Polymers
CIE IGCSE ChemistryΒ· Section 11.8Β· 25 min read
1. 1. Core: Polymer Fundamentalsβ β ββββ± 5 min
Polymers are very large macromolecules made by joining hundreds or thousands of small, reactive molecules called monomers. They are classified into two groups: natural polymers (e.g. starch, cellulose, proteins) and synthetic polymers (e.g. plastics, nylon, polyester).
Polymer
Large long-chain molecule formed by covalently bonding many small monomer units
Example:
Poly(ethene) is made from thousands of ethene monomers bonded together
Classify each of the following as a monomer or polymer: a) Ethene, b) Nylon, c) Glucose, d) Starch
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Recall that monomers are small reactive building blocks, while polymers are large long-chain molecules.
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a) Ethene is a small unsaturated hydrocarbon: monomer
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b) Nylon is a long-chain synthetic plastic: polymer
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c) Glucose is a small sugar that builds starch: monomer
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d) Starch is a large natural carbohydrate made from glucose: polymer
Exam tip:
Always use the systematic IUPAC name for polymers (e.g. poly(ethene) not polythene, poly(chloroethene) not PVC) to score full marks.
2. 2. Core: Addition Polymerisationβ β β βββ± 8 min
Addition polymerisation occurs when many unsaturated alkene monomers join together. The double bond in each alkene breaks, and each monomer forms single covalent bonds to adjacent monomers, forming a continuous long polymer chain. No other products are formed in this reaction.
Addition Polymerisation
Reaction where unsaturated alkene monomers join to form a single polymer product with no by-products
Example:
Ethene monomers polymerise to form flexible, durable poly(ethene) used for plastic bags and packaging
Draw the repeat unit of poly(propene), formed from propene monomers with the structure
- 1
First, write the propene monomer structure, showing the double bond between the two carbon atoms:
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Break the double bond, and add single bonds extending out from the two main carbon atoms (these connect to adjacent repeat units):
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Enclose the structure in square brackets, with a bond extending through each bracket, and add the subscript n to show repeated units:
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Exam tip:
The subscript 'n' outside the repeat unit bracket is a required marking point; never omit it in your answers.
3. 3. Extended Only: Condensation Polymerisationβ β β β βExtended onlyβ± 7 min
Condensation polymerisation forms polymers when monomers with two functional groups react together. Each time two monomers join, a small molecule (most commonly water) is released as a by-product. The two main condensation polymers you need to know are polyesters (e.g. PET, used for plastic bottles) and polyamides (e.g. nylon, used for clothing and rope).
Condensation Polymerisation
Reaction where monomers with two functional groups bond to form a polymer, releasing a small by-product (e.g. water)
Example:
Ethane diol reacts with a dicarboxylic acid to form a polyester such as PET, releasing water as a by-product
Nylon is a polyamide formed from hexanedioic acid () and hexane-1,6-diamine (). Name the by-product formed, and state one difference between condensation and addition polymerisation.
- 1
Identify the functional groups: carboxylic acid (-COOH) on hexanedioic acid, amine (-NH_2) on hexane-1,6-diamine.
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When these groups react, an -OH from the carboxylic acid and an -H from the amine join to form the by-product: water ().
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Key difference: Addition polymerisation produces only the polymer as product, while condensation polymerisation produces the polymer plus a small by-product.
Exam tip:
You will only be asked to draw simple repeat units for polyesters/polyamides, or compare the two polymerisation types for Extended papers. No complex structural drawing is required.
4. 4. Core + Extended: Polymer Uses and Environmental Impactβ β β βββ± 5 min
Synthetic polymers are widely used because they are cheap, strong, durable, and resistant to chemical attack. Common uses include packaging (poly(ethene)), drink bottles (PET), clothing (nylon/polyester), and construction materials (poly(chloroethene)). Their durability, however, creates major environmental challenges:
Most synthetic polymers are non-biodegradable, taking hundreds of years to break down in landfills and oceans
Burning plastic waste releases toxic gases (e.g. hydrogen chloride from PVC) that cause air pollution and respiratory harm
Recycling polymers reduces waste, but requires expensive separation of different polymer types first
Biodegradable polymers made from renewable plant starch break down easily in the environment, reducing plastic waste accumulation
State two advantages and two disadvantages of using synthetic polymers for food packaging.
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Advantages: 1) They are waterproof and strong, protecting food from damage and moisture. 2) They are low-cost to produce in large quantities.
- 2
Disadvantages: 1) Most are non-biodegradable, creating persistent plastic waste after use. 2) They are usually made from finite crude oil resources.
5. Common Pitfalls
Wrong move:
Using common names (e.g. polythene, PVC) instead of systematic polymer names in answers
Why:
CIE examiners require IUPAC systematic names for full marks
Correct move:
Always use the format poly(monomer name): e.g. poly(ethene), poly(chloroethene)
Wrong move:
Omitting the subscript 'n' outside the square bracket when drawing polymer repeat units
Why:
The 'n' indicates the repeat unit is repeated many times, and is a mandatory marking point
Correct move:
Always add a small 'n' outside the closing bracket of any repeat unit you draw
Wrong move:
Stating condensation polymerisation produces no by-products (Extended only)
Why:
No by-products is a feature of addition polymerisation, not condensation
Correct move:
Remember condensation polymerisation always releases a small by-product, most commonly water
Wrong move:
Claiming all synthetic polymers are made from renewable resources
Why:
Most traditional synthetic polymers are derived from finite crude oil reserves
Correct move:
Only modern biodegradable polymers are typically made from renewable plant-based raw materials
Wrong move:
Drawing addition polymer repeat units with an intact double bond between main chain carbon atoms
Why:
The double bond in the alkene monomer breaks fully during addition polymerisation to form single bonds to adjacent monomers
Correct move:
Ensure all bonds between main chain carbon atoms in addition polymer repeat units are single covalent bonds
6. Quick Reference Cheatsheet
Polymer Type | Monomer Type | By-product? | Tier | Common Example |
|---|---|---|---|---|
Addition | Unsaturated alkenes | No | Core | Poly(ethene) from ethene |
Condensation (Polyester) | Diol + dicarboxylic acid | Water | Extended | PET from ethane diol + a dicarboxylic acid |
Condensation (Polyamide) | Diamine + dicarboxylic acid | Water | Extended | Nylon from hexane diamine + hexanedioic acid |
Natural | E.g. glucose, amino acids | Water | Core | Starch from glucose, protein from amino acids |
7. Frequently Asked
Do I need to learn polymer reaction mechanisms for 0620?
No. Reaction mechanisms are out of scope for IGCSE Chemistry 0620. You only need to describe reactions, draw repeat units, and identify monomers.
What is the key difference between addition and condensation polymers?
Addition polymers form from unsaturated alkene monomers with no by-products. Condensation polymers (Extended only) form from monomers with two functional groups, releasing small by-products like water.
Are all synthetic polymers non-biodegradable?
Most traditional synthetic polymers (e.g. poly(ethene)) are non-biodegradable, but modern biodegradable alternatives made from plant starch are now widely available.
Going deeper
What's Next
You have now completed the polymers topic and core content of the CIE IGCSE 0620 organic chemistry unit. Next, revise the full organic chemistry reaction summary to connect all functional groups and reactions you have learned, then practice structured past paper questions on organic chemistry to test your knowledge. For Extended students, ensure you also review mole calculations for organic compounds, which are often combined with organic reaction questions in Paper 4. Finally, move on to the chemical analysis unit to complete your full 0620 syllabus revision.