---
title: "Short note: Sulphur based polymers"
subject: "Engineering Chemistry"
chapter: 4
key: "semester_2/engineering_chemistry:sulphur-based-polymers"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/sulphur-based-polymers
site: BCT Engineering
---

# Short note: Sulphur based polymers

Engineering Chemistry · Chapter 4: Engineering Polymers

- Asked in: 2069 Bhadra, 3 marks
- Video: [Polymer Chemistry||Polymer of Sulphur in Hindi/Urdu|| lecture 7](https://www.youtube.com/watch?v=GWl8G0FVzds) — SHERENATE 🪄
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/sulphur-based-polymers
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-4

## Question

Write a short note on sulphur based polymers.

## Short answer

Sulphur-based inorganic polymers include plastic sulphur (quenched from melt, rubbery chains), polythiazyl (SN)x (metallic conductor), and polysulphide rubber (Thiokol) made from ClCH2CH2Cl and Na2S4. Thiokol resists oils and solvents, used for sealants and hoses.

## Answer

Sulphur forms inorganic polymers because S atoms can catenate (S–S bonds) and link with N.

1. **Plastic sulphur:** Ordinary rhombic sulphur has S₈ rings. When sulphur is heated above about 160 °C, the rings open and join into long chains (S)ₙ, and the liquid becomes very viscous. If this hot liquid (heated to near its boiling point) is poured into cold water, the chains are frozen as a brown, rubber-like, elastic solid called **plastic sulphur**. It slowly reverts to the S₈ form.
2. **Polythiazyl (SN)ₓ:** a chain polymer of alternating S and N, made by polymerising S₂N₂ (from S₄N₄ over hot silver wool); a metal-like conductor and a superconductor at about 0.3 K.
3. **Polysulphide rubber (Thiokol):** n ClCH₂CH₂Cl + n Na₂S₄ → [–CH₂CH₂–S₄–]ₙ + 2n NaCl; oil and solvent resistant, used for sealants, gaskets and fuel hoses.
4. **Sulphur network (chalcogenide) glasses** such as As₂S₃ for infrared optics.

Sulphur cross-links also vulcanise rubber.

## Check yourself

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

1. How is plastic sulphur made?
   A. Sulphur is heated above about 160 °C and the hot liquid is poured into cold water
   B. Rhombic sulphur is dissolved in water
   C. S8 is burnt in air
   D. S4N4 is passed over silver wool
   Answer: A. Heating opens S8 rings into chains; quenching in cold water freezes them as a rubber-like solid. (Key point: Plastic sulphur)

2. What is notable about polythiazyl (SN)x?
   A. It is a perfect insulator
   B. It is a metal-like conductor and a superconductor at about 0.3 K
   C. It is made from S8 and carbon
   D. It dissolves in oil as a lubricant
   Answer: B. (SN)x is a chain of alternating S and N that conducts like a metal. (Key point: Polythiazyl)

3. Which reaction gives polysulphide rubber (Thiokol)?
   A. Si + CH3Cl
   B. PCl5 + NH4Cl
   C. ClCH2CH2Cl + Na2S4
   D. Phenol + HCHO
   Answer: C. Ethylene dichloride and sodium polysulphide give [–CH2CH2–S4–]n and NaCl. (Key point: Thiokol)

## Related in Engineering Chemistry

- [Linear chain polymer; sulphur-based inorganic polymers](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alinear-polymer-sulphur-inorganic) — Engineering Chemistry, chapter 4
- [Chalcogenide glasses and network polymers of sulphur](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Achalcogenide-glass-polymers) — Engineering Chemistry, chapter 4