Synthesis, Structures, and Properties of a New Pentaerythritol-Derived Flame Retardant Used in Polyamide 66

[Image: see text] A melting phosphorous-based flame retardant (FR) named as diphenyl phosphoryl (DPP)–PEPA is synthesized from 2,6,7-trioxa-1-phosphabicyclo-(2.2.2)-octane-4-methanol (PEPA) and diphenyl phosphoryl chloride. The melting DPP–PEPA FR possesses high thermostability with T(5wt%) at 344 °C, which can match the melt-spinning of engineering plastics at high temperatures. The structure of DPP–PEPA is defined by nuclear magnetic resonance and infrared spectrometry. The influences of DPP–PEPA on polyamide 6,6 (PA66) are assessed in terms of rheology parameters and crystallinity. It is observed that the flame retardancy of PA66 is greatly improved when DPP–PEPA is added to the PA66 resin. The results show that the modified PA66 has limited oxygen index as high as 29.4%, and the compact char layers are obviously formed on top of the burned samples. As compared to the pure PA66, the peak heat release rate and the average effective heat of combustion are decreased by 26.5 and 19.3%, respectively. It is obtained that the value of flame retardancy index is 1.4, indicating high efficiency of the entire flame retardancy. Moreover, pyrolysis of DPP–PEPA is carried out at different temperatures for identifying gaseous products and types of flame retardancy.