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• SCH4U — Grade 12 Chemistry (Ontario)
• General Chemistry I
  • 1. Stoichiometry
  • 2. Aqueous Reactions
  • 3. Chemical Equations
    • 3.1 Balancing Equations
    • 3.2 Synthesis Reactions
    • 3.3 Decomposition Reactions
    • 3.4 Combustion Reactions
  • 4. Thermochemistry
  • 5. Atomic Structure
  • 6. Electronic Structure & Periodic Trends
  • 7. Chemical Bonding & Molecular Geometry
  • 8. Gases
  • 9. Liquids, Solids & Intermolecular Forces
  • 10. Solutions & Colligative Properties
  • 11. Gases & Atmospheric Chemistry
• General Chemistry II
  • 1. Reaction Kinetics & Rate Laws
  • 2. Chemical Equilibrium
  • 3. Acids, Bases, and Buffers
  • 4. Electrochemistry & Redox Cells
  • 5. Thermodynamics
  • 6. Solubility & the Solubility Product
  • 7. Nuclear Chemistry
  • 8. Coordination Chemistry
• Organic Chemistry I
  • 1. Nomenclature & Functional Groups
  • 2. Stereochemistry & Isomerism
  • 3. Substitution and Elimination
  • 4. Structure & Bonding in Organic Molecules
  • 5. Alkenes
  • 6. Alkynes
  • 7. Alcohols & Ethers
  • 8. Spectroscopy
  • 9. Polymers
• Organic Chemistry II
  • 1. Aromatic Chemistry
  • 2. Aldehydes & Ketones
  • 3. Carboxylic Acids & Derivatives
  • 4. Enolates & the Aldol Reaction
  • 5. Amines
  • 6. Conjugated Systems & Diels-Alder
  • 7. Biomolecules
  • 8. Synthesis Strategy & Retrosynthesis

9. Polymers

Polymers are giant molecules built by repeating a small unit — the monomer — hundreds or thousands of times. Plastics, rubber, nylon, proteins, and DNA are all polymers; the two ways to build them are addition and condensation.

Addition Polymerization

Alkenes add across their double bonds, usually by a radical mechanism, with no atoms lost. The repeat unit is the monomer with its double bond opened.

• Polypropylene: from propene — packaging, car parts.
• Polystyrene: from styrene — foam cups, insulation.
• PVC: from vinyl chloride — pipes, window frames.
• Teflon (PTFE): from tetrafluoroethylene — non-stick coatings.

Condensation Polymerization

Two monomers join with the loss of a small molecule (usually water). Each monomer needs two functional groups.

Properties and Recycling

Chain length, branching, and cross-linking set a polymer's strength and melting behaviour. Thermoplastics (polyethylene, PET) soften on heating and can be recycled; thermosets (epoxy, Bakelite) are cross-linked and cannot be remelted. Recycling codes 1–7 identify the plastic type.

Practice Problems

1. Draw the repeat unit of polypropylene, made from CH₂=CH–CH₃.
2. Is the formation of nylon 6,6 an addition or condensation polymerization? What small molecule is lost?
3. Why is LDPE flexible while HDPE is rigid?
4. Name the monomers of PET.

Answers: 1. –(CH₂–CH(CH₃))–   2. Condensation — water   3. LDPE chains are branched and can't pack tightly; HDPE chains are linear and pack closely   4. Terephthalic acid and ethylene glycol