In
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
, functionality is the presence of
functional group
In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
s in a
molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
. A monofunctional molecule possesses one functional group, a
bifunctional (or difunctional) two, a trifunctional three, and so forth. In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
(and other fields of chemistry), a molecule's functionality has a decisive influence on its
reactivity.
In
polymer chemistry
Polymer chemistry is a sub-discipline of chemistry that focuses on the structures, chemical synthesis, and chemical and physical properties of polymers and macromolecules. The principles and methods used within polymer chemistry are also applic ...
, the functionality of a
monomer
A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization.
Classification
Chemis ...
refers to its number of
polymerizable groups, and affects the formation and the degree of
crosslinking of
polymers.
In organic chemistry and material science
In organic chemistry, functionality is often used as a synonym for
functional group
In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
. For example, a
hydroxyl group can also be called a HO-function.
''Functionalisation'' means the introduction of functional groups, for example
* the functionalisation of a surface (e.g.
silanization for the specific modification of the
adhesion
Adhesion is the tendency of dissimilar particles or interface (matter), surfaces to cling to one another. (Cohesion (chemistry), Cohesion refers to the tendency of similar or identical particles and surfaces to cling to one another.)
The ...
of a
surface)
* the functionalization of
nanoparticle
A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...
s of a metal or metal oxide to stabilize such nanoparticles
[Marie-Alexandra Neouze, Ulrich Schubert: Surface Modification and Functionalization of Metal and Metal Oxide Nanoparticles by Organic Ligands, Monatsh.] or
* the so-called
C-H functionalization, which means the substitution of a C-H bond by a functional group, bonded at the same carbon atom
In polymer chemistry
According to
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
, 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
A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains as ...
). 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.
[Eintrag zu ''functionality, f of a monomer''.]
From the average functionality of the used monomers the reaching of the
gel point can be calculated as a function of reaction progress.
[Koltzenburg: ''Polymere: Synthese, Eigenschaften und Anwendungen'', S. 187 (). This reference is being translated to English as "Polymer Chemistry" by the same authors, to appear in September 2017. Se]
/ref> Side reactions may increase or decrease the functionality.
However, IUPAC definition and the use of the term in organic chemistry differ with respect to the functionality of a double bond.
References
{{Portal, Chemistry
Functional groups