Enhanced cryogenic mechanical properties and liquid oxygen compatibility of DOPO-containing epoxy resin reinforced by epoxy-grafted polysiloxane

Excellent cryogenic mechanical properties are urgently requested for the materials used in liquid oxygen environment. However, a DOPO-modified epoxy resin (EP-P), which was compatible with liquid oxygen, had no improved cryogenic mechanical properties compared with the pure epoxy resin (EP). Besides, its mechanical properties at room temperature (RT) were obviously decreased compared with EP. Thus, a novel epoxy-grafted polysiloxane (EGP) was synthesized by dimethyldimethoxysilane, dimethoxydiphenylsilane and 3-glycidoxy-propyltrimethoxysilane through co-hydrolytic condensation reaction. EGP was introduced into EP-P to improve cryogenic mechanical properties, especially toughness of EP-P. Tensile properties and fracture toughness of the DOPO/EGP-modified epoxy resin (EP-P/Si) at RT and liquid oxygen temperature (90 K) were investigated. Compared with EP, at RT, failure strain and K_IC of EP-P/Si were increased by about 100% and 40%; at 90 K, the above two properties were increased by about 60% and 50%. Besides, EP-P/Si had almost same tensile strength with EP at both RT and 90 K. The results of the liquid oxygen mechanical impact test indicated that EP-P/Si was still compatible with liquid oxygen. XPS analysis showed that EP-P/Si had lower oxidation degree after the impact test compared with EP-P, indicating that liquid oxygen compatibility was enhanced.