Development of a DOPO-containing melamine epoxy hardeners and its thermal and flame-retardant properties of cured products



In this study, a novel Schiff base of melamine used as flame-retardant curing agent for epoxy resins, was synthesized via condensation reaction of 4-hydroxybenzaldehyde with melamine, followed by the addition of 9,10-dihydro-9-oxa-10-phosphaphen-anthrene 10-oxide (DOPO) to the resulting imine linkage. The structure of DOPO-containing melamine Schiff base (P-MSB) was characterized by Fourier transformed infrared spectroscopy, 1H-nuclear magnetic resonance (1H-NMR) and 31P-NMR. The compound (P-MSB) was used as a reactive flame retardant in o-cresol formaldehyde novolac epoxy resin (CNE) to prepare flame-retardant epoxy resins for electronic application. The thermal and flame-retardant properties of the epoxy resins cured by various equivalent ratios phenol formaldehyde novolac (PN) and P-MSB were investigated by the nonisothermal differential scanning calorimetry, the thermogravimetric analysis, and limiting oxygen index test. The obtained results showed that the cured epoxy resins possessed high Tg (165°C) and good thermal stability (T5%, 321°C). Moreover, the P-MSB/CNE systems exhibited higher limiting oxygen index (35) and more char was maintained in P-MSB/CNE systems than that in PN/CNE system and the effective synergism of phosphorus–nitrogen indicated their excellent flame retardancy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013