Summary A halogen‐free flame retardant with a macromolecular structure is presented. Its synthesis proceeds via polymerization of phosphorus‐containing acrylate monomers. The flame retardant was incorporated into poly(ethylene terephthalate) by extrusion. Samples with different concentrations (0.5, 2.5, and 5.0 wt%) as well as a 25 wt% masterbatch were prepared. All samples were transparent and colorless without any visible irregularities. Thermal investigations reveal an unchanged glass transition temperature. Tensile tests show the typical mechanical behavior of poly(ethylene terephthalate), but with an elevated Young's modulus. The burning behavior was investigated by several small‐flame tests in vertical and horizontal orientation, as well as by cone calorimetry. It is shown that samples with 2.5 wt% flame retardant pass the vertical UL94 test (V‐2, 20‐mm flame). The sample cannot be ignited in the horizontal fire test according to FMVSS 302. The oxygen index was measured to 28 vol%. Cone calorimetric measurements show that the effective heat of combustion as well as the total heat evolved is reduced.

A macromolecular halogen-free flame retardant, poly(N-[3-oxopropylmethylphosphinate]ethyleneimine) (PN) has been developed. This material contains both phosphorus and nitrogen. A simple and scalable process for chemical synthesis on commercial scale is described. FTIR, 1 H and 31 P NMR spectroscopy were utilized for characterization. The compound has a glass transition temperature of 82 C and is thermally stable up to 330 C. Samples of polyamide 6 containing 1 to 10 wt% of PN were prepared in a kneader. The flammability of polyamide 6/PN blends was investigated using the UL 94 vertical fire test, limiting oxygen index measurements, cone calorimetry, and the glow wire test. Samples containing loadings of 1 wt% and 10 wt% PN have V-2 and V-0 ratings, respectively. Specimen containing polyamide 12/PN blends were prepared by extrusion and injection molding for mechanical characterization.