Polymers (DP IB Chemistry): Revision Note
Polymers
What are polymers?
Polymers are large molecules made by chemically linking many small molecules called monomers
A polymer must contain at least 50 repeating units
Each unit is joined to the next by strong covalent bonds
Polymers are also known as macromolecules due to their large size compared with simple molecules
Monomers forming polymers diagram

Some polymers contain just one type of monomer unit
Examples include poly(ethene) and poly(chloroethene), commonly known as PVC
Others contain two or more different types of monomer units and which are called copolymers
Examples include nylon and biological proteins
Addition polymerisation
In addition polymerisation, many monomers join together without forming any by-products
The monomers usually contain carbon–carbon double bonds (C=C), which break to form single bonds that link the units
The polymer poly(ethene) is formed from ethene monomers:

Poly(ethene) is made when many ethene molecules join together via addition polymerisation
The C=C double bonds open up and link into a chain
The structure of polymers is usually shown using:
A repeating unit in square brackets
An "n" outside, indicating a large number of monomer units
Properties of polymers
Plastics are made from long-chain molecules called polymers. Their structure gives them useful properties:
Low density – Polymer chains are loosely packed, so plastics are lightweight compared to metals or ceramics
Unreactive – Most plastics don’t react easily because the polymer chains are chemically stable
Water-resistant – Plastics repel water and don’t absorb moisture, making them ideal for containers and packaging
Strong – Polymers are held together by strong covalent bonds, making many plastics tough and durable
These properties make polymers useful in everyday materials such as packaging, clothing, construction products, and transportation components.
Natural and synthetic polymers
Natural polymers include proteins, starch and DNA
These are formed by living organisms from monomers like amino acids or nucleotides
DNA forms a double helix with millions of linked nucleotides
DNA is a natural polymer

Synthetic polymers include plastics like poly(ethene) and nylon
These are man-made and have widespread uses due to their durability, low reactivity, and water resistance
Environmental impact of synthetic polymers
Synthetic polymers are generally non-biodegradable because of their chemical stability
They do not break down naturally, leading to long-lasting pollution
The accumulation of plastics in the environment is a major global concern
Examiner Tips and Tricks
You don’t need to memorise full polymer structures, but you should be able to:
Describe how addition polymerisation works using alkenes
Recognise a repeating unit in a polymer chain
Deduce the monomer from a polymer structure (and vice versa)
Use examples like poly(ethene) or PVC to explain the properties and uses of plastics
Explain how polymer properties (e.g. strength, low reactivity, water resistance) relate to their structure
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