N-P PIN FRs for epoxy
Three N-phosphorylated iminophosphoranes, with different P oxidation states, were tested, in one case achieving UL 94 V-0. The three N-P PIN FRs were derived, by reaction with sodium azide (NaN3) and trimethyl phosphite, of:
- DPP (diphenyl phosphite) +3;
- DOPO* - oxidation state +1;
- DPPO (diphenylphosphine oxide), oxidation state -1.
The resulting N-phosphorylated iminophosphoranes were then added to epoxy (TGDDM-MTHPA) at the reaction stage at 2.5 – 10% loadings. All three PIN FRs improved the high-temperature thermal stability of the epoxy, and improved fire performance. The best fire performance was achieved 10% DPP-based FR (highest oxidation state): LOI increased by 35% (compared to neat epoxy), peak heat release rate reduced by 64%, UL 94 time to extinguishment reduced from 2 minutes to 7 seconds and UL 94 V-0 achieved (thickness not specified). The authors consider that the better fire performance of the DPP-derived PIN FR is due to better char production. This conclusion that higher oxidation state corresponds to more char is conform to other publications, see pinfa Newsletter n°170.
* 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide
“Synthesis of novel N-phosphorylated iminophosphoranes and their application in flame-retardant epoxy resin”, C. Ji et al., J. Taiwan Institute of Chemical Engineers 171 (2025) 106064 https://doi.org/10.1016/j.jtice.2025.106064
