Polymers — Chemistry, 14–17 years
Many small molecules can join into long chains whose properties make materials such as plastic, rubber and nylon.
Molecular chains
A polymer is a very large molecule made by joining many smaller molecules called monomers. Like repeated links in a chain, the units can form long strands or networks; the exact links and their arrangement give the material its strength, flexibility or softness.
Why make polymers
Small molecules are often gases or liquids, but joining them can produce a solid with useful properties. Chemists learned to control chain length and branching to make materials that were light, waterproof or tough. The aim was not simply to make bigger molecules, but better materials.
Making polyethene
Ethene has the formula CH₂=CH₂, with a double bond. In addition, pressure and a catalyst open that bond, allowing molecules to join: n CH₂=CH₂ becomes –[CH₂–CH₂]–n. The repeating unit is C₂H₄, while n tells us that the chain contains many units.
Plastic is not one substance
It is reasonable to call every plastic object “plastic”, but chemistry uses the word for many different polymers. Polyethene, PVC and nylon have different structures and additives, so they do not melt, break down or recycle in the same way.
Materials around us
Polymer design appears in food packaging, waterproof clothing, contact lenses, car parts and medical devices. Some polymers are chosen for flexibility, others for strength or chemical resistance. A responsible choice also considers how long the object is used and what happens after disposal.
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