Cyclic phosphonate flame retardants have attracted much attention in the field of flame retardancy for their "small amount and high efficiency" characteristics. The molecular structure of this type of flame retardant contains flame retardant elements such as phosphorus and oxygen, and has a cyclic structure, which gives it unique flame retardant properties.

In terms of flame retardant mechanism, first, when thermally decomposed, the cyclic phosphonate structure can release phosphorus-containing compounds with flame retardant activity, such as phosphine and phosphine oxide, which can capture free radicals in the gas phase and inhibit the combustion reaction. Second, in the condensed phase, its decomposition products can promote the formation of a dense and stable carbon layer on the polymer surface. The cyclic structure helps to form a regular carbonized skeleton during the carbonization process, enhancing the strength and thermal insulation of the carbon layer. For example, the phosphate substances produced by the decomposition of certain cyclic phosphonate flame retardants can undergo esterification reactions with polymer molecules, cross-link to form a three-dimensional network structure, further strengthen the carbon layer, and improve the flame retardant efficiency.

In practical applications, compared with traditional flame retardants, cyclic phosphonate flame retardants only need to be added in a smaller amount to make polymer materials achieve ideal flame retardant effects. In materials such as polycarbonate (PC) and polyurethane (PU), adding an appropriate amount of cyclic phosphonate flame retardant can not only significantly improve the flame retardant properties of the materials, but also have little effect on the mechanical properties and processing properties of the materials, and can better maintain the original characteristics of the materials, achieving a good balance between flame retardant properties and comprehensive material properties, so that "small amounts" can be used to achieve "high efficiency" flame retardant goals.