Monomers, polymers and repeat-unit representations

Monomers, polymers and repeat-unit representations

A polymer is a large molecule made from repeating smaller units called monomers. In addition polymerisation, an alkene double bond opens and many monomers link with no small molecule removed; draw the repeat unit in brackets and use n outside the bracket. In condensation polymerisation, functional groups on monomers react and a small molecule such as water or hydrogen chloride is eliminated. The repeat unit should show the link formed between monomers rather than simply placing whole monomer drawings side by side. Polymer properties depend on chain length, branching, cross-links and intermolecular forces, which in turn affect use and recycling challenges.

Work it through

Ethene monomers CH₂=CH₂ form poly(ethene) with repeat unit [−CH₂−CH₂−]ₙ. The double bond is not retained in each repeat unit because it opened to make bonds to neighbouring units. A correct polymer answer makes the bracket and n visible and distinguishes the monomer from the repeated segment.

Mastery target

Identify monomers and polymerisation type, draw or read a simple repeat unit and connect polymer structure to a cautious property or sustainability claim.