Predicting the type of polymerisation
Introduced| English | Meaning |
|---|---|
| monomer/ˈmɒnəʊmə/ | A molecule that can join with other molecules to form a polymer. |
| addition polymerisation/əˈdɪʃn ˌpɒlɪməraɪˈzeɪʃn/ | The joining of unsaturated monomers into a polymer without forming a separate small-molecule product. |
| functional group/ˈfʌŋkʃənl ɡruːp/ | An atom or group of atoms responsible for characteristic chemical reactions of an organic compound. |
| condensation polymerisation/kɒndenˈseɪʃn ˌpɒlɪməraɪˈzeɪʃn/ | Polymerisation in which monomers join with the loss of a small molecule such as water. |
Which kind of polymer?
- Monomers 单体 can join in two very different ways.
- One clue — the monomer itself — tells you which.
- It comes down to whether a C=C opens up, or a small molecule is lost.
Polymerisation type lab
Classify monomers by whether they form addition or condensation polymers.
Two monomers each with two functional groups will most likely form by:
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Two reactive ends per monomer link with loss of a small molecule.
Addition polymers form from monomers with C=C double bonds and release water as each link forms.
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False. Addition polymerisation has no by-product: all the monomer atoms end up in the polymer. Losing a small molecule such as water happens in condensation polymerisation.
The clues
| Clue | Type |
|---|---|
| monomer has a C=C and nothing is lost | addition polymerisation 加成聚合 |
| each monomer has two functional groups 官能团, a small molecule is lost, the chain has ester/amide links | condensation polymerisation 缩合聚合 |
Addition versus condensation polymerisation
A monomer with a C=C double bond, where nothing else is lost, undergoes:
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Addition polymerisation opens the C=C and joins monomers with no other product.
Monomers with two functional groups that lose a small molecule give:
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Two-group monomers join with loss of a small molecule, forming ester/amide links — condensation.
A polymer chain that contains ester or amide links was made by:
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Ester/amide links are the signature of condensation polymers (addition polymers have a plain C–C backbone).
Match each term to its meaning.
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Each item links the term to its correct meaning.
How to tell the type
- Look at the monomer, not just the polymer.
- One monomer with a C=C → addition. Two monomers each with two reactive groups → condensation.
- Condensation always loses a small molecule (water, or HCl from an acyl chloride).
- Addition: ethene CH₂=CH₂ → poly(ethene). The double bond opens; nothing is lost.
- Condensation (polyester): a diol + a dicarboxylic acid → PET + water (ester links).
- Condensation (polyamide): a diamine + a dicarboxylic acid → nylon + water (amide links).
A single C=C monomer is the give-away for addition; two double-ended monomers losing water/HCl is condensation.
Spotting the repeat unit
- Addition polymer: the backbone is all carbon — no links break it up.
- Condensation polymer: you can spot ester (–COO–) or amide (–CONH–) links repeating along the chain.
- Finding those links in a structure instantly tells you it was made by condensation.
You've got it
- addition: a C=C monomer opens up, nothing else is lost (e.g. poly(ethene))
- condensation: two-group monomers join, a small molecule is lost (water/HCl), leaving ester/amide links (e.g. PET, nylon)
- to decide: look at the monomer and check for a lost small molecule