Examo
PracticeAbout
HomechemistrySynthetic Polymers
4CH1

Synthetic Polymers

Organic Chemistry · 0 question types

Download PDF

4CH1 Topics

Introduction to Organic Chemistry3%
Crude Oil5%
Alkanes6%
Alkenes7%
Alcohols6%
Carboxylic Acids5%
Esters4%
Synthetic Polymers5%
  1. Addition Polymers
  2. Disposal of Addition Polymers
  3. Condensation Polymers

Frequency legend

High (≥14%)
Above avg (10 to 13%)
Average (<10%)

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 5% of your exam marks.

stable
Rare
Stable5%

Addition polymerisation (drawing repeat units, identifying monomers, common polymers + uses) and disposal / environmental impact regularly tested.

What a polymer is

  • A polymer is a very long molecule built by joining together a large number of small repeating units
  • The small repeating starting molecules are called monomers; each monomer becomes one repeat unit in the polymer chain
  • Polymerisation reactions join hundreds to thousands of monomers end-to-end through covalent bonds, giving a single chain molecule of high relative molecular mass
  • Synthetic polymers are manufactured by industry (plastics, nylon, polyester fabrics, polystyrene cups); natural polymers occur in living things (starch, cellulose, proteins, DNA)

Addition polymerisation

  • Addition polymerisation joins monomer molecules that each have a C=C double bond
  • One of the two bonds in the C=C of each monomer opens up; the spare bonds from neighbouring monomers link together to form a long single-bond chain
  • No other product is made — the polymer is the only outcome (compare with condensation polymerisation in section 3)
  • The molecular formula of the polymer is just n times the molecular formula of the monomer
  • General equation:

n CH2=CHR → −(CH2−CHR)−n

  • where R is whatever atom or group is attached to the second carbon of the monomer

The four named addition polymers

MonomerPolymerRepeat unitTypical use
Ethene, CH2=CH2Poly(ethene)−(CH2−CH2)−nPlastic bags, bottles, food wrap
Propene, CH2=CHCH3Poly(propene)−(CH2−CH(CH3))−nCrates, ropes, food containers
Chloroethene, CH2=CHCl (vinyl chloride)Poly(chloroethene) — PVC−(CH2−CHCl)−nDrainpipes, window frames, electrical cable insulation
Tetrafluoroethene, CF2=CF2Poly(tetrafluoroethene) — PTFE / Teflon−(CF2−CF2)−nNon-stick coatings, plumber's tape, low-friction bearings

Drawing a polymer's repeat unit from its monomer

  • A four-step recipe:
    • Write out the displayed formula of the monomer
    • Change the C=C double bond to a single C−C bond
    • Add a "stub" bond going outward from each carbon, sticking out of the brackets to show where the chain continues
    • Enclose the unit in brackets and write a subscript n outside the bracket
  • Worked example: poly(chloroethene) from chloroethene
    • Monomer: CH2=CHCl
    • Open the double bond to a single bond and add extension bonds: −(CH2−CHCl)−
    • Add the subscript: −(CH2−CHCl)−n

Reading the monomer from a polymer's repeat unit

  • Reverse the recipe: take the repeat unit, remove the extension bonds and the subscript n, and turn the C−C single bond between the two carbons back into a C=C double bond
  • Worked example: poly(propene) repeat unit −(CH2−CH(CH3))−n
    • Remove the brackets and the subscript: CH2−CH(CH3)
    • Put the double bond back: CH2=CH(CH3) — propene
  • This skill is exam-mark assessable in both directions: monomer → polymer and polymer → monomer

Previous

Practical: Preparation of Ethyl Ethanoate

Next

Disposal of Addition Polymers