Abstract: A reactive phosphorus-containing flame-retardant monomer was synthesized by a one-step method and introduced into the molecular chain of poly (m-phenylene isophthalamide) by low-temperature solution polymerization to obtain the phosphorus-containing poly (m-phenylene isophthalamide), and its mechanical properties, thermal properties, and flame-retardant properties were investigated. The results show that when the addition of phosphorus-containing flame-retardant monomers in diamine reaches 5% (mole fraction), the tensile strength of the phosphorus-containing poly (m-phenylene isophthalamide) remains at 94.9 MPa; the modulus reaches 1 619.8 MPa, and the glass transition temperature reaches 270.4 ℃; the residual carbon rate increases to 69.3% in thermogravimetric tests, and the limiting oxygen index reaches 42.8%. Compared with the poly (m-phenylene isophthalamide), the heat release capacity decreases by 41.1%; the peak heat release rate decreases by 67.9%, and the total heat release decreases by 67.6%. Therefore, the method synthesizes a highly efficient reactive phosphorus-containing flame-retardant monomer and prepares the phosphorus-containing poly (m-phenylene isophthalamide) with excellent flame retardancy and high strength.

Key words: reactive phosphorus-containing flame-retardant monomer, poly (m-phenylene isophthalamide), phosphorus flame retardant, phenylphosphonic dichloride