Making polymers

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Whats a polymer?

A large molecule formed when many smaller molecules bond together

Under high pressure and in the presence of a catalyst many monomer molecules join together to make polymer molecules.

These polymer molecules are saturated.

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Hydrocarbons, alkanes and alkenes

Hydrocarbon - compounds made from only hydrogen and carbon atoms, joined by covalent bonds

Alkanes - saturated, only have a single bond

Alkenes - unsaturated, have double bonds - alkenes can also act as monomers

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Testing for alkenes

Only alkenes will react and decolourise bromine water

Bromine water is an orange solution of bromine. It becomes colourless when shaken with an alkene. Alkenes can decolourise bromine water, while alkanes cannot

The reaction between bromine and alkenes is an example of a type of reaction called an addition reaction

The bromine is decolourised because a colourless dibromo compound forms

ethene + bromine → dibromoethane

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Alkenes

Alkenes are hydrocarbons that contain a carbon-carbon double bond

The number of hydrogen atoms in an alkene is double the number of carbon atoms

Alkenes are able to act as monomers because they contain a double bond

The presence of this double bond allows alkenes to react in ways that alkanes cannot

They are UNSATURATED

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Alkanes

Alkanes are SATURATED

Alkanes are a type of hydrocarbon

The number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two

Alkanes are saturated hydrocarbons which means their carbon atoms are joined to each other by single covalent bonds

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Polymerisation

  • change the double bond in the monomer to a single bond in the repeating unit
  • add a bond to each end of the repeating unit

Monomer is unsaturated, but the polymer is saturated

An ethene monomer has four hydrogen atoms and two carbon atoms that are joined together with a double bond. After polymerisation, the monomer forms a repeating unit of polyethene which has single bonds between the carbon atoms. A chloroethene monomer has three hydrogen atoms, one chlorine atom and two carbon atoms. The carbon atoms are joined together with a double bond. After polymerisation, the monomer forms a repeating unit of polychloroethene that has single bonds between the carbon atoms (http://www.bbc.co.uk/staticarchive/27d0683fa70c3e16981827d9a27c974f82625525.gif)

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