h - Synthetic polymers

4h (4.44-4.50)

Addition polymer

• Polymers are made by joining up lots of small repeating units called monomers
  The monomers that make up addition polymers have double covalent bond

• Lots of unsaturated monomer molecules can open up C=C double bonds + join to form polymer chains, called addition polymerisation

Naming + formula of polymers

• Name of from type of monomer it’s made from - put brackets around it + put ‘poly’ in front
  e.g. propene → poly(propene)

• To get formula of polymer, put formula of monomer in brackets + put a small ‘n’ after
  e.g. C₃H₆ → (C₃H₆)ₙ

How to draw repeat unit of polymer

• Join carbons together in a row with no double bonds, put pair of brackets around repeating unit, and put an ‘n’ after

• Draw a bond from each of 2 carbons in chain that pass through brackets - shows that chain continues

• To get displayed formula of monomer from displayed formula of polymer, do the reverse

• Draw out the repeating unit of polymer, get rid of 2 bonds going out through brackets + put double bond between carbons

Problems with disposal of addition polymers

• Inert - don’t react easily because C-C bonds in polymer chain are very strong + not easily broken

  • so it takes long time for addition polymers to biodegrade (be broken down by bacteria/other organisms)

• Burning plastics can release toxic gases

  • so it’s difficult to dispose of polymers → best thing is to reuse then recycle

Condensation polymerisation

• Involved 2 different types of monomer

• Monomers react together + bonds form between them, making polymer chains

• Each monomer must contain at least 2 functional groups, one on each end of molecule

• Each functional group can react with functional group of another monomer, creating long chains of alternating monomers
  For each new bond formed, a small molecule (e.g. water) is lost

Polyesters

• Formed when dicarboxylic acid monomers + diol monomers react together

• Dicarboxylic acid monomers contain 2 carboxylic acid (-COOH) groups + diol monomers contain 2 alcohol (-OH) groups

• When carboxylic acid group reacts with alcohol group, forms ester link

• Polyesters are condensation polymers - each time ester link forms, a molecule of water is lost

Biopolyesters

Biodegradable polyesters, known as biopolyesters, can be broken down by bacteria + other living organisms in environment over time

They decompose + don’t stay in landfill forever, reducing polymers’ pollutant effect