---
title: "Short note: Polyphosphazines"
subject: "Engineering Chemistry"
chapter: 4
key: "semester_2/engineering_chemistry:polyphosphazines-short-note"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/polyphosphazines-short-note
site: BCT Engineering
---

# Short note: Polyphosphazines

Engineering Chemistry · Chapter 4: Engineering Polymers

- Asked in: 2069 Bhadra, 2 marks
- Video: [Phosphazenes classification, Preparation, Properties and Structure | simplified](https://www.youtube.com/watch?v=1xdzLBv85GM) — Bholanath Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/polyphosphazines-short-note
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-4

## Question

Write a short note on polyphosphazines.

## Short answer

Polyphosphazenes have a P–N backbone with two substituents on P, prepared by ring-opening polymerisation of (NPCl2)3 and substituting Cl with alkoxy or amino groups. They stay flexible at low temperatures, are flame retardant, and are used for seals, fuel hoses and biomedical implants.

## Answer

**Polyphosphazenes (polyphosphazines)** are inorganic polymers with a backbone of alternating phosphorus and nitrogen atoms, –[N=PR₂]ₙ–, with two organic or other groups (R = OR, NHR, F) on each phosphorus.

**Preparation:** 3PCl₅ + 3NH₄Cl → (NPCl₂)₃ (cyclic trimer) + 12HCl; ring-opening polymerisation of the trimer at 250 °C gives (NPCl₂)ₙ; then the Cl atoms are replaced using NaOR or amines, e.g. (NPCl₂)ₙ + 2n NaOCH₃ → [NP(OCH₃)₂]ₙ + 2n NaCl.

**Properties and uses:** polyphosphazenes stay flexible even at very low temperatures, are flame retardant and are chemically resistant. They are used for seals and O-rings, fuel hoses, biomedical implants and solid electrolytes.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What forms the backbone of polyphosphazenes?
   A. Alternating silicon and oxygen atoms
   B. Carbon–carbon chain
   C. Alternating sulphur and nitrogen atoms
   D. Alternating phosphorus and nitrogen atoms
   Answer: D. Polyphosphazenes have an –[N=PR2]n– backbone. (Key point: Backbone)

2. In making polyphosphazenes, what is the role of NaOR or amines?
   A. They replace Cl atoms in (NPCl2)n to give stable polymers
   B. They open the S8 ring
   C. They act as the source of phosphorus
   D. They polymerise the trimer at 250 °C
   Answer: A. Substituting reactive P–Cl bonds with OR or NHR groups stabilises the polymer. (Key point: Preparation)

3. Which combination describes polyphosphazene properties?
   A. Brittle, flammable, soluble in water
   B. Flexible at low temperature, flame retardant, chemically resistant
   C. Rigid, conducting, magnetic
   D. Biodegradable by bacteria within days
   Answer: B. These properties lead to seals, O-rings, fuel hoses and implants. (Key point: Properties)