## 3 Results and Discussion
### Liquid Oxygen Compatibility of EP/BCI/BSEA Composites
#### 3.1.2 XPS Analysis before and after 98J LOT  
XPS was conducted to research the elemental composition of EP composites before and after 98J LOT and explore the mechanism of BSEA affecting the LOC of EP. The C1s spectra of pure EP, EP/BCI/BSEA-2 and EP/BCI/BSEA-5 before and after 98J LOT are exhibited in Figure 4, and the corresponding peak fitting values are summarized in Table 3. As exhibited in Figure 4(a-c,a1-c1), the C1s peak-differentiating and imitating results before and after 98J LOT at around 283.98 eV, 285.43 eV, 287.99 eV and 289.99 eV were ascribed to C-C/C=C/C-H bonds, C-O-C/C-OH/C-N bonds, a C=O bond and COOR [39; 40], respectively. As summarized in Table 3, the C-C/C=C/C-H content of pure EP was decreased after impact, but the C-O-C/C-OH/C-N content and C=O bond content were improved and the COOR appeared. This is probably because C-C/C-H bonds can decompose into carbon radicals and \(\cdot\)H under high-energy mechanical impact, which is more conductive to the combination of oxygen radicals to form C-O-C, C=O and COOR bonds under a liquid oxygen environment. Moreover, the C-O-C/C-OH/C-N content of EP/BCI/BSEA-2 and EP/BCI/BSEA-5 was decreased after impact, but the C-C/C=C/C-H content and C=O content increased. This mainly because the C-OH bond of BSEA-modified EP broke into carbon radicals and \(\cdot\)OH and regenerated C=C and C=O bonds under the oxygen-rich environment. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{3}{c}{**Experimental Phenomena (Number of Times)**} & \multicolumn{1}{c}{**Total Number**} & \multirow{2}{*}{**IRS (\%)**} \\ \cline{2-2} \cline{4-6}  & **Burning** & **Explosion** & **Flash** & **Charing** & & **of Tests** \\ \hline Pure EP & 0 & 1 & 2 & 0 & 20 & 10.5 \\ \hline EP/BCI-25 & 0 & 1 & 2 & 0 & 20 & 10.5 \\ \hline EP/BCI/BSEA-2 & 1 & 0 & 0 & 1 & 20 & 7.0 \\ \hline EP/BCI/BSEA-3 & 0 & 0 & 0 & 2 & 20 & 4.0 \\ \hline EP/BCI/BSEA-4 & 0 & 0 & 0 & 0 & 20 & 0 \\ \hline EP/BCI/BSEA-5 & 0 & 0 & 0 & 0 & 20 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Impact sensitivity phenomena of modified EP. Figure 3: Schematic of (**a**) pure EP, (**b**) EP/BCI-25, (**c**) EP/BCI/BSEA-2, (**d**) EP/BCI/BSEA-3, (**e**) EP/BCI/BSEA-4, (**f**) EP/BCI/BSEA-5 after impact in liquid oxygen. The O1s spectra of EP/BCI/BSEA-2 and EP/BCI/BSEA-5 before and after impact are shown in Figure 5, and that of pure EP is shown in Figure S1. The relevant peak fitting values of O1s are shown in Table 4. As exhibited in Figure 5(a,b,a1,b1), the O1s peak-differentiating and imitating results of EP samples before and after liquid oxygen impact at around 531.45 eV and 532.10 eV were attributed to the C=O band and C-O-C [41]. The peak fitting data in Table 4 show that the relative amount of C=O bonds improved, while the amount of C-O-C bonds was reduced. This is mainly attributed to the fact that the R-OH in the molecular structure was attacked under 98] LOT in the cryogenic environment to generate C=O. The specific reaction route is exhibited in Figure 6 on the right. Firstly, the R-OH in the EP matrix was attacked to generate R- and -OH radicals. Secondly, the R-radicals may react with liquid oxygen to generate ROO radicals, and the ROO radicals  
Figure 4: C1s spectra of pure EP (**a**) before and (**a1**) after, EP/BCI/BSEA-2 (**b**) before and (**b1**) after, EP/BCI/BSEA-5 (**c**) before and (**c1**) after the liquid oxygen compatibility test.