Polymers (DP IB Chemistry): Revision Note

Philippa Platt

Written by: Philippa Platt

Reviewed by: Richard Boole

Updated on

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

Diagram showing monomers in green ovals undergoing polymerisation to form a polymer chain.
Diagram showing how lots of monomers bond together to form a polymer
  • 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:

Diagram of polymerisation: ethene molecules with double bonds convert to poly(ethene) chains with single bonds.
Poly(ethene) is formed by addition polymerisation using 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

DNA is an example of a naturally occurring polymer
DNA molecules form a three-dimensional structure known as a DNA double helix. It is made from four different monomers known as nucleotides which join together in different combinations to make a long strand
  • 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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Philippa Platt

Author: Philippa Platt

Expertise: Chemistry Content Creator

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener

Richard Boole

Reviewer: Richard Boole

Expertise: Chemistry Content Creator

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

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