--- title: "Polythiazyl preparation; polyphosphazene, chalcogenide uses" subject: "Engineering Chemistry" chapter: 4 key: "semester_2/engineering_chemistry:polythiazyl-polyphosphazene" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/polythiazyl-polyphosphazene site: BCT Engineering --- # Polythiazyl preparation; polyphosphazene, chalcogenide uses Engineering Chemistry · Chapter 4: Engineering Polymers - Asked in: 2072 Magh, 2+3 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/polythiazyl-polyphosphazene - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-4 ## Question Write the preparation of polythiazyl. Mention the applications of Polyphosphazenes and Chalcogenide glasses in engineering fields. ## Short answer Polythiazyl (SN)x prepared by passing S4N4 vapour over hot silver wool, giving S2N2 that polymerises at room temperature. Polyphosphazenes: flameresistant elastomers, O-rings, fuel hoses, biomedical implants, solid electrolytes. Calcogenide glasses: IR optics, phase-change memory, photocopiers. ## Answer #### Preparation of polythiazyl **Polythiazyl (polymeric sulphur nitride), (SN)ₓ.** Preparation: 1. S₄N₄ is made by passing NH₃ into a solution of S₂Cl₂ (6S₂Cl₂ + 16NH₃ → S₄N₄ + 8S + 12NH₄Cl). 2. S₄N₄ vapour is passed over hot silver wool at 250–300 °C to give S₂N₂ crystals: S₄N₄ → 2S₂N₂ (Ag). 3. S₂N₂ polymerises in the solid state at room temperature: n S₂N₂ → 2 (SN)ₙ (golden, lustrous fibres). Structure: chains of alternating S and N atoms, –S=N–S=N–. (SN)ₓ conducts electricity like a metal along the chain direction and becomes superconducting at about 0.3 K. Uses: an example of a conducting polymer without carbon, used in studies of one-dimensional conductors, microelectronic and photoconducting devices. #### Applications of polyphosphazenes - Flame-resistant and non-burning materials and coatings. - Elastomers (fluoroalkoxy phosphazene rubber) that stay flexible from –60 °C to 180 °C: seals, O-rings, fuel hoses and gaskets in aircraft and the oil industry. - Biomedical uses: biodegradable implants, drug delivery, artificial skin, dental materials. - Solid polymer electrolytes for lithium batteries; membranes for gas separation. - Water-repellent coatings, lubricants, hydraulic fluids and low-temperature insulation. #### Applications of chalcogenide glasses - Infrared optics: lenses, windows, thermal imaging and night vision. - IR optical fibres; phase-change memory (rewritable discs); photoreceptors of photocopiers; switches and sensors. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is S4N4 made for polythiazyl? A. Passing NH3 into S2Cl2 solution B. Burning S in N2 C. Heating SO2 with NH4Cl D. Mixing S and N2 at room temperature Answer: A. 6S2Cl2 + 16NH3 gives S4N4 + 8S + 12NH4Cl. (Key point: S4N4 preparation) 2. What is the role of hot silver wool? A. S4N4 vapour passes over it at 250-300 C to give S2N2 B. It oxidises S to SO2 C. It forms (SN)x directly in liquid D. It absorbs NH3 Answer: A. S4N4 becomes S2N2 over hot silver, then S2N2 polymerises to (SN)x. (Key point: Conversion to S2N2) 3. What is special about (SN)x? A. It is an insulator B. It conducts like a metal along chains and is superconducting near 0.3 K C. It is flammable D. It is a rubber Answer: B. It is a carbon-free conducting polymer. (Key point: Property of (SN)x) 4. Which use applies to polyphosphazenes? A. Flame-resistant materials and elastomer seals flexible from -60 to 180 C B. Explosives C. Photocopier drums D. Edible films Answer: A. They are flame-resistant, used in flexible elastomers, biomedical materials and polymer electrolytes. 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