A novel hyperbranched poly(phosphorodiamidate) with high expansion degree and carbonization efficiency used for improving flame retardancy of APP/PP composites

A novel P-N containing hyperbranched poly(phosphorodiamidate) (HBPPDA) was synthesized by the A 2 +B 3 polymerization, which had high thermal stability, with greater than 40 wt% of the char residue left at 750 °C. The benzene and triazine rings in HBPPDA contributed to a good char-forming capacity. Furthermore, a large number of terminal primary amines could release incombustible gases to dilute the concentration of oxygen. Thus, HBPPDA could act as blowing agent and carbonization agent simultaneously. Only 6.25 wt% of HBPPDA could greatly enhance the flame-retarding efficiency of ammonium polyphosphate (APP), showing a remarkable synergy to improve flame retardancy and dripping resistance of polypropylene (PP). When 25 wt% of flame retardant (APP:HBPPDA = 3:1) were added into PP matrix, the composite achieved V0 rating for UL-94 test, and its limiting oxygen index (LOI) value was increased to 30.6%. The reduction of 76.2% and 41.5% were available for the peak heat release rate (PHRR) and the total heat release (THR). Meanwhile, the composite showed strong smoke suppression.