Phosphorus PIN-FR reacted into the polymer results in fire and mechanical performance with no FR leaching. The commercial PIN phosphorus FR (DDP*) is synthesised from DOPO** and itaconic acid. This was reacted into a polyester diol from DDP, adipic acid, ethylene glycol and 1,4-butadeniol, and then used to prepare polyurethane elastomers (FR-PUE) with 0.14 -0.72% P content. At 0.29% P, the FR-PUE showed LOI (Limiting oxygen index) of 23 (compared to 19 for neat PUE) and achieved UL94-V0 (thickness not specified), whilst offering improved tensile strength.
“Synthesis of reactive DOPO-based flame retardant and its application in polyurethane elastomers”, H. Wang et al., Polymer Degradation and Stability 183 (2021) 109440, https://doi.org/10.1016/j.polymdegradstab.2020.109440