Functionality (chemistry)

Methyl acetate

Thiophenol

Ethylamine

Malonic acid

Ethanolamine

Glycine

Glycerol

(R)-Cysteine

In chemistry, functionality is the presence of functional groups in a molecule. In organic chemistry (and other fields of chemistry) functionality of a molecule has a decisive influence on its reactivity. In polymer chemistry the functionality of a monomer means its number of polymerizable groups, it affects the formation and the degree of crosslinking of polymers.

A monofunctional molecule possesses one function, a difunctional two, a trifunctional three, etc.

In organic chemistry, functionality is often used as a synonym for functional group. For example, a hydroxyl group can also be called a HO-function.

Functionalisation means the introduction of functional groups, for example

According to IUPAC, the functionality of a monomer is defined as the number of bonds that a monomer's repeating unit forms in a polymer with other monomers. Thus in the case of a functionality of f = 2 a linear polymer is formed by polymerizing (a thermoplastic). Monomers with a functionality f ≥ 3 lead to a branching point, which can lead to cross-linked polymers (a thermosetting polymer). Monofunctional monomers do not exist as such molecules lead to a chain termination.

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