Study of the flame retardancy and thermal properties of unsaturated polyester resin via incorporation of a reactive cyclic phosphorus-containing monomer

A reactive cyclic phosphorus-containing monomer (ethyl acrylate cyclic glycol phosphate; EACGP) was synthesized in a facile way and various amounts of EACGP were combined with unsaturated polyester by radical bulk polymerization. The resulting flame-retardant unsaturated polyester resin (UPR) samples were investigated using thermogravimetric analysis, limiting oxygen index (LOI), and microscale combustion calorimetry tests. Due to the high phosphorus content of EACGP, incorporation of this monomer led to a marked decrease in the peak heat release rate and the total heat release, an increase in the LOI and the combustion char formation. Furthermore, real-time Fourier transform infrared spectroscopy was employed to investigate the thermooxidative degradation behavior of UPRs and the charring effect of EACGP as well as the UPR char morphology was studied, illustrating the flame retardancy mechanism in UPR.