A novel nitrogen–phosphorus
flame retardant (P–N
FR) based on phosphonamidate, dimethyl N,N′-1,3-phenylenebis(P-methylphosphonamidate) (DMPMP),
was successfully synthesized and its flame-retarding performances
and thermal degradation were compared with those of other P–N
FRs and a phosphorus-based FR such as resorcinol bis(diphenyl phosphate)
(RDP). DMPMP was applied to acrylonitrile–butadiene–styrene
(ABS) and ethylene–vinyl acetate (EVA) to investigate the factors
governing the flame-retarding behaviors of P–N FRs which would
make them efficient for noncharrable polymers. V-0 ratings were achieved
at 20 wt % loading of DMPMP for ABS and at a much lesser amount of
DMPMP loading (10 wt %) for EVA. Meanwhile, no rating and V-2 were
achieved even at 20–30 wt % loading of other P–N FRs
or RDP for ABS and EVA, respectively. The results from thermogravimetric
analysis, Fourier transform infrared, and UL-94V indicated that DMPMP
is a highly efficient FR and acts mainly in a gas-phase flame-retarding
mode of action. The condensed phase of DMPMP also contributed to the
flame retardancy property through −NH– groups which
tendentiously generate a nitrogen–phosphorus-rich residue because
of the intermolecular coupling transesterification reaction. These
results demonstrated the assumption that DMPMP has a high P content
and good hydrostability, which exhibits good flame retardancy for
noncharrable polymers such as ABS and EVA.