Alexandra Matthews

• Materials

  Chemical or mixture of chemicals
• Examples of materials


  • Metals
  • Ceramics
  • Polymers
• Sources of materials


  • Living things (cotton, wool, silk, leather, wood)
  • Non-living things (limestone, metals)
  • Synthetic (polymers from oil, paper from cellulose)
• Important properties of materials

  • Melting point
  • Tensile strength
  • Strength in compression
  • Stiffness
  • Hardness
  • Flexibility
  • Density
• Hydrocarbon


  Made from carbon and hydrogen, can be used to make synthetic polymers
• How polymers are made

  Monomers joined together through polymerisation
• Polymers


  • Very long molecules
  • Made when many small molecules (monomers) are joined together
• Shorter polymer molecules (e.g. wax)

  Lower melting point than longer polymer molecules (e.g. polythene)
• Longer polymer chains


  Polymer is stronger
• Adding cross-links


  Polymer is harder, stronger and less flexible
• Adding plasticisers


  Polymer is more flexible and softer
• Increasing crystallinity by lining up polymer molecules


  Polymer is stronger and denser
• Hydrocarbons from oil are used as fuels and to make chemicals/plastics
• Monomer


  Small molecule that joins together to form a polymer
• Polymerisation


  Chemical reaction to join monomers into a polymer
• Polythene is made by polymerisation of ethene molecules
• Polypropene is made by polymerisation of propene molecules
• Nylon is made by addition polymerisation
• Plastics


  • Insulators
  • Unreactive
  • Light
  • Hard to break
  • Strong
  • Reasonably fireproof
• Adding a plasticiser


  Makes the polymer more flexible
• Lengthening the polymer chain

  Increases the melting point
• Little cross-linking between chains


  Polymer can be reshaped many times when heated
• Heavy cross-linking


  Polymer cannot be reshaped when heated, may eventually burn
• High-density polythene

  Hard and strong, used for bowls
• Low-density polythene


  More flexible, used for plastic bags
• Plastics are useful but can be problematic for disposal
• Polymer

  Many units joined together in a long chain
• Natural polymers

  • DNA
  • Starch
  • Cellulose
• Macromolecule

  Very large molecule made up of many monomers
• Polymerisation reaction

  Reaction where monomers join together to form a polymer
• Natural polymers in the body

  • Keratin (hair, nails, horns)
  • Collagen (skin, bones)
• Properties of a polymer depend on length of chain, monomer used, and conditions of polymerisation