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Polyphosphonitrilic chloride preparation and uses

Short answer

Polyphosphonitrilic chloride is prepared by heating PCl5 with NH4Cl at 120–150 °C to give cyclic trimer (NPCl2)3, then heating this at 250 °C yields the linear polymer (NPCl2)n. It is used as a precursor for polyorganophosphazenes, flame retardants, and derivatives for fire-resistant elastomers and biomedical materials.

Write the preparation and uses of polyphosphonitrilic chloride.

Preparation

Phosphonitrilic compounds (phosphazenes) contain the –N=PX₂– unit (X = Cl, F, Br, OR, NR₂) and are formed as cyclic oligomers (NPX₂)₃, (NPX₂)₄ and long chain polymers (NPX₂)ₙ.

Preparation of phosphonitrilic chloride

  1. Phosphorus pentachloride is heated with ammonium chloride at about 120–150 °C in a solvent (chlorobenzene or sym-tetrachloroethane): n PCl₅ + n NH₄Cl → (NPCl₂)ₙ + 4n HCl The main product is the cyclic trimer (NPCl₂)₃ with some tetramer.
  2. On heating the trimer at about 250 °C in a vacuum (or sealed tube), ring-opening polymerisation gives the high polymer, polydichlorophosphazene (NPCl₂)ₙ, a rubber-like substance called "inorganic rubber".
        N
     /     \
  Cl₂P       PCl₂      (NPCl₂)₃ trimer:
     |       |         six-membered ring of
     N       N         alternating N and P
      \     /
       PCl₂

Uses

  • It is the starting material for polyorganophosphazenes: the Cl atoms are replaced by OR, NHR or OCH₂CF₃ groups, which give stable, useful polymers.
  • Used directly as an inorganic rubber (hydrolytically unstable, so its use is limited) and as a flame retardant.
  • Its derivatives are used as fire-resistant materials, elastomers for seals and hoses, biomedical materials, membranes and solid polymer electrolytes.

✓ Answer checked by Claude Opus 5.5 (high effort)

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