Polymers
Summary: Addition polymers form when monomers with C=C bonds join without byproducts (poly(ethene), poly(propene), PVC, PTFE). Condensation polymers form with elimination of a small molecule (nylon, terylene). Natural polymers include proteins, starch, and cellulose. Polymers cause pollution problems due to non-biodegradability. Tags: igcse chemistry organic-chem Created: 2026-07-14 Last Updated: 2026-07-16
Learning Objectives
By the end of this topic, you should be able to:
- Describe addition polymerisation and give examples (poly(ethene), poly(propene), PVC, PTFE)
- Draw the repeating unit of an addition polymer from its monomer and vice versa
- Describe condensation polymerisation (nylon, terylene) if in syllabus
- Identify natural polymers (proteins, starch, cellulose) and their monomer units
- State properties and uses of common polymers
- Discuss the pollution problems caused by polymers (non-biodegradable, landfill, incineration)
Content
1. What is a Polymer?
A polymer is a long-chain molecule made from many small repeating units called monomers. The process of joining monomers together is called polymerisation.
Two main types:
- Addition polymerisation: Monomers with C=C double bonds join together; no other product is formed
- Condensation polymerisation: Monomers join with the elimination of a small molecule (usually water)
2. Addition Polymerisation
The General Process
Addition polymers form from alkene monomers (molecules containing C=C). The double bond opens up, and monomers link together to form a long saturated carbon chain.
General equation for ethene:
n CH2=CH2 → -(CH2-CH2)-n
- The monomer is the alkene
- The repeating unit is the part inside the brackets
nis a large number (degree of polymerisation)
Key Addition Polymers to Know
| Monomer | Polymer | Repeating Unit | Properties | Uses |
|---|---|---|---|---|
| Ethene (CH2=CH2) | Poly(ethene) / Polythene | -(CH2-CH2)- | Flexible, waterproof, electrical insulator | Plastic bags, bottles, cling film, buckets |
| Propene (CH2=CHCH3) | Poly(propene) / Polypropylene | -(CH2-CHCH3)- | Tough, higher melting point than poly(ethene) | Ropes, carpets, crates, car bumpers, syringes |
| Chloroethene (CH2=CHCl) | PVC (Polyvinyl chloride) | -(CH2-CHCl)- | Rigid (unplasticised) or flexible (plasticised), waterproof | Window frames, drainpipes, electrical insulation, flooring |
| Tetrafluoroethene (CF2=CF2) | PTFE (Polytetrafluoroethene / Teflon) | -(CF2-CF2)- | Non-stick, heat-resistant, very low friction | Non-stick pans, bearings, waterproof clothing, lab equipment |
How to Draw the Repeating Unit from a Monomer
Rule: Take the alkene monomer, “open” the double bond, and draw it with extended bonds on each side (crossing the brackets).
Example 1: Monomer = CH2=CH2 (ethene) → Repeating unit = -(CH2-CH2)-
Example 2: Monomer = CH2=CHCl (chloroethene) → Repeating unit = -(CH2-CHCl)-
Example 3: Monomer = CH2=CHCH3 (propene) → Repeating unit = -(CH2-CHCH3)-
Exam tip: Always show the bonds extending through the brackets on both sides: -[repeating unit]-. This shows that the chain continues in both directions. The side group (Cl, CH3, F etc.) must be shown clearly.
How to Identify the Monomer from a Repeating Unit
Rule: Take the repeating unit and convert it back to the alkene by forming the C=C double bond.
