Preparation and performance of nitrogen–phosphorus–silicone-containing flame retardant UV–curable coatings with high transparency

UV-curable transparent silicone-modified flame retardant materials are highly desired because they usually serve as protecting polymer matrix from moisture, ionic contaminants and particulates in vast fields such as coatings, electronic devices attributed to their merits such as high flame-retardant efficiency, high curing efficiency and low volatile organic chemical emissions. In this paper, nitrogen–phosphorus–silicone-containing flame retardant UV-curable coatings were prepared from nitrogen–phosphorus–silicone-containing acrylate and thiol-containing silicone hyperbranched polymers by UV initiated thiol-ene click reaction. It shows that these coatings were with fairly high transmittance, pencil hardness and initial decomposition temperature (Td5) of 80.7–96.9 % (400–800 nm), 9H, and 159–185 °C, respectively. Vertical burning behavior of the UV-curable coatings prepared with different acrylate derivatives was investigated and the self-extinguish time for the coatings prepared from POPHA was about 9 s. To make clear of the flame retardant mechanism, cone calorimetric test and XPS spectra of UV-curable coatings, and SEM images for the surface morphology of the chars were carried out. SEM images of the chars show that there is fine and dense white SiO2 “in-situ” generated during the course of combustion spreading on the surface. It also shows that honeycombed-like structures attributed by nitrogen and phosphorus form a quite good barrier to heat, oxygen and other flammable gas. Therefore, a ternary synergistic flame retardant mechanism of phosphorus, nitrogen and silicone elements in the UV-curable coatings was proposed. This work denotes that it is a good method to develop nitrogen–phosphorus–silicone-containing flame retardant transparent UV-curable materials.