Addition polymerisation — AQA GCSE Chemistry
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Addition polymerisation explained
Addition polymerisation covers 4 specification points, including Alkenes can be used to make polymers such as… and In addition polymerisation reactions, many….
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Open a point below for its explanation and revision guidance.
Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation.
Addition polymerisation is the process in which many small unsaturated alkene molecules, called monomers, join together to form a large saturated molecule called a polymer. The monomers contain a carbon-carbon double bond, which opens up during the reaction. For example, ethene monomers join to form poly(ethene), and propene monomers join to form poly(propene). The polymer is the only product, so no other small molecule is eliminated. You should be able to recognise the repeat unit in a polymer structure, draw the repeat unit from a given monomer, and identify the monomer from a given polymer. The general equation can be represented as n monomer → polymer, where n is a large number. The double bond becomes a single bond in the polymer chain.
In addition polymerisation reactions, many small molecules (monomers) join together to form very large molecules (polymers).
Addition polymerisation is a type of reaction in which many small unsaturated molecules, called monomers, join together to form one very large saturated molecule, called a polymer. The monomers must contain a carbon–carbon double bond, C=C. During the reaction, this double bond opens up and each monomer forms new single bonds to two neighbouring monomers, creating a long chain. For example, ethene, CH₂=CH₂, polymerises to form poly(ethene), a long chain of –CH₂–CH₂– units. No other product is formed, so all the atoms of the monomers end up in the polymer. The reaction is represented by showing the monomer and the repeating unit, with the double bond replaced by single bonds and the chain extended by bonds to other repeating units.
For example: In addition polymers the repeating unit has the same atoms as the monomer because no other molecule is formed in the reaction.
In addition polymerisation, the repeating unit of the polymer contains exactly the same atoms as the monomer. This is because no small molecule is eliminated during the reaction; all the atoms of each monomer become part of the polymer chain. For example, the monomer ethene, CH₂=CH₂, has two carbon atoms and four hydrogen atoms. Its polymer, poly(ethene), has a repeating unit –CH₂–CH₂– that also contains two carbon atoms and four hydrogen atoms. The only change is that the C=C double bond becomes a C–C single bond, and each carbon forms bonds to neighbouring repeating units. When drawing the repeating unit, show the two carbon atoms with single bonds and place the bonds that connect to the rest of the chain outside the brackets.
Students should be able to: recognise addition polymers and monomers from diagrams in the forms shown and from the presence of the functional group C=C in the monomers draw diagrams to represent the formation of a polymer from a given alkene monomer relate the repeating unit to the monomer. AQA GCSE Chemistry 8462. GCSE exams Jun
Students need to recognise addition polymers and their monomers from diagrams. Monomers are alkenes and contain the C=C functional group; polymers are long-chain saturated molecules made of repeating units. When drawing the formation of a polymer from a given alkene monomer, show the monomer with its C=C double bond, then show the repeating unit with single bonds and extension bonds. The repeating unit must have the same atoms as the monomer. For example, propene, CH₂=CHCH₃, forms poly(propene) with the repeating unit –CH₂–CH(CH₃)–. To relate the repeating unit to the monomer, identify the two carbon atoms that were part of the double bond and note that they now form single bonds to neighbouring units. Practise converting between monomer and repeating unit diagrams accurately.
Your focus
- Describe addition polymerisation as the joining of unsaturated monomers to form a polymer.
- Draw the repeat unit of poly(ethene) and poly(propene) from their monomers.
- Identify the monomer from a given addition polymer structure.
Show all 12 objectives
- Define addition polymerisation as the joining of many small unsaturated monomers to form a large saturated polymer.
- Identify the C=C double bond as the functional group required for addition polymerisation.
- Represent the formation of a polymer from a given monomer by showing the opening of the double bond and the repeating unit.
- Draw the repeating unit of an addition polymer from a given monomer.
- Explain why the repeating unit contains the same atoms as the monomer.
- Relate the structure of the repeating unit to the monomer by identifying the change from a double to a single bond.
- Recognise addition polymers and monomers from diagrams and from the presence of C=C.
- Draw diagrams to represent the formation of a polymer from a given alkene monomer.
- Relate the repeating unit of a polymer to its monomer.
Addition polymerisation exam tips
Marking Points
- Define addition polymerisation as the joining of many unsaturated monomer molecules to form a polymer.
