Polymerisation

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Polymerisation

• Addition Polymerisation
• Condensation Polymerisation
• Uses of polymers

2
Addition Polymerisation

• A carbon carbon double bond is needed in the
  monomer
• A monomer is the small molecule that makes up the
  polymer

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Addition Polymerisation

• The polymer is the only product
• Involves the opening out of a double bond
• The conditions of the reaction can alter the
  properties of the polymer
• Reaction proceeds by a free radical mechanism
• Oxygen often used as the initiator

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Addition polymerisation

• The board specifies that you know this addition
  polymerisation reaction

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Addition polymerisation

• Conditions are high pressure and an oxygen
  initiator (to provide the initial free radical).
• Monomer phenylethene
• Polymer poly(phenylethene)

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Addition Polymerisation

• You are expected to be able to do the following
  things with addition polymers
• Predict the repeating unit of the polymer given
  the monomer
• Predict the monomer from the polymer displayed
  formula and even empirical formula.
• Know about stereochemistry of addition polymers.

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Prediction the repeating unit

• This is easy, basically open out the double bond.
  

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Predicting the monomer from the polymer

• This is kind of the opposite to what you have
  just done.
• They may ask you to draw different formulae.
• You need to make sure you can convert repeating
  units into monomers, and draw a ring around the
  repeating unit

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Stereoisomerism in Addition polymers.

• Ziegla and Natta in the 1950s cam up with a way
  of controlling the repeating unit.
• They won a Joint Nobel prize for their work
• The polymerisation process can be controlled used
  a tin/aluminium catalyst at 50C and 1.5atm

10
Stereoisomerism in Addition polymers.

• Previous to this only one type of poly(ethene)
  could be made, called LDPE or low density
  poly(ethane).
• The chains formed a tangled mass.
• HDPE could now be produced.
• This has a much stiffer structure due to areas of
  crytallinity where the polymer chains are much
  more ordered.

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Stereoisomerism in Addition polymers.

• HDPE has a much higher boiling point due to these
  more ordered regions.
• Generally used to make plastic bottles.
• Ziegler and Natta also discovered that they could
  make stereo regular polymers. Isotactic,
  syndiotactic and atactic.

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Poly(propene) and stereoisomerism

• Isotactic. This is a very regular type of polymer
  chain. All the methyl groups are on the same
  side.

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Poly(propene) and stereoisomerism

• Syndiotactic. A slightly less regular but still
  very ordered polymer.
• The methyl groups alternate the side of chain
  they are on.

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Poly(propene) and stereoisomerism

• Atactic.
• This is a completely random allocation of methyl
  groups along the carbon skeleton.

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Poly(propene) and stereoisomerism

• This varying degree of randomness will affect the
  strength and melting point of the polymer.
• The less random, the stronger the polymer and the
  higher the melting point
• This is because in a more ordered polymer they
  chains can get closer together and hence the van
  der Waals forces will be greater.

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Condensation Polymers

• Involves 2 monomers that have different
  functional groups.
• They also involve the elimination of water or
  another small molecule.
• Hence the term condensation polymer.
• Monomer A Monomer B ? Polymer small molecule
  (normally water).
• Common condensation polymers include polyesters
  (the ester linkage) and polyamides (the amide
  linkage as in proteins).

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Polyesters

• The OCR example here is terylene, a polymer of
  benzene-1,4-dicarboxylic acid and
  ethane-1,2-diol.
• The ester linkage is formed between the monomers

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Polyesters

• You need to be able to reproduce the formation of
  terylene, and possibly predict the structures of
  other polyesters

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Polyamides

• These involve the linkage of two monomers through
  the amide linkage as in proteins (e.g. silk)

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Nylon 6,6 a polyamide
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Kevlar a polyamide
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Uses of polyamides

• The main use of polyesters and polyamides is as
  fibres in clothing.
• Most clothing now has a degree of manufactured
  fibres woven into the natural material (such as
  cotton).
• This gives the material more desirable
  characteristics, such as stretchiness, and better
  washability.
• Dont forget that proteins are also polyamides,
  you must know how the linkage works with natural
  polymers such as proteins.