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This lesson covers addition polymers and condensation polymers as required by the AQA GCSE Chemistry specification (5.8.2). Polymers are large molecules made by joining many small molecules together. Understanding how polymers are formed and their properties is essential for GCSE Chemistry. Condensation polymerisation is Higher Tier only [H].
A polymer is a very large molecule (a macromolecule) made by joining together many small molecules called monomers. The process of joining monomers together is called polymerisation.
| Term | Definition |
|---|---|
| Monomer | A small molecule that can join with many others to form a polymer |
| Polymer | A very large molecule made up of many repeating monomer units |
| Polymerisation | The chemical reaction in which monomers join together to form a polymer |
There are two types of polymerisation:
| Type | Monomer Requirement | By-product | Level |
|---|---|---|---|
| Addition polymerisation | Alkenes (contain C=C double bond) | None | Foundation and Higher |
| Condensation polymerisation | Monomers with two functional groups | Small molecule (e.g., water) | Higher only [H] |
Exam Tip: Know the difference between the two types of polymerisation. Addition polymerisation produces only the polymer (no by-product). Condensation polymerisation produces the polymer AND a small molecule (usually water).
Addition polymerisation occurs when many alkene monomers join together. The C=C double bond in each monomer breaks open, and the monomers link together in a long chain through single C–C bonds.
Key features:
| Monomer | Polymer | Uses |
|---|---|---|
| Ethene (C2H4) | Poly(ethene) — commonly called polythene | Plastic bags, bottles, packaging, cling film |
| Propene (C3H6) | Poly(propene) — commonly called polypropylene | Ropes, carpet fibres, food containers, car bumpers |
| Chloroethene (C2H3Cl) | Poly(chloroethene) — commonly called PVC | Window frames, pipes, electrical cable insulation, flooring |
| Tetrafluoroethene (C2F4) | Poly(tetrafluoroethene) — PTFE (Teflon) | Non-stick coatings, waterproof fabrics (Gore-Tex) |
| Styrene (C8H8) | Polystyrene | Packaging, insulation, disposable cups |
graph LR
A["Many Alkene Monomers<br/>(e.g. Ethene C2H4)"] -->|"Addition Polymerisation"| B["Addition Polymer<br/>(e.g. Poly(ethene))"]
C["C=C double bonds break"] --> D["New C-C single bonds form"]
D --> E["Long polymer chain"]
F["No by-product<br/>No atoms lost"]
style A fill:#27ae60,color:#fff
style B fill:#2980b9,color:#fff
The repeat unit is the smallest section of the polymer chain that, when repeated, gives the full polymer. For addition polymers:
Exam Tip: You must be able to draw the repeat unit of an addition polymer from the monomer, and identify the monomer from the repeat unit. Remember: the repeat unit has single bonds (the double bond has opened), and extension bonds come out of both sides of the brackets.
Condensation polymerisation occurs when monomers with two functional groups join together. Each time two monomers link, a small molecule (usually water) is released as a by-product. This is what distinguishes it from addition polymerisation.
Key features:
Formed by the condensation reaction between:
The linkage formed is an ester link (–COO–), and a molecule of water (H2O) is released each time a link forms.
| Component | Functional Groups | Role |
|---|---|---|
| Dicarboxylic acid | –COOH at both ends | Provides one half of the ester link |
| Diol | –OH at both ends | Provides the other half of the ester link |
Example: PET (polyethylene terephthalate) is a common polyester used in plastic bottles and polyester clothing.
Formed by the condensation reaction between:
The linkage formed is an amide link (–CONH–), also called a peptide link in biological contexts. A molecule of water is released each time a link forms.
| Component | Functional Groups | Role |
|---|---|---|
| Dicarboxylic acid | –COOH at both ends | Provides one half of the amide link |
| Diamine | –NH2 at both ends | Provides the other half of the amide link |
Example: Nylon is a polyamide used in clothing, ropes, carpets, and engineering plastics.
Exam Tip: [H] For condensation polymerisation, remember: TWO different types of monomer react together, each with TWO functional groups, and a small molecule (usually water) is lost. For polyesters the link is –COO–; for polyamides the link is –CONH–.
| Feature | Addition Polymerisation | Condensation Polymerisation [H] |
|---|---|---|
| Monomer type | Alkenes (with C=C double bond) | Monomers with two functional groups |
| Number of monomer types | One type | Usually two types |
| By-product | None | Small molecule (usually water) |
| Link type | C–C single bonds | Ester links (–COO–) or amide links (–CONH–) |
| Examples | Poly(ethene), PVC, polystyrene | Polyester (PET), nylon (polyamide) |
Different polymers have different properties, making them suitable for different applications:
| Polymer | Key Properties | Uses |
|---|---|---|
| Poly(ethene) | Flexible, waterproof, cheap, lightweight | Plastic bags, bottles, packaging |
| Poly(propene) | Strong, flexible, heat-resistant | Food containers, ropes, carpets |
| PVC | Rigid or flexible, durable, electrical insulator | Pipes, window frames, cable insulation |
| PTFE (Teflon) | Very low friction, heat-resistant, non-reactive | Non-stick coatings, waterproof clothing |
| Polystyrene | Lightweight, good thermal insulator (when expanded) | Packaging, insulation, disposable cups |
| Polyester (PET) [H] | Strong, lightweight, can be drawn into fibres | Plastic bottles, clothing fibres |
| Nylon (polyamide) [H] | Very strong, tough, can be drawn into fibres | Clothing, ropes, carpets, gears |
Most polymers are non-biodegradable — they are not broken down by microorganisms. This creates significant environmental problems:
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