Isosorbide-derived boron- and phosphorus-containing precursors for flame-retardant epoxy coating

The present study describes an attempt to induce the inherent flame retardancy to the epoxy resin by incorporation of phosphorous and boron atoms in the polymer backbone through the curing agents. Phosphorous (PPc)- and boron (BPc)-containing precursors were synthesized and incorporated into the commercial epoxy and hardener system with different molar ratios. The structures of the synthesized compounds were confirmed using hydroxyl value, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The thermal, physical, and mechanical properties of the cured films were performed using different testing methods. Thermogravimetric analysis and differential scanning calorimetry results showed the overall increased thermal stability and char yield along with the glass transition temperatures (T) due to the incorporation of newly synthesized phosphorus- and boron-containing compounds in the coating films. The mechanical properties and solvent resistance of the cured films were excellent. The flame-retardant properties of the cured films were increased with the incorporation of PPc and BPc. The highest limiting oxygen index was obtained for the formulation with equal amounts of PPc and BPc as 29 while UL-94 showed the self-extinguishing behavior within 10 s after ignition.