- Identify ethene and propene as monomers used to make poly(ethene) and poly(propene).
- Recognise the carbon-carbon double bond in an alkene monomer and explain that it opens during polymerisation.
- Draw or identify the repeat unit of a polymer from a given monomer structure.
- Identify the monomer from a given polymer structure by locating the two-carbon repeat unit and restoring the double bond.
- Addition polymerisation involves many small monomer molecules joining together.
- The monomers are unsaturated and contain a C=C double bond.
- The product is a very large molecule called a polymer.
- The reaction opens the C=C double bond, allowing each monomer to bond to two others.
- No other molecule is formed; all atoms of the monomers become part of the polymer chain.
- The polymer is a saturated long-chain molecule made of repeating units derived from the monomer.
- The repeating unit of an addition polymer has the same atoms as the monomer.
- No other molecule is formed during addition polymerisation, so no atoms are lost.
- The double bond in the monomer becomes a single bond in the repeating unit.
- The repeating unit is shown with bonds extending from the carbon atoms to indicate continuation of the chain.
- For ethene, the repeating unit is –CH₂–CH₂–, which contains the same atoms as CH₂=CH₂.
- Recognise the C=C double bond as the functional group present in monomers for addition polymerisation.
- Identify addition polymers from diagrams showing a saturated carbon chain with repeating units.
- Draw the formation of a polymer from a given alkene by opening the double bond and joining monomers.
- Draw the repeating unit of a polymer from a given monomer, ensuring the same atoms are present.
- Relate the repeating unit to the monomer by identifying the carbon atoms that were double-bonded and now form single bonds.
- Use correct notation for repeating units, including brackets and extension bonds.
Examiner Tips
- 💡When drawing a repeat unit, show the two carbon atoms of the original double bond with single bonds and extend the bonds through the brackets.
- 💡Check that the polymer repeat unit has the same atoms as the monomer, with no atoms added or removed.
- 💡Use the name of the monomer to derive the polymer name, for example ethene gives poly(ethene).
- 💡When describing addition polymerisation, always mention the C=C double bond in the monomer and that it becomes single bonds in the polymer.
- 💡Use the term 'repeating unit' when explaining the structure of the polymer, and show it with bonds extending beyond the brackets.
- 💡Check that your answer states that no other product is formed, as this distinguishes addition from condensation polymerisation.
- 💡When drawing a repeating unit, always place the extension bonds through the brackets to show that the unit repeats.
- 💡Count the atoms in the monomer and in your repeating unit to check they are identical.
- 💡Remember that addition polymers are named by adding 'poly' before the monomer name, for example poly(ethene).
- 💡When given a diagram of a polymer, work backwards to identify the monomer by finding the repeating unit and restoring the C=C double bond.
- 💡Always check that the number of each type of atom in the repeating unit matches the monomer.
- 💡Practise drawing repeating units for common monomers such as ethene, propene and chloroethene.
Common Mistakes
- Drawing the repeat unit with a double bond still present; correct by showing a single bond between the carbon atoms in the polymer backbone.
- Omitting the 'n' or placing it inside the brackets; correct this by placing the repeat unit in brackets with a subscript 'n' outside to show many units join.
- Confusing addition polymerisation with condensation polymerisation; correct by noting that addition polymerisation produces only the polymer, whereas condensation polymerisation produces a small molecule such as water as well.
- Thinking that addition polymerisation produces a small molecule such as water; correct this by stating that no other molecule is formed.
- Believing that any small molecule can undergo addition polymerisation; correct this by specifying that the monomer must contain a C=C double bond.
- Writing the polymer as a collection of separate monomer molecules rather than one long chain; correct this by showing the repeating unit joined by single bonds.
- Drawing the repeating unit with a double bond; correct this by showing only single bonds between carbon atoms.
- Omitting the bonds that connect the repeating unit to the rest of the polymer chain; correct this by adding single bonds extending outside the brackets.
- Including extra atoms such as H₂O in the repeating unit; correct this by using only the atoms present in the monomer.
- Confusing addition and condensation polymers; correct this by checking that the monomer contains C=C and that no small molecule is eliminated.
- Drawing the repeating unit with the double bond still present; correct this by showing only single bonds between carbon atoms.
- Forgetting to include side groups such as CH₃ in the repeating unit; correct this by copying all atoms from the monomer into the repeating unit.