Flame-Retardant and Mechanical Strong Polyurethane Foam Enabled by Hydrogen-Bonded Phosphonate Networks

The inherent contradiction between flame-retardant improvement and mechanical deterioration in polymers modified by conventional phosphates remains unresolved, primarily due to plasticization-induced chain slippage and interfacial incompatibility. Herein, a bulky polycyclic phosphonate (TDPP) featuring a high phosphorus content (26%) and abundant P═O groups was successfully synthesized and introduced to overcome this conflict in flexible polyurethane foam (FPUF). The unique architecture of TDPP enables multiple hydrogen-bonded cross-linking with the urethane groups of polyurethane, forming a reversible energy-dissipating network that offsets plasticization. Remarkably, TDPP enhances the compressive strength of FPUF by 50.1%, tensile strength by 20.3%, and resilience by 15.5% compared to neat FPUF, while maintaining cell structural integrity. Additionally, TDPP significantly increases the limiting oxygen index (LOI) to 27% and reduces the peak heat release rate by 30.8% via both condensed-phase barrier and gas-phase radical quenching. Crucially, TDPP-filled FPUF retains 98% of its LOI (26.5%) after thermal aging (125 °C, 16 h), whereas commercial dimethyl methylphosphonate (DMMP)-modified FPUF suffers complete flame retardancy loss. This work presents a breakthrough in reconciling mechanical and fire-safety performance in FPUF through molecularly engineered hydrogen-bonding interactions and phosphorus-rich chemistry.