Reactive flame retardant, also known as structural flame retardant, is a type of flame retardant that participates in the reaction during polymerization or polycondensation and is bonded to the main chain or branch of the polymer. The flame retardant is easy to migrate, cannot maintain the flame retardant effect for a long time and destroy the physical properties of the foam. It has good stability, not easy to disappear, small addition, low toxicity, and has little effect on polymer performance.

　　Flame retardant elements or groups can be introduced through isocyanate or polyol. Due to technical and cost reasons, the method of introducing flame retardant elements into isocyanate is rarely used at present. Such flame retardant polyols mainly include halogen-free phosphorus-containing polyol Exolit OP550, phosphorus-containing reactive flame retardant An-tiblaze PR82, halogenated polyether polyol Ixol M125, organic phosphorus halogen compound reactive flame retardant FRT-4 , Tetrabromophthalate diol, tris (dipropylene glycol) phosphite, N, N-bis (2-hydroxyethyl) aminomethylphosphonic acid diethyl ester, etc. Huang et al. Prepared the montmorillonite nanocomposite (c-MMT) by ion exchange method, successfully inserted the nitrogen-phosphorus structure containing quaternary ammonium salt into the interlayer of nano-montmorillonite, and added it to the polyurethane foam In the results of the cone calorimeter measurement, the peak heat release rate (PHRR) of the PU system with c-MMT (mass fraction 20%) was reduced by 25% compared to the standard PU. Scanning electron microscopy shows that c-MMT contributes to the formation of carbonaceous material during PU combustion and makes its distribution more uniform, hindering the transfer of heat and air to the internal substrate, thus effectively playing a flame retardant role. The BASF patent introduces a foaming system composed of halogenated polyols, brominated polyols, flame retardants, catalysts, surfactants, foaming agents and other components. The flame spread index and smoke of PUF products prepared The density exceeds the American flame retardant standards ASTME-84 and FM 4880.

　　Rotaruetal. Used Mannich reaction to synthesize a new polyether polyol with high nitrogen content and good thermal stability by using raw materials such as diethanolamine, paraformaldehyde, cyanuric acid, propylene oxide, etc., and prepared this Mannich polyol PUF foam. The results show that, due to the presence of isocyanuric rings in the PU foam system, the PUF foamed by this Mannich polyol has better mechanical strength, and has better thermal stability than traditional aliphatic PU foam systems. And higher flame retardant efficiency. Paciorek Sadowska J et al. Synthesized a reactive boron-containing flame retardant polyol using N, N′-bis (methylene epoxy-2-hydroxyethyl) urea and boric acid derivatives. Compared with standard PUF, The PUF prepared by this boron-containing flame retardant polyol, when the added mass fraction of boron-containing polyol is increased from 1% to 4%, the compressive strength of PUF is increased from 241.9 kPa to 398.7 kPa. According to the flame test, the PUF added with boron-containing polyol can reach the self-extinguishing level, and the retention amount can be up to 91.2%, while the standard PUF retention amount is only 67.3%. The results show that the boron-containing flame retardant polyol is not only the polyol raw material reacted with isocyanate, but also boron and chlorine in the PUF structure can play a flame retardant role. Yanchuk [32] et al. Prepared a series of vinyl diphosphate salts and applied them to PUF to improve the flame retardant properties of PUF. Experiments have shown that with the increase of vinyl diphosphate salt content, the flammability of PUF is significantly reduced, and the flame is extinguished from the flame. Biomass resources are abundant and renewable in nature. In addition to the promulgation of various environmental protection laws and the improvement of people's energy-saving awareness, biomass-type PUF has attracted people's attention. Melissa Heinen et al. Used epoxy soybean oil extracted from plants to react with phosphoric acid to produce phosphorylated polyols, and then used different proportions of phosphorylated polyols to react with glycerin and ethylene glycol polyester, using pentane as a blowing agent The phosphorylated PUF is obtained. SEM, SDT-FTIR and flammability test results show that the flame retardancy of the phosphorylated PUF is as good as that of commercial products, and the LOI of phosphorylated PUF can be even higher.