- 2068 Bhadra · 2.5 marks
Silicone rubbers: preparation and applications
Short answer
Silicone rubbers are prepared by hydrolysis of dimethyldichlorosilane to polydimethylsiloxane, then vulcanised with peroxide. They maintain elasticity from −50 to 250 °C, used for gaskets, seals, medical tubing, and electrical insulation.
Give the preparation and applications of silicone rubbers.
Preparation
- Dimethyldichlorosilane is prepared: Si + 2CH₃Cl → (CH₃)₂SiCl₂ (Cu, 300 °C).
- Hydrolysis and condensation give long linear polydimethylsiloxane chains of very high molecular mass: (CH₃)₂SiCl₂ + 2H₂O → (CH₃)₂Si(OH)₂ + 2HCl n (CH₃)₂Si(OH)₂ → [–Si(CH₃)₂–O–]ₙ + n H₂O
- The polymer is mixed with a filler (silica) and vulcanised (cross-linked) by heating with a peroxide such as benzoyl peroxide, giving a flexible rubbery network.
Applications
Silicone rubbers keep their elasticity from about –50 °C to 250 °C and resist oxidation, ozone, water and chemicals.
- Gaskets, seals, O-rings and hoses for aircraft and engines.
- Insulation of electrical wires and cables; keypads of electronic devices.
- Medical tubing, catheters, implants; baby bottle nipples.
- Sealants for building and electronics, bakeware and kitchen moulds.
✓ Answer checked by Claude Opus 5.5 (high effort)
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