Intrinsically flame-retardant polyamide 66 with high flame retardancy and mechanical properties

The key factor in the synthesis of intrinsic flame retardant polymers is the thermal stability and reactivity of phosphorus-based flame retardants. However, it is difficult to realize both thermal stability and high reactivity by using one phosphorus-based flame retardant. Herein, we proposed a strategy to improve the thermal stability of highly reactive flame-retardant, 4-(2-(((2-carboxyethyl)(phenyl)phosphoryl)oxy)ethoxy)-4-oxohexanoic acid (CPPOA), by reacting it with 1,6-diaminohexane to obtain CPPOA salt, which then was copolymerized with PA66 salt to obtain intrinsic flame-retardant polyamide 66 (FRPA66). The thermal stability of CPPOA was significantly improved. The LOI and vertical combustion grade of FRPA66 with 6 wt% CPPOA reached 27.2% and V-0 rating, respectively. Furthermore, the tensile strength and impact strength of the FRPA66 reached 70 MPa and 5.6 kJ m^-2, respectively. Our work presents an efficient approach to synthesize polymers having high flame retardancy and good mechanical properties, showing high potential for real applications.