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 ...
, chain propagation (sometimes just referred to as propagation) is a process in which a
reactive intermediate
In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these comp ...
is continuously regenerated during the course of a
chemical chain reaction. For example, in the
chlorination of
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
, there is a two-step propagation cycle involving as chain carriers a chlorine atom and a
methyl radicalChain reaction
IUPAC Gold Book which are regenerated alternately:
:
:
The two steps add to give the equation for the overall chain reaction:
:
Polymerization
In a chain-growth polymerization
Chain-growth polymerization (American English, AE) or chain-growth polymerisation (British English, BE) is a polymerization technique where monomer molecules add onto the active site on a growing polymer chain one at a time. There are a limited n ...
reaction, the reactive end-group
End groups are an important aspect of polymer synthesis and characterization. In polymer chemistry, they are Functional group, functional groups that are at the very ends of a macromolecule or oligomer (IUPAC). In polymer synthesis, like condens ...
s of a polymer chain react in each propagation step with a new 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 ...
molecule transferring the reactive group to the last unit. Here the chain carrier is the polymer molecule with a reactive end-group, and at each step it is regenerated with the addition of one monomer unit M:
External links
* IUPAC Gold Book
The International Union of Pure and Applied Chemistry (IUPAC) publishes many books which contain its complete list of definitions. The definitions are divided initially into seven IUPAC Colour Books: Gold, Green, Blue, Purple, Orange, White, and R ...
definition
chain-propagating reaction
References
{{polymer-stub
Chemical reactions
Polymer chemistry