A DOPO-base Schiff derivative used as a flame retardant for polystyrene

A novel 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based Schiff base derivative, 6,6′-(1,4-phenylenebis (((3-hydroxyphenyl)amino) methylene)) bis (dibenzo [c,e] [1,2] oxaphosphinine 6-oxide) (SD), was synthesized and applied to polystyrene. The structure of terephthalaldehyde dihydroxymethane benzene and SD are characterized by Fourier-transform infrared (FTIR) spectroscopy, 1 H-nuclear magnetic resonance spectroscopy, and elemental analysis. The results of thermogravimetric analysis tests show that the residue of the SD/PS composites increased from 0.21 to 7.09% with the increase of SD content, indicated that the thermal stability of the SD/PS composites was significantly improved. The introduction of SD also efficiently ameliorated the flame-retardant property of SD/PS composites with limiting oxygen index increased by 33.15%, rated UL-94 vertical burning test V-0 rating, lower peak heat release rate, and total heat release. The mechanism of SD/PS composite was explored by scanning electron microscopy images and FTIR spectra of residue of SD/PS composites after calcination by muffle furnace. These tests prove that SD can be used as an effective polystyrene (PS) flame retardant.