Tough and Multi-Recyclable Cross-Linked Supramolecular Polyureas via Incorporating Noncovalent Bonds into Main-Chains

Covalent thermosets generally exhibit robust mechanical properties, while they are fragile and lack the ability to be reprocessed or recycled. Herein, a new strategy of incorporating noncovalent bonds into main-chains is developed to construct tough and multi-recyclable cross-linked supramolecular polyureas (CSPU), which are prepared via the copolymerization of diisocyanate monomers, noncovalently bonded diamine monomers linked by quadruple hydrogen bonds, and covalent diamine/triamine monomers. The CSPU exhibit remarkable solvent resistance and outstanding mechanical properties owing to the covalent cross-linking via triamine monomer. Through the incorporation of 9.7% and 14.6% quadruple hydrogen bonded diamine monomer, the transparent CSPU films are endowed with superior toughness of 74.17 and 124.17 MJ m⁻³, respectively. Impressively, even after five generations of recycling processes, the mechanical properties of reprocessed CSPU can recover more than 95% of their original properties, displaying excellent multiple recyclablity. As a result, the superior toughness, remarkable solvent resistance, high transparency, and excellent multiple recyclability are well-combined in the CSPU. It is highly anticipated that this line of research will provide a facile and general method to construct various cross-linked polymer materials with superior recyclability and mechanical properties.