Effects of a symmetrical inorganic-organic monomer on the flame retardancy and mechanical properties of polyethylene terephthalate copolymers.

[Display omitted] • The synthesis of symmetrical functional monomer flame retardant with benzene ring was reported. • It is found that the amount of flame retardants introduced is not proportional to the flame retardancy. • The influence of flame retardants in a certain range on mechanical properties unchanged. • Synthesis of intrinsic flame retardant PET. In this paper, a kind of symmetric functionalized monomer is presented, and a polyester with flame retardancy and mechanical properties is obtained. Magnesium hydroxide was modified with phenylphosphonic acid to give a novel inorganic–organic monomer (MH-PPOA) with intrinsic flame retardancy. MH-PPOA was incorporated into the main chain of polyethylene terephthalate (PET) in varying amounts (n, wt% relative to terephthalic acid) to give a series of co-polyesters (MH-PPOA n -co-PET), and the effects of the monomer on their flame retardancy and mechanical properties were determined. The structure and morphology of the hybrid monomer was confirmed by Fourier transform infrared spectroscopy, and scanning electron microscopy, and its successful introduction into the polyester chain of PET was verified by proton nuclear magnetic resonance spectroscopy. The thermal characteristics, flame retardancy and burning behavior of the synthesized copolymers were evaluated by differential scanning calorimetry, thermogravimetric analysis, measurement of the limiting oxygen index (LOI), Underwriters Laboratory vertical burning (UL-94) test, and cone calorimetry. The mechanical properties were measured by tensile testing. This study provides a new direction for the introduction of intrinsic flame retardants and demonstrates that the incorporation of a symmetrical phenylphosphonic acid modified magnesium hydroxide monomer can also improve the mechanical properties of the PET copolymer. [ABSTRACT FROM AUTHOR]