Preparation and thermal properties of a novel DOPO‐based Schiff base derivative as a flame retardant for polystyrene

Abstract

We synthesized an acrylic acid 4-[(10-oxo-10H-9-oxa-10λ5-phospaphenanthren-10-yl)-phenylamino-methyl]-phenyl ester (DOPO-AC), a novel Schiff base derivative based on 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and evaluated its utility as a flame retardant for polystyrene (PS). The synthesized DOPO-AC was characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. The reactive vinyl groups of DOPO-AC further copolymerized with styrene to produce PS/DOPO-AC. Thermogravimetric analysis showed that DOPO-AC could clearly improve the char residue formation. By comparing the data of T 5% and T 10% , it was found that the thermal stability of the PS/DOPO-AC copolymer was reduced. We investigated the influence of DOPO-AC on the flame retardancy of PS by determining limiting oxygen indexes, conducting vertical burning tests (UL-94), and carrying out thermogravimetry combined with differential thermal analysis. These results revealed that PS containing 5 wt% DOPO-AC had a UL-94V-0 rating and a limiting oxygen index of 29.6%. Residues of PS/DOPO-AC copolymer after the UL-94V tests were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy, and FTIR spectroscopy; and the results allowed us to propose a flame retardant mechanism for PS/DOPO-AC copolymer. Taken together, our results prove that DOPO-AC is an effective flame retardant for PS.