Durable macromolecular firefighting for unsaturated polyester via integrating synergistic charring and hydrogen bond

• Arylamine-DOPO-bearing polyphosphoester (PPDSP) has been designed and used as a green macromolecular flame-retardant. • Hydrogen bond between PPDSP and UP matrix significantly improves thermal properties. • PPDSP exerts synergistic charring effect and greatly increases the fire safety of UP. • Modified-UP exhibits superior flame-retardant durability and water resistance. Frequent fire accidents and increasing environmental/health issues call for more durable and safer firefighting strategy for polymeric materials. Widely used small-molecule flame retardants are limited for their damage to thermal/mechanical properties, poor durability, undesirable persistence, bio-accumulation and toxicity (PBT). Herein, a novel macromolecular flame retardant, arylamine-DOPO-bearing polyphosphoester (PPDSP) has been synthesized and added to the unsaturated polyester (UP). On the one hand, hydrogen bond between arylamine group of PPDSP and UP network enhances the interchain interaction and compatibility. On the other hand, the phosphoester and DOPO groups can generate high-oxidized phosphorus-containing acids at high temperature, which further catalyze the dehydration reaction of arylamine and UP matrix into dense char-layers and exert the synergistic charring effect. By integrating the hydrogen bond and synergistic charring effects into PPDSP macromolecule, the obtained UP/PPDSP resins exhibit excellent fire safety, flame-retardant durability, heat-resistance and impact strength. Compared with UP, the T g and T 5% of UP/PPDSP20 are increased by 11 °C and 20 °C, respectively. The LOI value reaches 27.3%, the UL-94 rating is V-0 and the peak heat release rate is reduced by 58%. Even after one year of normal storage or one week of water soaking, the original flame retardant performance is maintained. Hence, this macromolecular firefighting strategy provides an efficient, durable and green pathway for improving the fire safety of polymers.