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Difficulty: HardChemistry in Daily Life and Industrial Applications

With reference to polymers and industrial materials widely used in daily life, consider the following statements:

1. Kevlar is a synthetic polyamide polymer exhibiting high tensile strength primarily due to extensive inter-chain hydrogen bonding.
2. Bakelite is a thermosetting polymer prepared through the condensation reaction of phenol with formaldehyde.
3. Polytetrafluoroethylene (Teflon) is classified as a thermosetting plastic because it repeatedly softens upon heating and can be easily remolded.

Which of the statements given above is/are correct?

  1. 1 and 2 onlyAnswer
  2. B
    2 and 3 only
  3. C
    1 and 3 only
  4. D
    1, 2 and 3

Answer

Statements 1 and 2 are correct, while Statement 3 is incorrect.
The option stating '1 and 2 only' is correct because Kevlar gains its extreme tensile strength from hydrogen bonding across parallel aromatic polyamide chains, and Bakelite is a classic thermosetting phenol-formaldehyde resin. Statement 3 is false because Teflon is a thermoplastic fluoropolymer, and thermosetting materials by definition undergo irreversible chemical hardening rather than repeated softening.

Step-by-Step Solution

1
Analyze Statement 1 regarding Kevlar structure and bonding.
Kevlar is an aromatic polyamide (aramid) made from 1,4-phenylene-diamine and terephthaloyl chloride. The alignment of aromatic rings and strong inter-chain hydrogen bonds between amide groups impart exceptionally high tensile strength. Statement 1 is correct.
Understanding polymer molecular interactions explains macroscopic mechanical properties.
2
Analyze Statement 2 regarding Bakelite synthesis.
Bakelite is synthesized via step-growth condensation of phenol with formaldehyde in the presence of an acid or base catalyst, yielding a highly cross-linked thermosetting resin. Statement 2 is correct.
Condensation polymerization of phenolic compounds forms rigid 3D networks.
3
Analyze Statement 3 regarding Teflon polymer classification.
Polytetrafluoroethylene (PTFE/Teflon) is a thermoplastic polymer, not a thermosetting plastic. Furthermore, thermosetting plastics undergo permanent cross-linking upon heating and cannot be remolded or softened again. Statement 3 is incorrect.
Thermoplastics soften on heating and harden on cooling, whereas thermosetting polymers permanently set.

Key Concept

Classification and Chemical Properties of Thermoplastic and Thermosetting Polymers
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Topics

Chemistry in Daily Life and Industrial Applications

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