o-Phenylenediamine-derived phosphorus-based cyclic flame retardant for epoxy and polyurethane systems

The present study attempts the synthesis of a cyclic multifunctional flame-retardant (FR) moiety from o-phenylenediamine (OPDA) as the starting material. OPDA was reacted with phenylphosphonic dichloride and further with the 3-monochloro-1,2-propanediol to obtain the final product (FRPOL) which was then incorporated into epoxy and polyurethane coating systems. The structure of the synthesized molecule was confirmed using hydroxyl value, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The cured coating films were characterized for thermal, mechanical and flame-retardant properties. Thermogravimetric analysis and differential scanning calorimetry were used to carry out the thermal degradation studies and to know the glass transition temperatures ( T g ), respectively. The thermal and mechanical properties were excellent after the incorporation of the synthesized molecule into the coating systems. The limiting oxygen index (LOI) and UL-94 vertical burning tests were carried out to check the flame retardancy of the cured coating films. The polyurethane with FR had the maximum LOI value of 32 while the epoxy with 45% concentration of FR had a maximum LOI value of 26 among all the coating formulations. The formulations with FRPOL displayed self-extinguishing behavior with no dripping in UL-94 test. Graphic abstract