Chain propagation

{{Short description|Propagation of a chemical chain reaction by continuously regenerating a reactive species}}

{{Quote box

|title =IUPAC definition

|quote = (in a chain polymerization) Chemical reaction between a chain carrier and a monomer that results in the growth of a polymer chain and the regeneration of at least one chain carrier.

Note 1: The recommended symbol for the rate constant for chain propagation in a homopolymerization is {{math|k_p}}.

|source = [https://www.iupac.org/publications/pac/pdf/2008/pdf/8010x2163.pdf Penczek S.; Moad, G. Pure Appl. Chem., 2008, 80(10), 2163-2193]

|align = right

}}

In chemistry, chain propagation (sometimes just referred to as propagation) is a process in which a reactive intermediate is continuously regenerated during the course of a chemical chain reaction. For example, in the chlorination of methane, there is a two-step propagation cycle involving as chain carriers a chlorine atom and a methyl radical[http://goldbook.iupac.org/C00960.html Chain reaction] IUPAC Gold Book which are regenerated alternately:

:{{chem2|*Cl + CH4 -> HCl + *CH3}}

:{{chem2|*CH3 + Cl2 -> CH3Cl + *Cl}}

The two steps add to give the equation for the overall chain reaction:

:{{chem2|CH4 + Cl2 -> CH3Cl + HCl}}