Liquid oxygen compatibility and thermal stability of bisphenol A and bisphenol F epoxy resins modified by DOPO

Bisphenol A and bisphenol F epoxy resins (BA and BF) were chemically modified by 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to improve their liquid oxygen compatibility. The structures of the modified epoxy resins were confirmed by Fourier transform infrared spectroscopy. Significant enhancement of liquid oxygen compatibility for the modified resins was detected according to the liquid oxygen mechanical impact test. Thermogravimetric analysis showed that during the degradation in oxygen atmosphere, the modified resins exhibited much lower weight loss rate and possessed much higher char residues than the control ones. Based on limited oxygen index test, better flame retardancy was also observed for the modified resins. In addition, the modified BA system was more excellent than the modified BF system in liquid oxygen compatibility, thermal stability, and flame retardancy. X-ray photoelectron spectroscopy analysis showed that after the liquid oxygen impact, the modified resins was still in oxidation stage and the control ones already begun to decompose and char. It could be attributed to formation of the phosphoric oxyacid on the surface of the modified resins, which prevented decomposition and inhibited the reaction between the specimen and liquid oxygen. Copyright (c) 2014 John Wiley & Sons, Ltd.