Identifying the Monomer

Given a section of an addition polymer, or its repeat unit, you can work backwards to find the monomer.In an addition polymer the main chain is made only of carbon atoms, and each monomer supplies two of them (the two carbons that were joined by the C=C). So:1. Pick out the repeat unit: two carbon atoms of the main chain together with the atoms and groups attached to them.
2. Remove the two bonds that extend out to the rest of the chain (the bonds through the brackets).
3. Put a double bond between the two carbon atoms.
4. Keep every side group exactly where it was.Examples:• -[CH₂-CH(CH₃)]- comes from CH₂=CHCH₃, propene
• -[CH₂-CHCl]- comes from CH₂=CHCl, chloroethene
• -[CF₂-CF₂]- comes from CF₂=CF₂, tetrafluoroethene
• -[CH₂-CH(C₆H₅)]- comes from CH₂=CHC₆H₅, phenylethene
• -[CH(CH₃)-CH(CH₃)]- comes from CH₃CH=CHCH₃, but-2-eneWorking from a longer section: look for the pattern that repeats every two main-chain carbons. For example, in-CH₂-CH(CN)-CH₂-CH(CN)-CH₂-CH(CN)-the unit CH₂-CH(CN) repeats, so the monomer is CH₂=CHCN (propenenitrile).Common trap: a side group such as CH₃ is not part of the main chain. In the but-2-ene example above the monomer has four carbons in total, but only two of them are in the chain; the CH₃ groups stay as branches.