📘 Key Principle
Addition polymers form when monomers containing a C=C double bond undergo polymerisation. The π bond breaks, and the freed electrons form new C–C σ bonds to adjacent monomers. No atoms are lost – everything in the monomer appears in the polymer.
Common Addition Polymers
| Monomer | Polymer | Uses |
|---|---|---|
| Ethene (CH₂=CH₂) | Polyethene (PE) | Bags, bottles, packaging |
| Chloroethene (CH₂=CHCl) | PVC | Pipes, window frames, flooring |
| Tetrafluoroethene (CF₂=CF₂) | PTFE (Teflon) | Non-stick coatings, low friction |
| Phenylethene (CH₂=CHC₆H₅) | Polystyrene (PS) | Insulation, packaging foam |
Drawing Repeat Units
- Take the monomer and break the C=C into a C–C single bond
- Add extension bonds (dashes) at each end of the C–C backbone
- Enclose in square brackets with subscript n
For full marks: The repeat unit must have trailing bonds extending outside the square brackets and the subscript n. Missing either one loses the mark.
⚠️ Examiner Traps
- The repeat unit must show single bonds only – no C=C should remain
- The monomer must contain a C=C double bond – if it doesn't, it's not addition polymerisation
- Addition polymers are non-biodegradable – the saturated C–C backbone is chemically inert