## 3 Results and Discussion  
### Characterization of Serial Disulfide Polymer  
In the infrared spectrum of the poly(S-DAP) copolymer (Figure 5a), compared with the curve of DAP, the curve of poly(S-DAP) copolymer showed an extra signal at 462 cm\({}^{-1}\), which illustrated the existence of S-S bond. In Figure 5b, the curve of tung oil showed a signal at 3011 cm\({}^{-1}\), which was caused by the vibration of =C-H bond, and the signal at 993 cm\({}^{-1}\) was attributed by three conjugates C=C. In the curve of poly(S-T) copolymer, the signals at 1581 and 799 cm\({}^{-1}\) were caused by the vibration of C-H bond which was near the C-S bond, and there was also an indicator of S-S bond at 461 cm\({}^{-1}\). In Figure 5c, the curves of peanut oil and poly(S-P) copolymer resembled each other, but the signal at 3009 cm\({}^{-1}\) disappeared and a new signal at 468 cm\({}^{-1}\) appeared, which indicated that S had reacted with the C=C bond. In Figure 5d, compared with the curves of peanut oil and styrene, the curve of poly(S-Sty-P) terpolymer changed a lot: A new signal at 468 cm\({}^{-1}\) showed the existence of S-S bond; and the signals at 700, 776, and 3010 cm\({}^{-1}\) indicated that the styrene was participated in the reaction. The signal at 1748 cm\({}^{-1}\) was attributed by the vibration of C=O bond. However, the signal at 1630 cm\({}^{-1}\) disappeared, while the signal of the benzene ring still existed. It meant that the poly(S-Sty-P) terpolymer had been successfully synthesized. In order to be fully blended with conductive additives and to be uniformly filled on the collector, the products were separately dissolved in different solvents to find out the most suitable system. The poly(S-DAP) copolymer, poly(S-T) copolymer, poly(S-P) copolymer, and poly(S-Sty-P) copolymer were separately added into different solvents: Acetone, dichloromethane, trichloromethane, cyclohexane, toluene, and tetrahydrofuran. The mixture was separately put into ultrasonic cleaners for 25 min and stayed still for 24 h. The result showed that poly(S-Sty-P) terpolymer had the best solubility in tetrahydrofuran, as shown in Table 1. The solubility of this disulfide polymer was based on their molecular chain structure. Tung oil had three conjugated C=C bonds in the structure and DAP had two C=C bonds, which can easily form a cross-linking structure after reverse vulcanization [12,20]. Figure 5: (**a**) The infrared spectrum of poly(S-DAP) copolymer and contrast DAP; (**b**) the infrared spectrum of poly(S-T) copolymer and contrast tung oil; (**c**) the infrared spectrum of poly(S-P) copolymer and contrast peanut oil; (**d**) the infrared spectrum of poly(S-Sty-P) terpolymer and contrast peanut oil, styrene. Therefore, these two copolymers had worse solubility. Peanut oil contained many unsaturated glycerides. Though it had fewer C=C bonds, molecular crosslinking still existed [21]. Therefore, its solubility was still unsatisfactory. However, in the structure of poly(S-Sty-P) terpolymer, the benzene ring existed, so the internal crosslinking of the molecular chain was reduced by the larger steric hindrance [22]. Thus, its solubility was improved. Furthermore, nuclear magnetic resonance carbon (\({}^{13}\)C NMR) characterization was used to demonstrate the terpolymer's structure. In the \({}^{13}\)C NMR spectra of poly(S-Sty-P) terpolymer (Figure 6), the signals at the range of 125-129 ppm were attributed by the C=C bond vibration. It meant that benzene ring existed in the molecular chain of the terpolymer. However, intramolecular crosslinks might also exist during the reaction, as shown in Figure 6. There were also new signals at 51 and 21 ppm, which indicated that carbon atoms were successfully attached to sulfur. As poly(S-Sty-P) terpolymer had the best solubility compared with other disulfide polymers, it was chosen to be utilized as the cathode material in Li-S battery.