## 3 Results and Discussion
It should be noted that along with the PPR, short linear oligophosphazenes are susceptible to an adverse reaction of an attacking agent with \(\alpha\)-carbon atoms of organic substituents, mainly those located at terminal units, resulting in the elimination of the side ether R-O-R and the formation of -O-Na+ fragments [43]. The subsequent replacement of the sodium atom by hydrogen during purification leads to the formation of -N=(RO)2P-OH groups, which proceeds further with PPR to yield the aminophosphonyl form -NH-(RO)2P=O. To show the equivalence of the structures obtained by nucleophilic substitution of chlorine atoms in the TCDP molecule and linear oligophosphazene, the reaction of the model shortest monophosphate [Cl3P=N-PCl3]+[PCl6]- was carried out and subsequent interaction of the latter with water and sodium alkoxide was studied. The composition of the reaction mixture was characterized by \({}^{31}\)P NMR spectroscopy. Partial hydrolysis of the phosphazene salt [Cl3P=N-PCl3]+[PCl6]- was carried out in dichloromethane media at room temperature. The molar ratio of phosphazene salt to H2O was 1:2 in order to replace one chlorine atom in the cation and to neutralize the counterion (Scheme 4). Hydrolysis leads to the ion pair destruction with the formation of the phosphorus oxychloride molecule. The system of doublets in the regions \(\delta_{\rm P}=-3.1\) and \(-11.6\) ppm in the \({}^{31}\)P NMR spectrum explicitly characterizes TCDP. The absence of signals of TCDP hydrolysis by-products in the spectrum indicates lower reactivity of phosphazophosphonyl compared with the monophosphazene salt. The same products (TCDP, POCl3) and trifluoroethyl chloride were yielded from the reaction of 1 mole of [Cl3P=N-PCl3]+[PCl6]- and 2 moles of sodium trifluoroethylate. In this case, the formation of the terminal phosphonyl group accompanied by trifluoroethyl chloride elimination (Scheme 5). Thus, the nucleophilic substitution of chlorine atoms in [Cl(PCI2=N)n-PCl3]+[PCl6]- oligomers with alkoxy fragments can be considered to be a method for the direct preparation of phosphazophosphonyls of a given length. Syntheses of EIPAs were carried out at 100 \({}^{\circ}\)C in dioxane (Schemes 6 and 7). Figure 3: The synthetic route to mono-substituted tetrachlorodiphosphonyl-N-(2-ethylhexyl)amine from TCDP. \({}^{31}\)P NMR spectra of the 2-ethylhexyl derivatives of oligophosphazenes EIPA-1 and EIPA-2 (Figure 3a,b) both contain a set of signals at 0 ppm, although the structures of the spectra are different. The \({}^{31}\)P NMR spectrum of EIPA-1 synthesized by TCDP with 2-ethylhexanol reaction (malor ratio 1:6) contains characteristic signals of three compounds (Figure 4): the singlet \(\delta_{\rm P}\) (CDCl\({}_{3}\), 25 \({}^{\circ}\)C) = 1.05 ppm of tetrakis(2-ethylhexyloxy)diphosphonylamine (**3**), two doublet signals in the \(\delta_{\rm P}\) range from 0.3 to 0.5 ppm characterizing hydroxy-tris(2-ethylhexyloxy)diphosphonyl-N-(2-ethylhexyl)amine (**4**), and the singlet \(\delta_{\rm P}\) = 0.1 ppm of dihydroxy-bis(2-ethylhexyloxy)phosphonyl-N-(2-ethylhexyl)amine (**5**). A small, broad signal at 0 ppm in the \({}^{31}\)P NMR spectrum of EIPA-2 showed a significant number of overlapping signals of the oligomers with different chain lengths. The significant broadening of the signals in the NMR spectra of PAPNA (Figure 3c) in comparison with EIPA-2 is obviously due to the wider molecular weight distribution of the first. The MALDI-TOF mass spectrum of EIPA-1 (Figure 5) is in a good agreement with the chemical structures of the products described above, determined by \({}^{31}\)P NMR spectroscopy. The main peaks with m/z 515 and 627 correspond to tri- (**5**) and tetra-substituted (**3** and **4**) derivatives of TCDP in protonated form, while the other peaks in the spectrum refer to complex dimer-type ions based on the represented molecules: 1029.1 ([**5** + **5**]H\({}^{+}\)), 1141.3 ([**5** + **3** or **4**]]H\({}^{+}\), 1275.6 ([**[**3** or **4**] + **3** or **4**]]Na\({}^{+}\)).