Describe and draw the structure of: (a) nylon, a polyamide (b) PET, a polyester

Organic Chemistry – Polymers

1️⃣ Nylon – A Polyamide

Nylon is a synthetic polymer that behaves like a long chain of Lego bricks. Each brick is a monomer unit that links together to form a strong, flexible material used in everything from clothes to ropes. 🧱🔗

MonomerReactionRepeating Unit
Hexamethylenediamine (H₂N-(CH₂)₆-NH₂)Condensation with Adipic Acid (HOOC-(CH₂)₄-COOH)\$\ce{[-NH-(CH2)6-CO-]}_n\$
Adipic AcidCondensation with HexamethylenediamineSame as above

How it forms:

  1. Hexamethylenediamine and adipic acid react, releasing water (a condensation reaction).

  2. Each time a water molecule leaves, a new amide bond (–NH–CO–) is formed.

  3. Repeating this many times creates a long nylon chain.

Key features:

  • Strong and flexible – like a rubber band that can stretch but not break easily.

  • Heat-resistant – can be worn as a jacket in hot weather.

  • Water-resistant – keeps you dry in the rain.

2️⃣ PET – A Polyester

Polyethylene terephthalate (PET) is the polymer that makes many plastic bottles and polyester clothing. Think of PET as a chain of tiny “sugar” units linked together, giving it a sweet, strong structure. 🍬🔗

MonomerReactionRepeating Unit
Ethylene Glycol (HO-CH₂-CH₂-OH)Condensation with Terephthalic Acid (HOOC-C₆H₄-COOH)\$\ce{[-O-CH2-CH2-O-CO-C6H4-CO-]}_n\$
Terephthalic AcidCondensation with Ethylene GlycolSame as above

How it forms:

  1. Ethylene glycol and terephthalic acid react, releasing water.

  2. Each water loss creates an ester bond (–O–CO–).

  3. Repeating this builds a long PET chain.

Key features:

  • Strong and lightweight – perfect for bottles that can hold water without breaking.

  • Transparent and shiny – gives that “new bottle” look.

  • Recyclable – can be turned into new bottles or clothing.

Quick comparison:

PropertyNylonPET
Main bondAmide (–NH–CO–)Ester (–O–CO–)
Common useClothing, ropes, carpetsPlastic bottles, polyester fabrics
Heat resistanceHigh – can be used in high‑temperature environmentsModerate – melts at ~260 °C

Remember: Both nylon and PET are made by linking small molecules (monomers) together through a condensation reaction that removes water. The repeating units give each polymer its unique properties, just like how different Lego bricks create different structures. Happy polymerising! 🚀