Polymers — Chemistry, 11–13
A polymer is a very large molecule made from many smaller repeating units, giving materials such as plastics and fibres their useful properties.
Molecular chains
Imagine linking thousands of small paper clips into a long chain. A polymer is like that at molecular scale: many smaller units join into a huge chain or network. The chain’s length, branches and links help decide whether the material is stretchy, hard, light or strong.
Why make polymers?
People needed materials that were light, waterproof, flexible or easy to shape, but natural materials could not always provide enough. Chemists learned to join small molecules into long chains with chosen properties. This solved practical design problems, although making and discarding some polymers can create environmental problems.
From ethene to polythene
Ethene has the formula C₂H₄ and a double bond that can open. Step 1: many ethene molecules line up. Step 2: each double bond opens and joins the next molecule. Step 3: a long chain forms, called polyethene, written (–CH₂–CH₂–)ₙ. The n means the pair repeats many times.
One giant molecule or many?
It is easy to picture a plastic bag as one solid thing, so you may think it is one enormous molecule. The bag is actually made of many polymer molecules packed together, often with additives. A single polymer molecule can be very large, but the whole object is still a collection of molecules.
Clothes, packaging and medicine
Polymers are found in fleece clothing, food packaging, phone cases, paints and contact lenses. Their chains can be designed for different jobs, such as keeping water out or stretching without tearing. Not every polymer is plastic: natural materials such as wool, silk and cellulose are polymers too.
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