--- title: "Linear chain polymer; sulphur-based inorganic polymers" subject: "Engineering Chemistry" chapter: 4 key: "semester_2/engineering_chemistry:linear-polymer-sulphur-inorganic" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/linear-polymer-sulphur-inorganic site: BCT Engineering --- # Linear chain polymer; sulphur-based inorganic polymers Engineering Chemistry · Chapter 4: Engineering Polymers - Asked in: 2067 Chaitra, 1+4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/linear-polymer-sulphur-inorganic - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-4 ## Question What is linear chain polymer? Write the preparation and uses of different types of sulphur bases inorganic polymers. ## Short answer Linear chain polymers have monomers linked end‑to‑end without branches, thermoplastic and soluble. Sulphur‑based polymers: plastic sulphur from heated S8 quenched; vulcanised rubber with S–S cross‑links; Thiokol from ethylene dichloride and Na2S4; (SN)n by polymerising S2N2, a metallic conductor. Used in tyres, sealants, and microelectronics. ## Answer #### Linear chain polymer A **linear chain polymer** has its monomer units joined end to end in a long, straight, unbranched chain with no cross-links. Such polymers are generally thermoplastic, soft or flexible, soluble and recyclable. Examples: high-density polyethylene, PVC, nylon, plastic sulphur. #### Sulphur-based inorganic polymers: preparation and uses **Plastic (polymeric) 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. S₈ → (heat above 160 °C) → ·S–S–S...S–S· (chain) → quench in water → plastic sulphur **Cross-linked sulphur polymers.** In vulcanisation, a small amount of sulphur forms –S–S– cross-links between rubber chains, which hardens the rubber (used for tyres). Polysulphide rubber (**Thiokol**) is obtained from ethylene dichloride and sodium polysulphide: n ClCH₂CH₂Cl + n Na₂S₄ → [–CH₂CH₂–S₄–]ₙ + 2n NaCl. **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: it is an example of a conducting polymer without carbon, used in studies of one-dimensional conductors and in microelectronic and photoconducting devices. Uses of the sulphur-based polymers: vulcanised rubber for tyres and belts, Thiokol sealants and fuel hoses, sulphur concrete, and (SN)ₓ in conducting and microelectronic devices. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a linear chain polymer? A. Monomer units joined end to end in an unbranched chain without cross-links B. A 3-D network with many cross-links C. A ring of S8 D. A branched network Answer: A. Linear polymers are usually thermoplastic, soluble and recyclable. (Key point: Linear chain) 2. Plastic sulphur forms when A. Sulphur is cooled slowly to room temperature B. Sulphur heated above 160 °C is quenched in cold water C. S4N4 reacts with silver D. Rubber is vulcanised Answer: B. Chains are frozen into a brown elastic solid. (Key point: Plastic sulphur) 3. What is the correct route to (SN)x? A. S8 plus NH3 gives (SN)x directly B. S2Cl2 + PCl5 C. S4N4 over hot silver wool gives S2N2, which polymerises in solid state D. S4N4 is quenched in water Answer: C. S2N2 crystals polymerise at room temperature to golden fibres. (Key point: Polythiazyl route) 4. Which uses sulphur-based polymers correctly? A. Thiokol for aircraft wings B. (SN)x as insulator C. Plastic sulphur as hard glass D. Vulcanised rubber for tyres and Thiokol sealants and fuel hoses Answer: D. Sulphur cross-links harden rubber; Thiokol resists oil and solvents. 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