Synthetic and naturally occurring polymers (chemistry only)

7.3.1 Addition polymerisation

  • Alkenes can be used to make polymers eg poly(ethene) by addition polymerisation
  • In addition polymerization reactions, many small molecules (monomers) join tgt to form large molecules (polymers)

Some carrier bags are made from poly(ethene). Some carrier bags are made from cornstarch. Suggest two benefits of using cornstarch instead of poly(ethene) to make carrier bags. (2)

  • (Polymers made from) cornstarch are biodegradable
  • Less space needed in landfill sites
  • Polymers from cornstarch come from a renewable source


  • Simple properties eg strong / low density / water resistant
  • Bags can be reused (for shopping) or another specified use eg bin liners
  • Money charged for bags can go to good causes or encourage reuse
  • Poly(ethene) bags can be recycled eg made into milk bottle crates
  • Poly(ethene) bags can be burned to provide heat for buildings/generation of electricity
  • New bags are now made that can biodegrade


  • (Older) bags can take many years to biodegrade
  • There is a shortage of landfill space
  • Bags are made from (crude) oil which is a non-renewable resource/running out
  • Large amounts of energy/fuel are used for the production of poly(ethene)
  • Production of poly(ethene) releases carbon dioxide/causes global warming
  • Specified issue caused by litter eg visual pollution or effect on wildlife
  • Burning bags release carbon dioxide / causes global warming

Level 3 (5-6 marks) There is a detailed description of both advantages and disadvantages caused by using plastic shopping bags made from poly(ethene)

7.3.2 Condensation polymerisation (HT only)

Condensation polymerisation

  • Involves monomers with 2 functional groups
  • When these types of monomers react they join tgt (usually losing small molecules eg H2O)
  • Simplest polymers are produced from 2 different monomers with 2 of the same functional groups on each monomerFor exampleEthane diol
  • Hexanedioic acid


Polymerise to produce a polyester

7.3.3 Amino acids (HT only)

  • Have 2 different functional groups
  • React by condensation polymerisation to produce polypeptides

For example

              Glycine is H2NCH2COOH and polymerises to produce the polypeptide

  • Different amino acids can be combined in the same chain to produce protein

7.3.4 DNA (deoxyribonucleic acid) and other naturally occurring polymers

  • DNA (deoxyribonucleic acid) encodes genetic instructions for the development and functioning of living organisms and viruses
  • Double helix – 2 polymer chains, made from 4 different monomers called nucleotides
  • Polymers Monomers
    Starch Glucose
    Cellulose Glucose
    Proteins Amino acid