Example: Repeating unit = -(CH2-CF2)- → Monomer = CF2=CF2 (tetrafluoroethene)
Example: Repeating unit = -(CH2-CHCH3)- → Monomer = CH2=CHCH3 (propene)
3. Condensation Polymerisation (Extension)
Condensation polymers form when two different monomers join, eliminating a small molecule (usually water) each time. Two important examples:
Terylene (Polyester)
- Monomers: A diol (ethane-1,2-diol / HOCH2CH2OH) + a dicarboxylic acid (benzene-1,4-dicarboxylic acid / HOOC-C6H4-COOH)
- Linkage formed: Ester linkage (-COO-)
- Small molecule eliminated: Water (H2O)
- This is why it is called a polyester
- Uses: Clothing fibres (terylene/cotton blends), sails, conveyor belts
Nylon (Polyamide)
- Monomers: A diamine (H2N-(CH2)6-NH2) + a dicarboxylic acid (HOOC-(CH2)4-COOH)
- Linkage formed: Amide linkage (-CONH-)
- Small molecule eliminated: Water (H2O)
- This is why it is called a polyamide
- Uses: Ropes, stockings, parachutes, fishing line
4. Natural Polymers
| Natural Polymer | Monomer(s) | Type of Linkage | Function |
|---|---|---|---|
| Proteins | Amino acids (20 different types) | Peptide bonds (-CONH-) | Enzymes, structure (muscle, hair, skin), transport, hormones |
| Starch | Glucose (alpha-glucose) | Glycosidic bonds | Energy storage in plants |
| Cellulose | Glucose (beta-glucose) | Glycosidic bonds | Structural — cell walls in plants |
| DNA | Nucleotides | Phosphodiester bonds | Genetic information storage |
Proteins are natural condensation polymers/polyamides. Amino acids link via peptide bonds, eliminating water.
Starch vs Cellulose: Both made from glucose monomers, but different linkages (alpha vs beta) give them very different properties — starch is digestible by humans; cellulose is not.
5. Properties and Uses Summary Table
| Polymer | Key Property | Why It’s Used For… |
|---|---|---|
| Poly(ethene) | Flexible, waterproof, cheap | Plastic bags, bottles, packaging film |
| Poly(propene) | Tough, higher mp, chemical resistance | Ropes, crates, medical syringes, car parts |
| PVC | Strong, can be rigid or flexible | Pipes, window frames, electrical insulation |
| PTFE | Non-stick, heat resistant, inert | Non-stick pans, bearings, chemical equipment |
| Nylon | Strong, elastic, lightweight | Ropes, clothing, parachutes, fishing line |
| Terylene | Crease-resistant, strong | Clothing, sails, conveyor belts |
6. Pollution Problems with Polymers
Polymers (plastics) cause significant environmental problems:
| Problem | Detail |
|---|---|
| Non-biodegradable | Most addition polymers (poly(ethene), PVC, etc.) do not rot or decompose naturally. They persist in the environment for hundreds of years |
| Landfill | Discarded plastics fill landfill sites. They are bulky and do not break down, taking up space indefinitely |
| Incineration (burning) | Burning plastics can release toxic gases: PVC produces HCl (hydrogen chloride) gas; incomplete combustion produces CO (carbon monoxide) and particulates |
| Marine pollution | Plastic waste in oceans harms wildlife — animals become entangled or ingest plastics (e.g., plastic bags mistaken for jellyfish by turtles) |
| Microplastics | Larger plastics break into tiny fragments that enter food chains |
Solutions / Mitigations
- Recycling: Melting and remoulding thermoplastic polymers (poly(ethene), poly(propene), PVC). Recycling codes (1-7) identify the polymer type
- Biodegradable polymers: Made from plant starch (e.g., PLA — polylactic acid) — these can be broken down by microorganisms
- Incineration with energy recovery: Burning plastics to generate electricity (but produces CO2 and possibly toxic gases)
- Reducing use: Reusable bags, bottles, and containers
Recycling Codes
| Code | Polymer | Common Products |
|---|---|---|
| 1 PET(E) | Polyethylene terephthalate | Drink bottles |
| 2 HDPE | High-density poly(ethene) | Milk jugs, detergent bottles |
