Studies of Nitrogen—Phosphorus Compounds. XXIX. Synthesis and Thermal Stability of Phosphorus Diamide Nitride Resins

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The synthesis of resins by the reaction of trimeric or tetrameric phosphorus diamide nitride (NnPn(NH2)2n, n=3, 4) with formalin (CH2O), and the possibility of the formation of co-condensation resins through the addition of urea (CO(NH2)2) or melamine (C3H6N6) in the above reaction system have been investigated. Moreover, the thermal stability of resins has been studied by the DTA and TGA methods. In the NnPn(NH2)2n—CH2O system (n=3, 4), the rate of gelation increased with a decrease in pH, and remarkably accelerated with an increase in temperature. A mixture of these components in a suitable molar ratio was neutral and gelatinized gradually at 50°C within a period of 1—4 h. The gelatinous product was converted into a transparent resin at 80°C. The proper quantities of formalin were 7.5—9 and 16—20 mol to 1 mol of N3P3(NH2)6 and N4P4(NH2)8, respectively. The rate of gelation for the tetramer was distinctly greater than that of the trimer variety. In the N3P3(NH2)6—CO(NH2)2—CH2O and N3P3(NH2)6—C3H6N6—CH2O systems, the transparent resins were obtained in molar ratios of 1:2.5—10 and 1:1—20 of urea and melamine to the trimer variety, respectively. The resin of NnPn(NH2)2nCH2O system was found to be P 23—26%, and N 29—33%. The resin formed by the addition of urea or melamine naturally decreased the P content, while the N content did not vary appreciably. The thermal decomposition of resins reacted with NnPn(NH2)2n shifted more to the lower temperature side than did the urea—formalin and melamine—formalin resins. However, their carbonized residues formed remarkably, checked the spread of fire, and were incinerated at about 80°C.