Structure and properties of polymers

Chemical Ideas 5.6.

OCR Salters B F332

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Addition polymerisation:

  • If the monomers (represented by the letter A) contain a double bond, they can add together to make a polymer.
  • A + A + A + A  ->  -A-A-A-A-
  • No other products are formed.
  • The polymer structure can be represented more simply by drawing the repeating unit.


  • A co-polymer is made when two different monomers (represented by the letters A and B) beomce incorporated into the polymer chain.
  • A + B + A + B  ->  -A-B-A-B-
  • No other products are formed.
  • The polymer structure can be represented more simply by drawing the repeating unit.
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Properties of polymers

Chain length:

  • the longer the chains, the stronger the polymer
  • tensile strength increases because:
    • longer chains become more entangled
    • longer chains have stronger intermolecular bonds between them

Side groups on the polymer chain:

  • the more polar the side groups, the stronger the bonds between polymer chains, so the polymer is stronger


  • straight, unbranched polymer chains can pack closer together, allowing stronger bonds between the chains, so the polymer is stronger
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Properties of polymers, continued

Chain flexibility:

  • the more rigid the chain, the stronger the polymer
  • hydrocarbon chains are very flexible, whereas incorporating benzene rings makes the polymer chains stiffer


  • more extensive cross-linking makes the polymer harder to melt


  • the more regular the orientation of the side groups, the closer the packing, and the stronger the polymer 
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Elastomers and fibres


  • soft and springy
  • can be stretched, but they return their original shape


  • can be made into strong, thing threads
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  • No cross-links between the chains
  • Intermolecular bonds between the chains are much weaker than the covalent cross-links in a thermoset
  • Attractive forces can be overcome by heating
  • The chains can slide over one another and the polymer can be deformed
  • After being deformed, on cooling, the weak bonds between the chains reform and the thermoplastic holds its new shape
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  • Extensive cross-linking between the polymer chains
  • Bonds between the chains are much stronger than in thermoplastics
  • The covalent bonds cannot be broken by heating
  • Chains are unable to move relative to each other and the polymer cannot change shape
  • If a thermoset is heated for an extensive period, the polymer chars and burns
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