| 3 PVC | Polyvinyl chloride | Pipes, window frames |
| 4 LDPE | Low-density poly(ethene) | Plastic bags, squeeze bottles |
| 5 PP | Poly(propene) | Yogurt tubs, bottle caps |
| 6 PS | Polystyrene | Foam cups, packaging |
Worked Examples (Exam-Style)
Example 1: Drawing Repeating Units
Question: Draw the repeating unit of poly(propene). [2 marks]
Solution: The monomer is propene: CH2=CHCH3 Opening the double bond:
H H
| |
-(-C - C -)-
| |
H CH3
Shorthand: -(CH2-CHCH3)- ✓
Example 2: Identifying the Monomer
Question: The repeating unit of a polymer is -(CH2-CCl2)-. Name the monomer. [1 mark]
Solution: Convert repeating unit back to alkene: CH2=CCl2 Name: 1,1-dichloroethene ✓
Example 3: Pollution Problems
Question: Explain two problems caused by the disposal of plastics. [4 marks]
Solution (model answer):
- Plastics are non-biodegradable / do not decompose naturally ✓ — they persist in landfill sites for hundreds of years ✓
- Burning/incinerating plastics can release toxic gases ✓ — e.g., PVC releases hydrogen chloride (HCl); incomplete combustion releases CO ✓
- Plastics in oceans harm marine life ✓ — animals ingest plastics or become entangled ✓
Example 4: Natural Polymers
Question: Starch and cellulose are both polymers of glucose. Explain why humans can digest starch but not cellulose. [2 marks]
Solution (model answer):
- Starch and cellulose have different linkages between glucose units (alpha vs beta glycosidic bonds) ✓
- Humans have enzymes that can break down starch (amylase) but not the beta linkages in cellulose ✓
Practice Questions
-
Draw the repeating unit of poly(chloroethene) (PVC). [2 marks]
-
Name the monomer used to make PTFE. [1 mark]
-
Explain the difference between addition and condensation polymerisation. [3 marks]
-
State one use for each of: (a) poly(propene), (b) PVC, (c) PTFE. [3 marks]
-
A polymer has the repeating unit -(CH2-CF2)-. Draw the displayed formula of its monomer. [2 marks]
-
Describe two environmental problems caused by the disposal of plastics and suggest one solution. [4 marks]
Key Facts to Memorise
- Addition polymerisation: alkene monomers (C=C) join; no byproduct; repeating unit has no double bond
- Ethene → poly(ethene): -(CH2-CH2)-
- Propene → poly(propene): -(CH2-CHCH3)-
- Chloroethene → PVC: -(CH2-CHCl)-
- Tetrafluoroethene → PTFE: -(CF2-CF2)-
- Condensation polymerisation: monomers join + small molecule (water) eliminated
- Terylene = polyester; Nylon = polyamide
- Natural polymers: proteins (amino acids), starch and cellulose (glucose), DNA (nucleotides)
- Plastics are non-biodegradable → landfill, ocean pollution, toxic gases from incineration
Common Misconceptions
| Students often think… | But the correct understanding is… |
|---|---|
| ”The repeating unit has a double bond like the monomer” | The double bond OPENS during polymerisation — the repeating unit has only single C-C bonds |
| ”All plastics are the same” | Different polymers have very different properties: poly(ethene) is flexible; PVC can be rigid; PTFE is non-stick |
| ”Burning plastics is always safe” | Incineration can release toxic gases: PVC → HCl; incomplete combustion → CO; some plastics release dioxins |
| ”Starch and cellulose are different polymers” | They are both made of glucose, but with different linkages (alpha vs beta) — this difference makes them fundamentally different in function and digestibility |
| ”The monomer of poly(propene) is propane” | The monomer is propene (CH2=CHCH3), an alkene. Propane is an alkane and does NOT undergo addition polymerisation |
| ”Condensation polymers always eliminate water” | While water is the most common byproduct, other small molecules like HCl can also be eliminated in some condensation reactions |
Key Concepts from Past Papers
Definitions You MUST Know (Exact Mark Scheme Wording)
- Polymer: a large molecule made from many small repeating units (monomers) joined together
