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20 Polymerisation

20.1 Addition polymerisation

Addition Polymerisation

Specification Reference Organic Chemistry, Polymerisation 20.1

Quick Notes

  • Addition polymers are made by joining many alkene monomers through addition reactions.
  • Polymers are made up of repeating units (the smallest unit of a polymer that is bonded in a repeating pattern).
  • Common examples include poly(ethene) and poly(chloroethene) (PVC).
  • Polyalkenes are unreactive and not biodegradable – they persist in the environment.
  • Combustion of polymers like PVC can release toxic gases (e.g. HCl).

Full Notes

What Is Addition Polymerisation?

Addition polymers are (very) large molecules made up of repeating units, bonded together over and over again. Repeating units are formed from small molecules called monomers.

Addition polymers are formed by joining many alkene monomers in an addition reaction.

Monomers must contain a C=C double bond.

Example Ethene (CH2=CH2) → Poly(ethene)

CIE A-Level Chemistry diagram showing addition polymerisation of ethene into poly(ethene) through repeating units.

Deducing the Repeat Unit from a Monomer

An addition polymer’s repeating unit is based on the monomer structure.

How to draw a repeating unit from a monomer:

CIE A-Level Chemistry example of poly(chloroethene) (PVC) polymerisation from vinyl chloride monomers, showing repeating unit formation.
  1. Redraw the monomer with the C=C double bond in the middle of the structure.
  2. Break the C=C double bond.
  3. Extend single bonds from the two carbons to show the continuation of the polymer chain.

Identifying the Monomer from a Polymer

To find the monomer from a polymer chain:

CIE A-Level Chemistry diagram showing how to identify monomers from polymers by restoring C=C bonds from the repeating unit.
  1. Identify the repeating unit.
  2. Restore the C=C double bond.

Properties of Addition Polymers

Addition polymers are chemically inert because strong C–C and C–H bonds make addition polymers very unreactive.

They are also Non-biodegradable: These materials are not broken down naturally, causing long-term environmental issues. The strength and stability of the carbon chain makes these materials resistant to biological and chemical degradation.

Environmental Issues

The use of addition polymers can cause environmental issues.

As a result, care must be taken when disposing of polymers, particularly halogenated ones like PVC, due to the risk of toxic emissions.

Summary