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Polymerisation

Polymerisation. Addition Polymerisation Condensation Polymerisation Uses of polymers. Addition Polymerisation. A carbon – carbon double bond is needed in the monomer A monomer is the small molecule that makes up the polymer. Addition Polymerisation. The polymer is the only product

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Polymerisation

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  1. 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

  3. 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

  4. Addition polymerisation • The board specifies that you know this addition polymerisation reaction

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

  6. 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.

  7. Prediction the repeating unit • This is easy, basically open out the double bond.

  8. 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

  9. 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 50°C 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.

  11. 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.

  12. Poly(propene) and stereoisomerism • Isotactic. This is a very regular type of polymer chain. All the methyl groups are on the same side.

  13. 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.

  14. Poly(propene) and stereoisomerism • Atactic. • This is a completely random allocation of methyl groups along the carbon skeleton.

  15. 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 Waal’s forces will be greater.

  16. 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).

  17. 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

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

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

  20. Nylon 6,6 a polyamide

  21. Kevlar a polyamide

  22. 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. • Don’t forget that proteins are also polyamides, you must know how the linkage works with natural polymers such as proteins.

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