## 2 Materials and Methods
### Materials
A solution of Cl\({}_{3}\)P=NSiMe\({}_{3}\) (1.08 g, 4.80 mmol) in CH\({}_{2}\)Cl\({}_{2}\) (20 mL) cooled to \(-\)55 \({}^{\circ}\)C was added dropwise to a solution of PCI\({}_{5}\) (2 g, 9.59 mmol) in CH\({}_{2}\)Cl\({}_{2}\) (50 mL) placed in a three-necked flask. The reaction mixture was allowed to warm to room temperature and stirred with a magnetic stirrer. The conversion of monomer to monophosphazene salt was monitored by 31P NMR spectrometry. After complete conversion, all volatiles were removed under vacuum. The resulting product was obtained as a white-colored crystalline solid. Yield: 2.37 g (93%). 31P NMR (CDC\({}_{3}\)): \(\delta_{\rm P}\) = 21.5 ppm (s, -PCI\({}_{3}\)\({}^{+}\)), \(\delta_{\rm P}\) = \(-\)292.5 ppm (s, PCI\({}_{6}\)\({}^{-}\)). **Oligodichlorophosphazene** [Cl-(PCI\({}_{2}\)=N)\({}_{\rm n}\)-PCI\({}_{3}\)]\({}^{+}\)[PCI\({}_{6}\)]\({}^{-}\), where n = 4-7, was synthesized via living cationic polymerization of Cl\({}_{3}\)P=NSiMe\({}_{3}\). A solution of Cl\({}_{3}\)P=NSiMe\({}_{3}\) (9.39 g, 48.02 mmol) in CH\({}_{2}\)Cl\({}_{2}\) (30 mL) was added dropwise to a solution of PCI\({}_{5}\) (2 g, 9.59 mmol) in CH\({}_{2}\)Cl\({}_{2}\) (50 mL) cooled to 0 \({}^{\circ}\)C in a three-necked flask. The reaction mixture was allowed to warm to room temperature and stirred with a magnetic stirrer. After complete conversion, confirmed by 31P NMR spectroscopy, all volatiles were removed under reduced pressure. Resulting light-yellow transparent viscous liquid was obtained in 6.58 g 91% yield. According to MALDI-TOF, the distribution of phosphazene homologs in the final mixture was as follows: four (24%), five (39%), six (29%) and seven (7%) -P=N- units with impurities content of not more than 0.5%. **Triphenoxyphosphoriphenyl** (PhO)\({}_{3}\)P=N-(PhO)\({}_{2}\)P=O, was purchased from Elortech, LLC and was used without purification, T\({}_{\rm m}\) = 73 \({}^{\circ}\)C, 31P NMR (CDCl\({}_{3}\)): \(\delta_{\rm P}\) = \(-\)15.6 ppm (d, \(-\)P=N-), \(\delta_{\rm P}\) = \(-\)21.7 ppm (d, \(-\)P=O). **Partial hydrolysis of [Cl\({}_{3}\)P=N-PCI\({}_{3}\)]\({}^{+}\)[PCI\({}_{6}\)]\({}^{-}\)**. A three-necked flask equipped with a magnetic stirrer was loaded with a solution of [Cl\({}_{3}\)P=N-PCI\({}_{3}\)]\({}^{+}\)[PCI\({}_{6}\)]\({}^{-}\) (1 g, 1.88 mmol) in dichloromethane (50 mL). Then freshly distilled water (67.7 mg, 3.76 mmol) was added dropwise. The reaction mixture was stirred at room temperature for 1 h. The solvent was removed under reduced pressure and the resulting mixture was analyzed by 31P NMR spectroscopy and consisted of Cl\({}_{3}\)P=N-POCI\({}_{2}\) and POCI\({}_{3}\). 31P NMR (CDC\({}_{3}\)): \(\delta_{\rm P}\) = \(-\)3.1 ppm (d, Cl\({}_{3}\)P=N-), \(\delta_{\rm P}\) = \(-\)11.6 ppm (d, \(-\)P(=O)Cl\({}_{2}\)), \(\delta_{\rm P}\) = 4.5 ppm (s, POCI\({}_{3}\)). The reaction between [Cl\({}_{3}\)P=N-PCI\({}_{3}\)]\({}^{+}\)[PCI\({}_{6}\)]\({}^{-}\)** and sodium trifluoroethylene** was carried out similarly to the aforementioned partial hydrolysis of monophosphazene salt. Synthesis of **2-ethylhexyl derivatives of imidophosphoric acids based on TCDP**. A three-necked flask equipped with a magnetic stirrer and a reflux condenser with a CaCl\({}_{2}\) tube was charged with a solution of TCDP (10.28 g, 0.038 mol) in dioxane (40 mL) and a solution of 2-ethylhexanol (29.8 g, 0.229 mol) in dioxane (50 mL). The reaction was carried out at 100 \({}^{\circ}\)C with stirring for 48 h with HCl purge with dry argon. At the end of the process, the solvent was distilled off using a rotary vacuum evaporator. The resulting liquid mass was dissolved in 150 mL of chloroform and repeatedly washed with distilled water in a separatory funnel. After vacuum distillation, the product was a clear, oily liquid with a yellow hue (21.1 g). Synthesis of **2-ethylhexyl derivatives of imidophosphoric acids based on oligodichlorophosphazene**.