JEE Main 2020 · 5 September · evening · Single correct · +4 / −1
Which one of the following polymers is not obtained by condensation polymerisation?
- (a) Bakelite
- (b) Nylon 6
- (c) Buna-N
- (d) Nylon 6, 6
Answer and solution
Answer (c) Buna-N
Solution
Chemistry ma’am · 3 steps
Ask what the monomers lose when they link up. If nothing is lost, it is addition polymerisation.
- Two kinds. In condensation polymerisation, the monomers join through functional groups and lose a small molecule such as H₂O each time. In addition polymerisation, monomers with C=C double bonds open up and join, and nothing is lost.
Polymer Monomers Small molecule lost Type Bakelite phenol C₆H₅OH and formaldehyde HCHO H₂O condensation Nylon 6 caprolactam, heated with water to open the ring into 6-aminohexanoic acid H₂O condensation Buna-N 1,3-butadiene CH₂=CH-CH=CH₂ and acrylonitrile CH₂=CH-CN none addition (copolymer) Nylon 6, 6 H₂N(CH₂)₆NH₂ and adipic acid HOOC(CH₂)₄COOH H₂O condensation - Buna-N. Both monomers of Buna-N have C=C bonds and no -OH, -COOH or -NH₂ groups to condense. They join by free-radical addition, so the polymer has exactly the atoms of the monomers.
- So. Buna-N, option (c), is the one polymer here that is not made by condensation polymerisation.
The idea to keep. Look at the monomers. C=C bonds with no reactive end groups point to addition. Pairs of groups like -COOH with -NH₂ or -OH that lose water point to condensation.
Answer from the NTA final answer key. Solution by PrepWiser.