Definitions

A polymer is a large molecule built from many smaller molecules called monomers. A repeat unit is the smallest section that repeats along the polymer chain.

Representing a repeat unit

Polymer structures use brackets with bonds passing through both sides and a subscript n. The continuation bonds show that the chain extends beyond the drawn unit.

Linkages

A linkage is the characteristic group joining monomer residues. Addition polymers have a carbon-carbon backbone, polyesters contain ester links and polyamides contain amide links.

Reading polymer diagrams

Identify the backbone, locate repeated patterns and distinguish side groups from linking groups. The repeat unit may be shown more than once in a structure; choose the smallest chemically valid repeating section.

High-value recall and connections

Essential recall: What is a monomer? A small molecule that joins with many others to form a polymer. What does n mean? A large number of repeat units. Name the linkage in a polyamide. An amide linkage, -CONH-. Practical connection: Highlight repeat units and linkages in supplied polymer diagrams, then mark the continuation bonds. Examination connection: A repeat unit is not necessarily identical to the isolated monomer because bond changes occur during polymerisation.

Review questions and suggested answers