In
chemistry, functionality is the presence of
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
s in a
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
. A monofunctional molecule possesses one functional group, a difunctional two, a trifunctional three, and so forth. In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, ...
(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 of chemicals, chemical synthesis, and chemical and physical properties of polymers and macromolecules. The principles and methods used within polymer chemistry are a ...
, the functionality of a
monomer
In chemistry, a monomer ( ; '' mono-'', "one" + ''-mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization.
Classification
...
refers to its number of
polymerizable groups, and affects the formation and the degree of
crosslinking of polymers.
Functionality 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 a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
. 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
Silanization is the covering of a surface with organofunctional alkoxysilane molecules. Mineral components like glass and metal oxide surfaces can all be silanized, because they contain hydroxyl groups which attack and displace the alkoxy groups on ...
for the specific modification of the adhesion of a
surface
A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is ...
)
* the functionalization of nanoparticles 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
Functionality 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
In polymer chemistry, a repeat unit or repeating unit (or mer) is a part of a polymer whose repetition would produce the complete polymer chain (except for the end-groups) by linking the repeat units together successively along the chain, like th ...
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 thermosoft 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 associate ...
). Monomers with a functionality ''f'' ≥ 3 lead to a branching point, which can lead to
cross-linked
In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
polymers (a
thermosetting polymer
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (" curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and ...
). Monofunctional monomers do not exist as such molecules lead to a
chain termination
Chain termination is any chemical reaction that ceases the formation of reactive intermediates in a chain propagation step in the course of a polymerization, effectively bringing it to a halt.
Mechanisms of termination
In polymer chemistry, ...
.
[Eintrag zu ''functionality, f of a monomer''.]
From the average functionality of the used monomers the reaching of the
gel point
In polymer chemistry, the gel point is an abrupt change in the viscosity of a solution containing polymerizable components. At the gel point, a solution undergoes gelation as reflected in a loss in fluidity. Gelation is characteristic of polymeri ...
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.
See also
{{Portal, Chemistry
*Bifunctional
In organic chemistry, when a single organic molecule has two different functional groups, it is called a bifunctional molecule . A bifunctional molecule has the properties of two different types of functional groups, such as an alcohol (), amide ( ...
*Functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the re ...
References
Functional groups