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11.8Organic Chemistry

Polymers — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 11 parts Lesson 8 of 10 1 quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Lesson summary

11.8 Polymers — Notes — IGCSE Chemistry notes: Describe addition and condensation polymers, plastics and their disposal, and proteins.Polymer — a large molecule built up from many smaller molecules called monomers.Bonding — each monomer is joined to the next by covalent bonds.Exa…

  • Poly(ethene)
  • Monomer from polymer
  • Condensation polymerisation
  • Difference from addition
  • Amino acids
  • Link formation

Part 1 of 9Polymers and monomers

Polymer
  • Polymer a large molecule built up from many smaller molecules called monomers.
Bonding
  • Bonding each monomer is joined to the next by covalent bonds.
Examples — poly(ethene) and PVC are addition polymers, and nylon is a condensation polymer.

Part 2 of 9Addition polymerisation

1Monomers
  • Monomers alkenes, which contain a C=C double bond.
2Process
  • Process one bond in each C=C breaks and forms a bond with the adjacent monomer, giving a polymer that contains only single bonds and only one product.
3Poly(ethene)
  • Poly(ethene) formed from many ethene monomers.
4Naming
  • Naming put the monomer name in brackets with poly- before it, such as poly(propene).

Part 3 of 9Examples of addition polymers

MonomerPolymerUse
EthenePoly(ethene)Plastic bags, bottles
PropenePoly(propene)Ropes, crates
ChloroethenePoly(chloroethene), PVCPipes, window frames, cable insulation
TetrafluoroethenePTFENon-stick pans
  • Equation
    • n CH2=CH2 → –[CH2–CH2]n–.

Part 4 of 9Repeat units (Extended)

To draw a repeat unit, change the double bond in the monomer to a single bond.
Add a continuation bond at each end, extending outside the brackets.
Write a small n at the bottom right of the brackets.
Keep the other groups in the same order as around the double bond.
Monomer from polymer
  • Monomer from polymer identify the repeat unit, change the single bond to a double bond and remove the continuation bonds.
The repeat unit of CH2=CH2 is –CH2–CH2–, of CH2=CHCH3 is –CH2–CH(CH3)– and of CH2=CHCl is –CH2–CHCl–.

Part 5 of 9Condensation polymers (Extended)

1Condensation polymerisation
  • Condensation polymerisation two different monomers join with the loss of a small molecule, usually water.
2Difference from addition
  • Difference from addition addition forms only the polymer, while condensation forms the polymer and one water molecule per link.
3Monomers
  • Monomers each has a functional group at both ends.
4Nylon
  • Nylon a polyamide made from a dicarboxylic acid and a diamine, with an amide linkage formed with loss of water.
5PET
  • PET a polyester made from a dicarboxylic acid and a diol, with an ester linkage formed with loss of water.
6
PET is used in plastic bottles and in synthetic fibres sold as terylene.

Part 6 of 9Proteins (Extended)

Proteins
  • Proteins condensation polymers made from amino acid monomers joined by amide (peptide) links, so they are natural polyamides.
Amino acids
  • Amino acids small molecules containing NH2 and COOH groups with a side chain R.
There are twenty common amino acids.
Proteins contain between 60 and 600 amino acids in different orders.
Link formation
  • Link formation the –COOH group of one amino acid reacts with the –NH2 group of another, and one water molecule is eliminated at each link.
Peptide link
  • Peptide link the –CO–NH– amide link in a protein is called a peptide link, and the long chain formed by repeating the reaction is a polypeptide.
Simplified diagrams
  • Simplified diagrams boxes represent the carbon-containing part of each amino acid, joined by the –CO–NH– peptide links.

Part 7 of 9Plastics and their disposal

Plastics
  • Plastics are made from polymers, which are often chemically unreactive and so non-biodegradable.
Landfill
  • Landfill waste polymers take up valuable land because microorganisms cannot break them down.
Oceans
  • Oceans plastic waste accumulates and disrupts marine life.
Incineration
  • Incineration polymers release heat but produce carbon dioxide, a greenhouse gas.
PVC releases toxic hydrogen chloride when burned.
Incomplete combustion produces toxic carbon monoxide.
Options
  • Options waste plastic can be reused, recycled or burned for energy.

Part 8 of 9Recycling PET (Extended)

Problem
  • Problem the conditions needed to break down many polymers can degrade the monomers.
PET
  • PET is relatively easy to convert back into its monomers using enzymes or chemical catalysts and mild heating.
Re-polymerisation
  • Re-polymerisation the monomers are recovered and re-polymerised into new PET, saving resources and energy.

Part 9 of 9More from the specification

1Macromolecular chain repeat units
  • Macromolecular chain repeat units addition polymerization joins identical monomer units together into extensive macromolecules containing thousands of connected repeat units.
2Principles of Addition Polymerisation
  • Under high pressure and catalytic initiation, thousands of unsaturated alkene monomers add together by opening their carbon-carbon double bonds to form long, saturated carbon-chain macromolecules.
3Deducing the Repeat Unit from Monomers
  • The repeat unit of an addition polymer mirrors the monomer skeleton with the double bond replaced by a single bond and extension bonds penetrating brackets with an external subscript 'n' (e.g. ethene to poly(ethene)).
4Environmental Impact and Non-Biodegradability
  • Synthetic addition polymers possess extremely strong, chemically inert covalent carbon-carbon backbones that resist microbial degradation, persisting in landfill sites and marine ecosystems for centuries.

Key terms

TermMeaning
PolymerA large molecule built from many monomers.
MonomerA small molecule that joins to form a polymer.
Addition polymerA polymer made from alkene monomers that forms only the polymer.
Condensation polymerA polymer formed with loss of a small molecule such as water.
Non-biodegradableCannot be broken down by microorganisms.
Repeat unitThe smallest section repeated along a polymer chain.
Amino acida monomer with –NH2 and –COOH groups.
Peptide linkthe –CO–NH– amide link in proteins.
Polyamidea polymer joined by amide links, such as nylon and proteins.

Avoid these mistakes

1
Saying addition polymerisation produces water — it forms only the polymer
2
Saying the polymer contains C=C bonds — the double bonds are used up and the polymer has single bonds
3
Saying plastics rot away — most are non-biodegradable
4
Repeating the same linking group for nylon and PET — nylon has an amide link and PET an ester link
5
Saying proteins are addition polymers or have ester links — they are condensation polyamides with peptide links and water is lost at each link

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