Question

Which of the following is/are thermosetting polymer/s ?

1. Teflon
2. Bakelite
3. Polypropylene
4. Polystyrene

• A. i and ii
• B. iii and iv
• C. Only i
• D. Only ii

Answer 1

Answer:

D. Only ii

• Thermosetting polymers are synthetic materials that undergo a chemical reaction during processing, known as curing, which creates a permanent, three-dimensional cross-linked network. Once shaped and hardened, they cannot be reshaped or remelted by heating.
• Bakelite (Phenol-Formaldehyde Resin): It was the first synthetic plastic invented by Leo Baekeland in 1907. It is highly resistant to heat, electricity, and chemical solvents, making it ideal for electrical insulators, radio housings, and kitchenware handles.
• Comparison with Thermoplastics: Unlike thermosets, Teflon (Polytetrafluoroethylene), Polypropylene, and Polystyrene are classified as thermoplastics. These can be repeatedly softened by heating and hardened by cooling, allowing them to be recycled and reshaped multiple times.
• Key Distinctions:
  • Thermosets: Bakelite, Epoxy resins, Melamine-formaldehyde, Vulcanized rubber.
  • Thermoplastics: Polyethylene (PE), Polypropylene (PP), Polystyrene (PS), Polyvinyl chloride (PVC), and Polytetrafluoroethylene (PTFE/Teflon).
• Structural Significance: The primary difference lies in the bonding; thermoplastics rely on weak intermolecular forces (Van der Waals forces) between polymer chains, while thermosets are characterized by strong covalent bonds forming a rigid grid structure.