Polymers: Natural and Synthetic
Natural and synthetic polymers in IGCSE Chemistry: addition and condensation polymerisation, examples, uses, environmental impact, and disposal for Cambridge 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Polymers are tested across multiple parts of the Cambridge 0620 syllabus — organic chemistry, environmental chemistry, and the properties of materials. Questions range from drawing repeat units to discussing the environmental impact of plastic waste.
What is a polymer?
A polymer is a very large molecule made by joining together many small molecules called monomers. The process of forming a polymer is called polymerisation.
- Poly = many
- Mer = unit
- The polymer chain may contain thousands or millions of repeating units
Addition polymerisation
Requirements
- Monomers must be unsaturated — they contain a C=C double bond (alkenes)
- No other product is formed — the polymer is the only product
Mechanism
The C=C double bond in each monomer “opens up,” and the monomers link together to form a long chain with only C-C single bonds.
n C₂H₄ → (–CH₂–CH₂–)ₙ
Common addition polymers
| Monomer | Polymer | Uses |
|---|---|---|
| Ethene (C₂H₄) | Poly(ethene) / polyethylene | Plastic bags, bottles, packaging |
| Propene (C₃H₆) | Poly(propene) / polypropylene | Ropes, crates, car parts |
| Chloroethene (C₂H₃Cl) | Poly(chloroethene) / PVC | Pipes, window frames, insulation |
| Tetrafluoroethene (C₂F₄) | PTFE (Teflon) | Non-stick pans, waterproof coatings |
Drawing the repeat unit
To draw the repeat unit from the monomer:
- Open the C=C double bond to C-C single bond
- Show continuation bonds extending from each carbon
- Place brackets around the unit with subscript n
To identify the monomer from a polymer repeat unit:
- Take the section inside the brackets
- Replace the single C-C bond with a C=C double bond
- Remove the continuation bonds
Condensation polymerisation (Supplement)
Requirements
- Monomers have two functional groups (one at each end)
- A small molecule (usually water, H₂O) is eliminated with each link formed
Examples
Nylon: made from a diamine and a dicarboxylic acid. An amide link (–CONH–) forms between each pair, releasing H₂O.
Polyester (e.g. Terylene): made from a diol and a dicarboxylic acid. An ester link (–COO–) forms between each pair, releasing H₂O.
| Feature | Addition polymerisation | Condensation polymerisation |
|---|---|---|
| Monomers | One type (alkene) | Usually two types |
| Functional groups needed | C=C double bond | Two functional groups per monomer |
| Small molecule produced? | No | Yes (H₂O) |
| Link type | C-C bonds only | Amide or ester |
Natural polymers
Not all polymers are synthetic. Nature produces several important polymers:
| Natural polymer | Monomer | Found in |
|---|---|---|
| Starch | Glucose | Plants (rice, potatoes) |
| Cellulose | Glucose | Plant cell walls (cotton, paper) |
| Proteins | Amino acids | Muscles, enzymes, hair |
| DNA | Nucleotides | Cell nuclei |
| Natural rubber | Isoprene | Rubber trees (Malaysia is a major producer) |
Natural rubber is particularly significant in Malaysia — the country is one of the world’s largest rubber producers. The rubber tree (Hevea brasiliensis) produces latex, which is processed into natural rubber (poly(isoprene)).
Proteins and starch are condensation polymers — water is released when amino acids or glucose units link together.
Environmental impact of polymers
The problem
- Most synthetic polymers are non-biodegradable — microorganisms cannot break them down
- Plastic waste accumulates in landfill and oceans
- Marine animals mistake plastic for food
- Plastic takes hundreds of years to degrade
Solutions
| Approach | How it works | Limitation |
|---|---|---|
| Recycling | Melt and reshape thermoplastics | Not all plastics are recyclable; sorting is needed |
| Incineration | Burn plastics for energy | Produces CO₂ and may release toxic gases (HCl from PVC) |
| Biodegradable polymers | Polymers designed to be broken down by bacteria | More expensive to produce |
| Reduce and reuse | Use less plastic; reuse bags and containers | Requires behaviour change |
Worked exam question
Ethene can be polymerised to form poly(ethene). (a) What type of polymerisation is this? [1] (b) Draw the repeat unit of poly(ethene). [1] (c) State one environmental problem caused by poly(ethene). [1]
(a) Addition polymerisation [1]
(b) (–CH₂–CH₂–)ₙ showing the repeat unit with continuation bonds and brackets [1]
(c) Poly(ethene) is non-biodegradable, so it persists in landfill/the environment for a very long time and can harm wildlife [1]
Common exam mistakes
- Saying addition polymers release water — addition polymerisation produces no by-product. Only condensation polymerisation releases water.
- Drawing the repeat unit with a double bond — the C=C bond opens up during polymerisation, so the repeat unit has only single bonds.
- Forgetting the n subscript and continuation bonds when drawing a repeat unit.
- Saying “plastic is biodegradable” — most synthetic polymers are not biodegradable, which is precisely the environmental problem.
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