Spider Silk-Mimetic Cross-Linked Elastomer: Phenyl Phosphonate-Driven Hierarchical Hard Domain for Unprecedented Integrated Flame Retardancy, Mechanical Robustness and Recyclability

Abstract

The development of next-generation advanced elastomers is featured by superior flame retardancy, mechanical robustness, and recyclability. However, conflicting intrinsic mechanisms hinder simultaneous achievement of these traits. Inspired by spider silk’s hierarchical structures, we designed a cross-linked polyurethane elastomer (CPU) that unprecedentedly balances these attributes while excelling in each. This is accomplished by dynamically cross-linking linear polyurethane chain with a polymeric flame retardant (poly-BP) to create a hierarchical microphase-separated structure, which is driven by synergistic effects of extensive hydrogen bonds and strong binding energy between the phenyl-phosphate units (phenyl-PO(O-)2), wherein self-aggregated phenyl-PO(O-)2 units functions as major hard domains. The ingenious design endows CPU with exceptional mechanical properties, featuring a tensile strength of 42-55 MPa, elongation at break of 424-2080 %, and toughness of 240 MJ/m3. It demonstrates impressive elastic recovery, instantly returning to its original size after being stretched over ninefold in length. The CPU, with a UL-94 V-0 rating, outperforms pure elastomer by reducing peak heat release by 67 % and total heat release by 49 %. Besides, CPU exhibits self-healing capabilities and recyclability through hot-pressing or solvent, offering a safe and substantial application potential for hot melt adhesive, flexible thermal interface materials and carbon fibre composites.