Synthesis and Investigation of the Flame Retardancy, Mechanism, and Comprehensive Properties of a Reactive Flame-Retardant UV-Curable Acrylate Monomer

A reactive flame-retardant acrylate monomer (PEDP) with a high phosphorus content has been synthesized through a straightforward process to improve the fire safety of UV-curable materials. In comparison to the traditional monomer PETA, the UV-cured PEDP (UV-PEDP) enhances the limiting oxygen index (LOI) from 28.7% to 31.9% and achieves a UL-94 V0 rating without any melt dripping. Meanwhile, UV-PEDP exhibits a 42.7% reduction in peak heat release rate (PHRR) and a 30.6% decrease in total heat release (THR) compared to UV-PETA in the cone calorimetry test (CCT). Mechanistic analysis attributes the improved flame retardancy to gas-phase quenching and dilution effects from phosphorus-containing decomposition products, as well as the formation of char in the condensed phase. The UV-PEDP demonstrates high transparency (exceeding 80% at 800 nm) and excellent hardness (above 93 Shore-D). Although there is a decrease of 27% in tensile strength and 30% in elongation, these trade-offs remain acceptable for many coating applications. This study presents an effective strategy to expand the safe use of UV-curable materials.