Polymers

Polymers are large molecules made from repeating smaller units called monomers. They’re all around us — in plastic bottles, clothing, food packaging, and even your own body. This topic explores how polymers are made, the differences between types of polymerisation, and the natural polymers essential for life.

What Are Polymers and Plastics?

Polymers are long chains of repeating molecules. These chains are made by joining lots of monomers (small molecules) together. Most plastics are synthetic (man-made) polymers, and they’re designed for a wide range of uses — from waterproof materials to flexible packaging.

One of the most common ways to make polymers is through a process called polymerisation.

Addition Polymerisation

Addition polymerisation involves the joining of unsaturated monomers — specifically alkenes that contain a double carbon–carbon bond (C=C). During the reaction, the double bonds open up, and many monomers link together to form a long polymer chain.

For example:

• Ethene molecules → poly(ethene) (used in plastic bags and containers)

Only one type of monomer is needed for addition polymerisation, and the only product is the polymer itself — no other substance is formed.

Condensation Polymerisation

In condensation polymerisation, two different monomers with different functional groups react to form a polymer. Unlike addition polymerisation, this reaction also produces a small molecule like water as a by-product.

This process is how many naturally occurring polymers are formed, such as proteins and starches, as well as man-made materials like nylon and polyesters.

Natural Polymers in Biology

Polymers aren’t just found in plastics — they’re essential to life.

• Proteins are natural polymers made from long chains of amino acids. The sequence of amino acids determines the protein’s function, from building muscle to speeding up reactions as enzymes.
• DNA is a complex natural polymer made from units called nucleotides. It carries genetic information and is shaped like a double helix.
• Starch and cellulose are polymers made from sugars (simple carbohydrates). Starch is used by plants to store energy, while cellulose gives strength to plant cell walls.

These natural polymers are formed through condensation reactions — similar to synthetic condensation polymers but with biological molecules.

Also see Organic Reaction, Crude Oil & Fuels, Chemical Analysis

Links for Learning

Education Quizzes: Polymerisation
Bitesize: Condensation polymerisation
Pass my Exams: Condensation polymerisation
Bitesize: Addition polymerisation
Pass my Exams: Additon polymerisation