# Polymer

A very long molecule made of many small repeating units (monomers) joined together. Plastics are polymers.

Chemistry (school) · Part 08: Carbon chemistry and the Earth · Card 7 of 10 · Last updated 2026-10-19

## Analogy

A polymer is like a long paper-clip chain. Each clip is a monomer.

## Example

**Addition polymer**

many ethene molecules
-> poly(ethene)
The double bond opens to join them.

## In practice

Many ethene molecules join to make poly(ethene), used in carrier bags and bottles.

## Questions people ask

### Why are plastics a problem for the environment?

Many addition polymers do not break down naturally, so they stay in landfill and oceans for hundreds of years. Animals can eat or become tangled in them. Recycling, reusing and biodegradable plastics help. Burning plastic can release harmful gases, so it needs careful control.

### What is a monomer?

A monomer is a small molecule that can join with many others to form a polymer. Ethene is the monomer of poly(ethene), and propene is the monomer of poly(propene). In addition polymerisation, the double bond opens and the monomers link end to end.

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