Dynamically Cross-Linked Waterborne Polyurethanes: Transalkylation Exchange of C-N Bonds Toward High Performance and Reprocessable Thermosets

Thermosetting waterborne polyurethanes (WPUs) have received wide attention because of their excellent chemical resistance, mechanical properties, and low water absorption. However, their permanent network structure hinders their reprocessing applications, making it vital to prepare reprocessable thermosetting WPUs to minimize plastic pollution. Herein, for the first time, the cross-linked WPUs with excellent reprocessability were designed and synthesized by introducing covalent adaptable networks (CANs) in the form of quaternary ammonium alkyl chains. Our methodology combined CO2-triggered WPUs (CO2-triggered WPUs) with 1,6-diiodohexane. After the CO2 evaporated during film formation, the CO2-triggered WPUs left tertiary amine groups as reaction precursors, which could cross-link into a WPU CAN with 1,6-diiodohexane. All cross-linked WPUs possessed classic vitrimer performance including stress relaxation and malleability, as confirmed by stress-relaxation and hot-press tests. The results showed that cross-linked WPUs had excellent reprocessability and high mechanical properties, and the recovery ratios of the mechanical properties for the recycled samples were over 80% and the tensile strength was more than 17 MPa. More importantly, the cross-linked WPUs' antibacterial rates of Staphylococcus aureus and Escherichia coli were 94.3 and 89.5%, respectively. This research offers a new method to synthesize high-performance WPUs via facile quaternary ammonium reversible cross-linking and demonstrates that WPU CANs have great potential as sustainable materials.

Automated summary

This study presents the design and synthesis of cross-linked thermosetting waterborne polyurethanes (WPUs) with excellent reprocessability. The cross-linked WPUs exhibit classic vitrimer performance and high mechanical properties, with a recovery ratio of over 80% for the recycled samples. Moreover, the cross-linked WPUs show significant antibacterial activity. This research provides a new method for the reprocessing of thermosetting WPUs and demonstrates the potential of WPU CANs as sustainable materials.