly cross-linked polymer networks. Addressing the challenge of combining high mechanical performance with reprocessability in thermosetting materials, The Wang group has employed mismatched supramolecular units to precisely engineer the molecular structure of thermoset elastomers. This strategy not only enhances the strength and toughness of the materials while maintaining their thermosetting properties but also significantly improves their multi-recyclability. This result was published on Advanced Materials(IF = 29.4) with the title "Mismatched Supramolecular Interactions Facilitate the Reprocessing of Super-Strong and Ultratough Thermoset Elastomers". Prof. Wang Xu is the corresponding author, with PhD candidate Wang Luping as the first author, and Shandong University is the first author unit and the corresponding author unit.

Thermosetting polymer materials play key roles in the modern plastics and rubber industries, accounting for a global annual production exceeding 65 million tons. Thermosetting materials frequently have benefits including insolubility, non-melting characteristics, and mechanical stability because of their distinct covalently cross-linked network structures. However, this high cross-linking density restricts the tensile performance and recyclability of the material. These restrictions obstruct the advancement of the circular economy and the sustainable development of thermosetting materials.

To address these issues, the incorporation of dynamic covalent or noncovalent bonds into polymer networks has been examined, as has chemical upcycling. However, as the mechanical properties of thermosetting materials are improved, they become more difficult to recycle. The development of multi-recyclable thermosetting materials with high strength and toughness characteristics therefore remains challenging. Undoubtedly, these advancements could significantly aid the growth of numerous industries and hold the potential to mitigate environmental pollution levels as well.

Figure 1. Schematic of the structure-property relationship of SPUUN-IE elastomer

This work introduces mismatched supramolecular units into a covalently cross-linked poly (urethane-urea)network containing dynamic acyl semicarbazide (ASC) moieties. By forming mismatched supramolecular interactions (MMSIs), the energy dissipation capacity and dynamics of the covalently cross-linked network are modulated. The optimized thermoset elastomer (SPUUN-IE), was found to exhibit an unprecedented tensile toughness of1245.2 MJ m⁻³, an ultrahigh ultimate engineering stress of 110.8 MPa, and a significant resistance to chemical media, creep, and damage. More importantly, it was possible to reprocess the SPUUN-IE specimen at least four times with an extremely high recycling efficiency (close to 100%). The value of tensile toughness of this thermoset elastomer with MMSIsoutperforms all thermoset elastomers reported to date. Compared to the thermoset elastomers containing matched supramolecular interactions (MSIs), it has milder recycling conditions and a 2.7-fold increase in recycling efficiency.

Figure 2.Comparison between MMSIs and MSIs

This simple and efficient approach promotes the development of thermosetting materials with high mechanical performance and recyclability, offering new possibilities for the recyclability and reuse of thermosetting materials in various industrial fields.

The group's goal is to support sustainable development through controlled synthesis and the study of the structure-property relationship of sustainable supramolecular polymers. Related research papers have been published in journals like Angew. Chem. Int. Ed., Adv. Mater., and CCS Chem., demonstrating their considerable progress. Additionally, they have authorized 12 invention patents, some of which have been effectively converted into practical applications.

The study was financially supported by the Natural Science Foundation of Shandong Province and the National Natural Science Foundation of China.

Link to the paper: https://onlinelibrary.wiley.com/doi/10.1002/adma.202311758