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Plastics are long chains of small molecules. Why does a chain curl up, and why is it stretchy?
Polymer Chains lab · Last updated: 16 October 2026
You build a long chain from many small molecules, the way plastics are made, and watch it wriggle and curl up into a tangle. Then they pull it straight and let go.
What you'll discover
- A polymer is a very long chain made by joining thousands of small molecules called monomers.
- A jiggling chain is far more likely to be found curled up than stretched out straight.
- Pulling straightens the chain, and when you let go the jiggling curls it up again, which makes it stretchy.
The science in plain words
Polymers are giant molecules made of many small units, called monomers, joined end to end. Polythene, the plastic in carrier bags, is made by joining thousands of ethene molecules into one long chain of carbon atoms. Nature makes polymers too: starch and cellulose are chains of sugar units, proteins are chains of amino acids, and DNA is a chain of nucleotides.
Each link in a chain can twist and turn, and at any temperature above absolute zero the chain is constantly jiggling. There is only one way for a chain to be perfectly straight, but there are an enormous number of ways for it to be curled and tangled. So as the chain jiggles about at random, it almost always ends up coiled, simply because coiled shapes are so much more likely.
When you pull on the chain, you straighten it out into one of the few stretched shapes. Let go, and the random jiggling quickly scrambles it back into a coil. This is the main reason rubber is elastic. In a rubber band, many chains are tangled and lightly linked to each other, so they can stretch a long way and still spring back. Surprisingly, a stretched rubber band shrinks when warmed, because faster jiggling pulls the chains back into coils more strongly. Plastics whose chains slide past each other easily can stretch and stay stretched instead.
Where it fits
- India, NCERT: Class 10 science, Chapter 4: Carbon and its Compounds
- India, NCERT: Polymer elasticity goes beyond the NCERT syllabus for classes 6 to 10; the lab builds on carbon chains in Class 10 Carbon and its Compounds.
- United States: Grades 6 to 12
- Next Generation Science Standards: MS-PS1-3, HS-PS2-6
Common questions
What is a polymer?
A polymer is a very large molecule made of many small repeating units, called monomers, joined in a long chain. Plastics such as polythene and nylon are synthetic polymers. Starch, cellulose, rubber, proteins and DNA are natural polymers made by living things.
Why is rubber stretchy?
Rubber is made of long, tangled polymer chains that are coiled up and lightly linked together. Pulling straightens the chains. When you let go, their constant random jiggling curls them back up, because coiled shapes are far more likely than straight ones, so the rubber springs back.
Are all plastics polymers?
Yes. All plastics are made of polymers, usually long chains built mainly from carbon atoms. Different monomers and different ways of joining the chains give plastics their different properties, from soft and stretchy polythene to hard, rigid materials used in helmets and pipes.
Related labs
- Protein Folding: A protein is a long chain. How does it fold itself into exactly the right shape?
- Molecular Bonding: What holds two atoms together, and how hard do you have to shake them to break it?
- DNA Replication: Before a cell divides it copies all its DNA. How does it copy it so well?
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Try it yourself
The Polymer Chains lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.