Three novel phosphorus-containing Salen-based derivatives (Salen-DPCP-M: M = Ni, Zn, and Mn), which include both phenyl phosphate structures (DPCP) and Salenmetal complexes, were prepared for enhancing the fire safety of thermoplastic polyurethane (TPU). Thermogravimetric analysis (TGA) showed that Salen-DPCP-M altered the thermal degradation pathways of TPU probably due to the phosphoruscontaining structure of Salen-DPCP-M. The cone calorimeter test showed that the addition of 3 wt% of Salen-DPCP-Ni, Salen-DPCP-Zn, and Salen-DPCP-Mn lowered the peak of heat release rate (PHRR) from 1495 kW/m 2 for neat TPU to 690, 875, and 813 kW/m 2 , respectively, for the TPU composites, which demonstrated that Salen-DPCP-M improved the fire safety of TPU. In addition, the release of toxic CO gas from the Salen-DPCP-Ni/TPU and Salen-DPCP-Zn/TPU composites was reduced by 78.2% and 80.0%, respectively. The results of TGA/infrared spectrometry (TG-FTIR) showed that the incorporation of Salen-DPCP-Ni promoted the release CO 2 , while reducing the formation of harmful gases. Laser Raman spectroscopy (LRS) and scanning electron microscopy (SEM) showed that Salen-DPCP-Ni/TPU and Salen-DPCP-Zn/TPU composites formed a dense and stable char layer. Herein, the mechanism of these flame retardants containing novel phosphorus-containing Salen-metal complexes is also proposed. K E Y W O R D S fire safety, metal, phosphorus, Salen 1 | INTRODUCTION Salen derivatives have been widely used in a variety of applications, including catalytic, 1 antitumor therapy, 2 and antimicrobial treatment. 3 At present, their use in the field of flame retardants is attracting attention because the Schiff base structure of Salen shows good flame retardancy in polymers. Fontaine et al introduced N,N 0 -bis (4-hydroxysalicylidene) ethylenediamine copper(II) complex (CC2) and N,N 0 -bis (5-hydroxysalicylidene) ethylenediamine copper(II) complex (CC3) into a thermoplastic polyurethane (TPU) matrix. The peak heat release rate (PHRR) of flame-retarded TPU with 10 wt% CC2 or CC3was reduced significantly, by approximately 50% compared with that of neat TPU. 4 Naik et al showed that the Salen-type Schiff base derivative could undergo polycondensation by covalent cross-linking, via a mechanism similar to that of the formation of phenolic/resorcinol resins, indicating that the Salen-type Schiff base had an effective flame retardant effect, mainly in the condensed phase. 5 Other studies on Salen-based flame retardants in TPU have also been reported. 6,7 Although Salen-type Schiff base derivatives can be used to produce flame-retarding polymers,the thermal cross-linking process of the Salen component mainly occurs in the condensed phase and has no significant effect on the gas-phase during the combustion of polymers.Phosphorus-containing flame retardants are of major interest because of their high flame retardancy both in gas and condensed