Question
Classify the following polymers as addition or condensation, and as homopolymer or copolymer: (a) Nylon 6,6, (b) Polythene, (c) Bakelite, (d) Buna-S.
Solution — Step by Step
Made by condensation polymerisation of hexamethylenediamine and adipic acid. Two different monomers → copolymer. Water is eliminated during each linkage formation.
Type: condensation copolymer.
Made by addition polymerisation of ethene (). Single monomer → homopolymer. No small molecule eliminated.
Type: addition homopolymer.
Made by condensation of phenol and formaldehyde. Two different monomers → copolymer. Water is eliminated.
Type: condensation copolymer.
Made by addition (free-radical) copolymerisation of butadiene and styrene. Two different monomers → copolymer. No elimination.
Type: addition copolymer.
Final answers:
- Nylon 6,6: condensation copolymer
- Polythene: addition homopolymer
- Bakelite: condensation copolymer
- Buna-S: addition copolymer
Why This Works
Polymerisation type depends on monomer structure. Addition uses unsaturated monomers ( or ) — they open up and chain together with no byproduct. Condensation uses bifunctional monomers (like diols + diacids) and eliminates a small molecule (water, HCl, etc.).
Homopolymer vs copolymer is purely about the number of monomer types — one type gives a homopolymer regardless of mechanism.
Alternative Method
Use the structural approach. If the repeat unit shows an amide () or ester () linkage that wasn’t in the monomer, it’s condensation. If the repeat unit looks like the monomer minus a double bond, it’s addition.
For NEET, memorise the four classic copolymers: nylon 6,6 (condensation), Buna-N (addition), Buna-S (addition), Bakelite (condensation). The exam picks from this list.
Common Mistake
Calling nylon 6 (made from caprolactam alone) a copolymer. It’s a homopolymer because there’s only one monomer, despite being a condensation polymer. Don’t confuse the two classifications.