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