Photopolymerization and thermal behaviors of acrylated benzenephosphonates/epoxy acrylate as flame retardant resins

Di(acryloyloxyethyl) benzenephosphonate (DABP) and acryloyloxyethyl phenyl benzenephosphonate (APBP) were synthesized starting from phenylphosphonic dichloride, and characterized by FT-IR and 1H NMR. DABP and APBP were blended in the ratios of 10–50 wt.% with a commercial epoxy acrylate oligomer (EB600) to obtain a series of flame retardant UV-curable formulations. The viscosity of the formulations greatly reduced by the addition of the reactive monomers, whereas the photopolymerization rate according to the photo-DSC analysis increased. The thermal degradation behavior and flame retardancy of the UV-cured films were investigated by thermogravimetric analysis and the limiting oxygen index (LOI). The results revealed that the blended epoxy acrylates with DABP or APBP possess improved thermal stability at elevated temperature and have higher char yields, together with higher LOI values. The data from dynamic mechanical thermal analysis showed that DABP and APBP have good miscibility with EB600. The crosslink density increased along with the content of DABP or APBP in the blend, whereas the glass-transition temperatures of the blended resins decreased compared to pure cured EB600.