4.8 Synthetic Polymers

REVISION NOTES

IGCSE Edexcel Chemistry

4.8.1 Know that an addition polymer is formed by joining up many small molecules called monomers

ADDITION POLYMERS

Addition polymer is formed when many small molecules join together
The process is called addition polymerisation
The small molecules are called monomers (like lego building blocks)

4.8.2 Understand how to draw the repeat unit of an addition polymer, including poly(ethene), poly(propene), poly(chloroethene) and (poly)tetrafluoroethene

FORMATION OF POLYMERS

Polymers are formed by joining many monomers with C=C bonds together
One of the bonds in each C=C bonds breaks and forms a bond with the adjacent monomer (like holding hands together)
Monomers can be a variety of compounds with C=C bonds
- E.g. ethene, propene, chloroethene and tetrafluoroethene

NAMING POLYMERS

Prefix: poly–
+ name of the monomer
E.g. propene → poly(propene)

4.8.3 Understand how to deduce the structure of a monomer from the repeat unit of an addition polymer and vice versa

DEDUCING POLYMER REPEAT UNIT FROM MONOMER

Draw several monomers next to each other
Remove one of the bonds in C=C
New bonds are formed in between the monomers, connecting monomers together

DEDUCING MONOMER FROM POLYMER UNIT

Find the repeating unit in the polymer
Draw only one repeating unit
Remove the connecting bonds
Add a second bond between C and C to form C=C bond

4.8.4 Explain problems in the disposal of addition polymers, including:

Their inertness and inability to biodegrade
The production of toxic gases when they are burned.

PROBLEMS IN DISPOSAL OF ADDITION POLYMERS

1. Landfill

Addition polymers are formed by joining many monomers together with strong C-C bonds
As a result, addition polymers are unreactive and chemically inert
Polymers do not easily biodegrade

2. Incineration

If polymers are burned, toxic gases may be produced
Complete combustion: carbon dioxide (greenhouse gas)
Incomplete combustion: carbon monoxide (toxic gas that reduces the capacity of blood to carry oxygen)
Burning polymers with chlorine (e.g. PVC): hydrogen chloride gas (toxic gas)

4.8.5C Know that condensation polymerisation, in which a dicarboxylic acid reacts with a diol, produces a polyester and water

CONDENSATION POLYMERS

Recall: alcohol + carboxylic acid → ester + H₂O
Dicarboxylic acid: functional group -COOH is present on both ends of the compound
Diol: functional group -OH is present on both ends of the compound
Condensation (esterification) can occur on both ends of alcohol and carboxylic acid compounds, forming a long polymer

4.8.6C Understand how to write the structural and displayed formula of a polyester, showing the repeat unit, given the formulae of the monomers from which it is formed including the reaction of ethanedioic acid and ethanediol: