Everything on the GCSE Chemistry Polymers poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
Addition polymerisation
Many small alkene monomers join end to end. The C=C double bond breaks open and forms single bonds with neighbouring monomers. No atoms are lost - the polymer contains the same atoms as the monomers.
The general equation shows n molecules of a monomer such as CH₂=CH₂ joining to form a long-chain polymer: (CH₂-CH₂)ₙ.
Examples
- Poly(ethene) - plastic bags and bottles
- Poly(propene) - ropes and crates
- Poly(chloroethene) (PVC) - drainpipes and window frames
- PTFE - non-stick coating
Condensation polymers
Monomers with two functional groups join together, releasing a small molecule (water) each time a bond forms.
Polyesters
A diol and a dicarboxylic acid react to form a polyester and water. Two ester linkages form per repeat unit, so the byproduct is 2H₂O. Ester bonds form between the -OH group of the diol and the -COOH group of the dicarboxylic acid.
The reaction can be written as:
HO-[diol]-OH + n C(=O)-[dicarboxylic acid]-C(=O) → [-O-[diol]-O-C(=O)-[dicarboxylic acid]-C(=O)-]ₙ + 2nH₂O
Polypeptides (proteins)
Amino acids (e.g. glycine) each have an amino group (-NH₂) and a carboxylic acid group (-COOH) on the same molecule. They join via condensation to form polypeptides - proteins are one or more polypeptide chains. One amide linkage forms per bond, releasing H₂O.
Disposal issues
- Most synthetic polymers are non-biodegradable, so they build up in landfill.
- Burning releases toxic gases (including HCl from PVC and CO from incomplete combustion).
- Plastic waste accumulates in oceans.
- Biopolyesters and recycling reduce environmental impact.