A facile method to flame-retard epoxy resin with maintained mechanical properties through a novel P/N/S-containing flame retardant of tautomerization

A novel phenylphosphonic di-benzothiazolyl amide (PPDAB) and its imine-type tautomer were successfully synthesized via the amidation of phenylphosphonic dichloride (PPDC) with 2-aminobenzothiazole (ABZ), and used to flame-retard epoxy resin (EP). In the help of PPDAB-Amine as an additive-type flame retardant and PPDAB-Imine as a reactive-type flame retardant, PPDAB showed excellent general properties in epoxy resin. EP with 0.69 wt% of phosphorus achieved UL-94 V-0 rating, and the LOI value of it was increased to 31.0%. Compared with the EP, its performances in terms of the peak of heat release rate (PHRR), total heat release (THR), and smoke production rate (SPR) obtained from cone calorimeter were obviously improved. Besides, EP-PPDAB in which the amount of PPDAB was lower than 10 wt% also exhibited similar glass transition temperature (Tg) to EP, and well-maintained mechanical properties in terms of tensile strength and impact strength.