Phosphorus FR radical FR mechanism

PO^. radical formation is analysed for phosphorus PIN flame retardants on cotton, to understand gas phase fire protection. Formation of PO^. radicals from Triethyl phosphate (TEP), Tris-phosphoramidate (TD) and Diethyl phosphoramidate (DEPAm), both neat and on cotton, were studied in controlled pyrolysis chambers Neat DP, DEPAm and TEP do not generate PO^. radicals. Neat TD releases mainly diethylmethylphosphte (DEMP) and TEP from 250 – 300 °C upwards and then ethene at higher temperatures, as well as diethylamine and other nitrogen compounds from around 350°C. TD-coated cotton however shows more complex decomposition products, including four main P species (phosphorus oxide, phosphenous acid HOPO, DEPAm, TEP) from 300 – 360°C with phosphorus radical PO^. formation from 400°C. The authors conclude that PO^. radical formation (which contributes to gas-phase flame retardant action: fire quenching) results from the PIN FR – substrate reaction not from the PIN FR alone, so can be modified by e.g. FR-substrate cross-linking.

“On the hunt for the PO radical: How substrate interactions shape the gas-phase mechanism of phosphoramidate flame retardants”, N. Tomasik, R. Otto, T. Mayer-Gall, B. Atakan et al., Polymer Degradation and Stability 248, 112025 https://doi.org/10.1016/j.polymdegradstab.2026.112025