Organic Chemistry - Polymers

This note covers the definition of polymers, types of polymerization (addition and condensation), examples of natural and synthetic polymers, properties and uses of common polymers, environmental impacts of plastics, recycling methods, and social, economic, and environmental considerations.

1. Definition of Polymers
  • 🔹 Polymer:

    🔹 A large molecule (macromolecule) made up of repeating smaller units called monomers.

  • 🔹 Monomer → Polymer:

    🔹 Monomers chemically bond together to form long chains.

  • 🔹 Examples:

    🔹 Natural: proteins, cellulose; Synthetic: poly(ethene), nylon

2. Formation of Poly(ethene)
  • 🔹 Type:

    🔹 Addition polymerization

  • 🔹 Monomer:

    🔹 Ethene (C₂H₄)

  • 🔹 Mechanism:
    • 🔹 Initiation:

      🔹 Free radicals open the double bond in ethene.

    • 🔹 Propagation:

      🔹 Monomers join the growing chain via repeated addition.

    • 🔹 Termination:

      🔹 Chain growth stops when radicals combine or are neutralized.

  • 🔹 Uses:
    • 🔹 LDPE:

      🔹 Plastic bags, clingfilm, bottles

    • 🔹 HDPE:

      🔹 Pipes, containers, toys

  • 🔹 Advantages:

    🔹 Light, flexible, chemically inert, waterproof

3. Structure of Polymers from Monomers
  • 🔹 Steps:
    • 🔹 Identify the reactive bond (usually C=C for addition polymers).
    • 🔹 Repeat the monomer unit in a chain, removing the double bond.
    • 🔹 Enclose the repeating unit in brackets with subscript n.
  • 🔹 Example:
    • 🔹 Monomer:

      🔹 CH₂=CHCl

    • 🔹 Polymer:

      🔹 [-CH₂-CHCl-]ₙ

4. Condensation Polymers
  • 🔹 Definition:

    🔹 Formed by condensation reactions where two monomers react and release a small molecule (water or HCl).

  • 🔹 Examples:
    • 🔹 Nylon (polyamide):
      • 🔹 Monomers:

        🔹 Hexane-1,6-diamine + Hexanedioic acid

      • 🔹 Reaction:

        🔹 Forms [-NH-(CH₂)₆-NH-CO-(CH₂)₄-CO-]ₙ + 2nH₂O

      • 🔹 Uses:

        🔹 Clothing, ropes, parachutes

    • 🔹 Terylene (polyester):
      • 🔹 Monomers:

        🔹 Ethane-1,2-diol + Benzene-1,4-dicarboxylic acid

      • 🔹 Reaction:

        🔹 Forms [-O-CH₂-CH₂-O-CO-C₆H₄-CO-]ₙ + 2nH₂O

      • 🔹 Uses:

        🔹 Fabrics, clothing, industrial fibers

5. Uses of Man-Made Fibers
  • 🔹 Properties:

    🔹 Strong, durable, resistant to wear, washable

  • 🔹 Examples:
    • 🔹 Nylon:

      🔹 Clothing, ropes, toothbrush bristles, parachutes

    • 🔹 Terylene:

      🔹 Clothing, curtains, seat belts, industrial fabrics

6. Pollution Problems from Non-Biodegradable Plastics
  • 🔹 Examples:

    🔹 Poly(ethene), nylon, Terylene

  • 🔹 Problems:
    • 🔹 Landfill accumulation
    • 🔹 Harm to wildlife (ingestion, entanglement)
    • 🔹 Blocked drainage → flooding
    • 🔹 Toxic fumes when burned
7. Recycling of Plastics
  • 🔹 Physical (Mechanical) Recycling:

    🔹 Sorting → washing → shredding → melting → remolding. Example: Plastic bottles → new containers. Limitation: properties may degrade after repeated recycling.

  • 🔹 Chemical (Depolymerization) Recycling:

    🔹 Plastics broken down into monomers. Example: Polyesters depolymerized using acid catalysts to recover monomers. Advantage: monomers can be reused to make new high-quality polymers.

8. Social, Economic, and Environmental Issues
  • 🔹 Social:

    🔹 Public awareness campaigns; inconvenience of sorting waste

  • 🔹 Economic:

    🔹 Costly collection, transportation, processing; chemical recycling more expensive

  • 🔹 Environmental:

    🔹 Reduces landfill and pollution; energy consumption; some chemical processes may produce hazardous waste

  • 🔹 Addition polymerization of ethene: nCH₂=CH₂ → [-CH₂-CH₂-]ₙ
  • 🔹 Addition polymerization of chloroethene: nCH₂=CHCl → [-CH₂-CHCl-]ₙ
  • 🔹 Condensation polymerization - Nylon (polyamide): nH₂N-(CH₂)₆-NH₂ + nHOOC-(CH₂)₄-COOH → [-NH-(CH₂)₆-NH-CO-(CH₂)₄-CO-]ₙ + 2nH₂O
  • 🔹 Condensation polymerization - Terylene (polyester): nHO-CH₂-CH₂-OH + nHOOC-C₆H₄-COOH → [-O-CH₂-CH₂-O-CO-C₆H₄-CO-]ₙ + 2nH₂O
  • 🔹 Decomposition of polyesters (chemical recycling): [-O-CH₂-CH₂-O-CO-C₆H₄-CO-]ₙ + acid → HO-CH₂-CH₂-OH + HOOC-C₆H₄-COOH

  • ⚠️ All polymers are synthetic; natural polymers exist too.
  • ⚠️ Addition and condensation polymerization are the same.
  • ⚠️ Polymerization always produces water; this only occurs in condensation polymerization.
  • ⚠️ Recycling always restores the original quality of the plastic.
  • ⚠️ Non-biodegradable plastics are harmless because they don’t decay quickly.

  • 👉 Always show repeating units with brackets and subscript n.
  • 👉 Distinguish addition (double bond, no small molecule released) vs condensation polymerization (-OH/-COOH or -NH₂/-COOH, water released).
  • 👉 Be able to label polymers and their monomers in diagrams.
  • 👉 Use full names of monomers in condensation polymer equations.
  • 👉 For environmental questions, include social, economic, and environmental perspectives.
  • 👉 Remember the uses and properties of LDPE, HDPE, Nylon, and Terylene.

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