- Monomer: a small molecule that can join with many others to form a polymer
- Addition polymerisation: monomers with C=C bonds join together without the formation of any other product
- Condensation polymerisation: monomers join together with the elimination of a small molecule (such as water)
Recurring Mark Scheme Answers
- “The double bond in the monomer opens to form single bonds in the polymer”
- “Addition polymers are non-biodegradable because microorganisms cannot break down the C-C bonds”
- “Burning PVC produces hydrogen chloride gas which is toxic/corrosive”
- (property on which fractional distillation) depends is the boiling point AND 1 mark each for any two of:
- idea of (fractional distillation) column
- petroleum heated / petroleum vaporised
- petroleum vapour enters at bottom of fractionating column
- temperatures high at bottom of column and low at the top
- different fractions / compounds move different distances
- vapour turns to liquid in condenser / vapour turns to liquid when it reaches a certain height
- with methane (aqueous) bromine remains orange with ethene (aqueous) bromine decolourised
Common Question Types
- Short recall (state/give/name): “Name the monomer used to make poly(propene)”
- Extended writing (describe/explain/suggest): “Explain why plastics cause environmental problems”
- Drawing: “Draw the repeating unit of PVC”
- Deduction: “Identify the monomer from the repeating unit -(CH2-CCl2)-”
- Comparison: “Compare addition and condensation polymerisation”
Exam Tips
- This topic appears in 28 papers in the database
- Total Q+A entries: 66
- Average marks per question: 1.0
- When drawing repeating units, ALWAYS show the bonds extending through the brackets on both sides: -[unit]-. Missing these bonds costs a mark
- The term “poly(ethene)” uses parentheses around the monomer name — this is the IGCSE convention
- For the monomer/repeating unit conversion: the key is that the C=C double bond becomes a C-C single bond in the polymer
- When answering pollution questions, be specific about which gas is produced from which polymer (PVC → HCl is the most commonly tested)
Keywords from Past Papers
methane, ethene, point, bonds, carbon, fractions, addition, energy, hydrocarbons, boiling, idea, structure, water, alcohol, poly
Related Notes
- Organic Chemistry Fundamentals — Functional groups, homologous series
- Alkanes — Saturated hydrocarbons
- Alkenes — Unsaturated hydrocarbons (monomers for addition polymers)
- Alcohols — Ethanol, propanol
- Esters — Condensation polymerisation to form polyesters
- Fuels and Petroleum — Crude oil as the source of monomers
- Climate Change and Greenhouse Gases — CO2 from incineration
- IGCSE-Chem-Index — Full IGCSE Chemistry index
Sources
- OpenStax Chemistry 2e — [Chapter 20: Organic Chemistry (Polymers)], Rice University (free, CC BY 4.0)
- BBC Bitesize GCSE Chemistry — [Polymers], BBC (free educational resource)
- Cambridge IGCSE Chemistry 0620 — Syllabus Section 11: Organic Chemistry (Polymers), Cambridge Assessment International Education
- CK-12 Chemistry for High School — [Chapter 25: Polymers], CK-12 Foundation (free, CC BY-NC 3.0)
Past Paper Sources
- 0620/32 Feb/March 2017: Q33(b)(iv) (1m), Q33(c)(iii) (1m)
- 0620/32 Feb/March 2018: Q66(a)(i) (1m)
- 0620/32 Feb/March 2019: Q55(d)(iii) (1m)
- 0620/32 Feb/March 2020: Q11(a)(ii) (1m), Q11(a)(v) (1m)
- 0620/32 Feb/March 2021: Q66(c)(i) (1m)
- 0620/32 Feb/March 2022: Q22(a)(ii) (2m), Q77(b)(i) (1m)
- 0620/32 Feb/March 2023: Q66(a)(iv) (2m)
- 0620/32 May/June 2018: Q11(a)(v) (1m), Q33(a)(iv) (1m), Q33(c)(ii) (0m)
- 0620/33 May/June 2016: Q44(c)(iv) (1m), Q66(e)(i) (1m)
- 0620/33 May/June 2017: Q44(a)(ii) (1m)
- 0620/33 May/June 2019: Q11(a)(i) (2m), Q11(a)(iv) (1m), Q11(a)(vi) (1m) (+3 more)
- 0620/33 May/June 2021: Q44(a)(iii) (1m), Q44(d)(i) (1m), Q44(d)(ii) (1m) (+1 more)