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
In chemistry, bifunctionality or difunctionality is the presence of two functional groups in a molecule. A bifunctional species has the properties of each of the two types of functional groups, such as an alcohol (), amide (), aldehyde (), nitrile ...
(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 Cross-linking may refer to
*Cross-link
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 ca ...
of
polymers
A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, b ...
.
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
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...
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 attachment of an organosilyl group to some chemical species. Almost always, silanization is the conversion of a silanol-terminated surface to a alkylsiloxy-terminated surface. This conversion confers hydrophobicity to a previ ...
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
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
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
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 the beads of a necklace ...
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
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
In polymer chemistry, 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 ...
.
[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. After the monomer/polymer solution ha ...
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