Study of the epoxy/amine equivalent ratio on thermal properties, cryogenic mechanical properties, and liquid oxygen compatibility of the bisphenol A epoxy resin containing phosphorus

A liquid oxygen-compatible epoxy resin is successfully prepared by changing the epoxy/amine equivalent ratio (SR) of a phosphorus-containing epoxy resin. The liquid oxygen impact test results showed that the modified resin was compatible with liquid oxygen only when the SR was 0.8. The mechanical properties at 90 K showed that the strain energy and impact toughness reached the maximum when the SR was 0.8, which suggested that the reduced rigidity might be beneficial to improve the liquid oxygen compatibility of the polymer. The thermomechanical and thermal results showed that the cross-linking density and thermal stability was proportional to SR. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis showed that the P=O group in the resin decomposed into phosphoric oxidative solids and P-N intermediates to inhibit the resin from decomposing and contacting with liquid oxygen during impact. Overall, this study provides a new idea for the design of liquid oxygen-compatible epoxy resin.