The Chain Gang
📖 The Chain Gang
A polymer is like a chain made of paper clips — each clip is a monomer! You take small, identical units (monomers) and link them together into one long chain. The clips are held together firmly (covalent bonds), but different chains just loosely tangle together (weak intermolecular forces). That's why plastics can be flexible — the chains slide past each other!
The word "polymer" comes from Greek: "poly" means many, "mer" means parts. And that's exactly what they are — many small units (called monomers) joined together. Think of it like a paper chain: each loop is a monomer, and the whole chain is the polymer.
Polymers are covalently bonded molecules — the atoms within each chain are held together by strong covalent bonds. But like other simple molecular substances, the forces BETWEEN the chains are much weaker (intermolecular forces). This explains their properties:
- Relatively low melting points — only need to overcome weak intermolecular forces between chains
- Flexible — chains can slide past each other
- Insulators — no free electrons or ions to conduct
The amazing variety of plastics (soft and stretchy, hard and rigid, heat-resistant or heat-sensitive) comes from different monomers and different ways of arranging the chains.
Chemistry glossary
- What is a polymer?
- A large molecule made of many small repeating units (monomers) joined by covalent bonds
- What is a monomer?
- A small molecule that joins with others to form a polymer
Addition polymerisation is the most common way small molecules join to make polymers. It works like this:
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🧠 Memory Aids
MONO = one, POLY = many — like Monopoly! The board game Monopoly means "one seller" — mono (one) + poly (many properties, wait that doesn't quite work, but the mono/poly part sticks!). Monomer = one unit, Polymer = many units.
Addition polymerisation = ADD everything together: In addition polymerisation, ALL atoms are added into the chain — nothing is lost. All atoms from the monomers end up in the polymer.
Naming polymers: "poly" brackets + monomer name. Ethene → poly(ethene). Propene → poly(propene). If you forget which comes first, remember you ADD the poly AT THE START.
Drawing repeat units in exams: Start from the monomer (CH₂=CH₂), change the double bond to single (CH₂-CH₂), put brackets around it, and add little bonds sticking out at each end (—[CH₂-CH₂]ₙ—).
Now try it yourself
Quiz · Question 1 of 22
In addition polymerisation, what feature of monomer molecules allows them to join together?
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