Chain propagation

IUPAC definition

(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 kp.

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 which are regenerated alternately:

·Cl + CH4 → HCl + ·CH3
·CH3 + Cl2 → CH3Cl + ·Cl

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

CH4 + Cl2 → CH3Cl + HCl
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