Phosphorus-Based Flame Retardants for Polyurethanes: Synthesis and Mechanistic Studies

Polyurethanes (PUs) are a group of versatile synthetic polymer materials that have been extensively applied in the field of rubbers, flexible or rigid foams, elastomers, adhesives, and coatings. However, like most synthetic polymer materials, PUs suffer from high flammability, which potentially threatens the safety of people and property. To eliminate this potential threat, flame-retardant (FR) modification is required for PUs. Among a wide variety of FRs, phosphorus-containing compounds have attracted considerable interest because of their relatively high FR efficiency and environmental friendliness. Over the past few decades, diverse phosphorus-containing compounds have been added into PUs, either as additives or reactive FRs that can effectively improve the FR property of PUs. However, the incorporation of phosphorus-containing compounds will cause some adverse effect on the physical and mechanical properties and thermal stability. Therefore, phosphorus-containing compounds have been combined with synergistic FR agents to improve the FR efficiency and obtain exceptional comprehensive properties of PUs. The FR mechanism of phosphorus-containing compounds is discussed for both the vapor and condensed phases.