Addition polymerisation
Introduced| English | Meaning |
|---|---|
| addition polymerisation/əˈdɪʃn ˌpɒlɪməraɪˈzeɪʃn/ | The joining of unsaturated monomers into a polymer without forming a separate small-molecule product. |
| monomer/ˈmɒnəʊmə/ | A molecule that can join with other molecules to form a polymer. |
| polymer/ˈpɒlɪmə/ | A large molecule made from many linked repeating units derived from smaller molecules. |
| repeat unit/rɪˈpiːt ˈjuːnɪt/ | The smallest structural pattern that repeats along a polymer chain. |
| non-biodegradable/nɒn ˌbaɪəʊdɪˈɡreɪdəbl/ | Not broken down by microorganisms, so it persists in the environment. |
Plastics from double bonds
- In addition polymerisation 加成聚合, many small molecules join into one long chain — with no other product.
- Each small molecule is a monomer 单体; it must have a C=C double bond.
- The long chain is the polymer 聚合物.
Addition polymerisation route
Watch alkene monomers join by opening their double bonds.
In addition polymerisation, the monomers must have:
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The C=C double bond opens up to let the monomers link into a long chain, with no other product.
Addition polymers are made from monomers containing a C=C ______ bond.
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The double bond opens to join the units.
Repeat units 重复单元
- The repeat unit is the small part copied along the chain. To find it: change the C=C to a single C–C and draw bonds out at each end.
$$n\,\text{CH}_2{=}\text{CH}_2 \rightarrow -(\text{CH}_2{-}\text{CH}_2)_n-$$
- Examples: poly(ethene) from ethene; poly(chloroethene) (PVC) from chloroethene.
Most addition polymers are non-biodegradable 不可生物降解, so they build up as waste.
Poly(alkene) waste is non-biodegradable and burning PVC gives toxic HCl
To draw the repeat unit from a monomer, you:
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Open the double bond (C=C → C–C) and put a bond out at each end to show the chain continues.
Match each addition-polymer fact.
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Each item links the term to its correct meaning.
Making poly(ethene) by addition polymerisation also produces water.
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The monomer atoms all enter the polymer. Addition polymerisation has no small-molecule by-product.
Finding the monomer
- Go the other way: take one repeat unit and put the C=C double bond back.
- That gives you the monomer.
Poly(ethene) is supplied as tiny pellets a few millimetres across, which are then melted and moulded into bottles, bags and other products
To find the monomer from a polymer's repeat unit, you:
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Reversing the process, restore the C=C double bond in one repeat unit to get the monomer.
The repeat unit –CH₂–CH(CH₃)– comes from the monomer ____.
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Restore the C=C between the two backbone carbons: CH₂=CHCH₃, which is propene.
The repeat unit –CH₂–CH(CH₃)– contains how many carbon atoms?
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Two carbons form the backbone and one is in the methyl side group: three in total.
The disposal problem
- Poly(alkene)s are non-biodegradable — microbes can't break them down, so they linger for a very long time.
- Burning them can release harmful gases — e.g. burning PVC gives off toxic hydrogen chloride.
Monomer and repeat unit for PVC
Why are poly(alkene)s hard to dispose of?
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Microbes cannot break them down (non-biodegradable); burning PVC releases toxic hydrogen chloride.
You've got it
- addition polymerisation: many C=C monomers join into one polymer (no other product)
- repeat unit: change the C=C to a single bond, bonds out at each end
- find the monomer by putting the C=C back
- poly(alkene)s are non-biodegradable; burning PVC releases toxic HCl