In polymer chemistry

Polymer chemistry

Polymer chemistry or macromolecular chemistry is a multidisciplinary science that deals with the chemical synthesis and chemical properties of polymers or macromolecules. According to IUPAC recommendations, macromolecules refer to the individual molecular chains and are the domain of chemistry...

, a structural unit is a building block of a polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 chain. It is the result of a monomer

Monomer

A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

 which has been polymerized into a long chain.

There may be more than one structural unit in the repeat unit

Repeat unit

An essential concept which defines polymer structure, the repeat unit or repeating unit is a part of a polymer chain whose repetition would produce the complete polymer by linking the repeat units together successively along the chain, like the beads of a necklace.A repeat unit is sometimes called...

. When different monomers are polymerized, a copolymer is formed. It is a routine way of developing new properties for new materials.

Example

Consider the example of polyethylene terephthalate

Polyethylene terephthalate

Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...

 (PET or "polyester"). The monomers which could be used to create this polymer are ethylene glycol

Ethylene glycol

Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...

 and terephthalic acid

Terephthalic acid

Terephthalic acid is the organic compound with formula C6H42. This colourless solid is a commodity chemical, used principally as a precursor to the polyester PET, used to make clothing and plastic bottles. Several billion kilograms are produced annually...

:

HO-CH₂-CH₂-OH
and
HOOC-C₆H₄-COOH

In the polymer, there are two structural units, which are
-O-CH₂-CH₂-O-
and
-CO-C₆H₄-CO-

The repeat unit is

-CH₂-CH₂-O-CO-C₆H₄-CO-O-