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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 ...
In chain-growth polymerization the propagation step is the addition of a monomer to the growing chain. The word kinetic is added to chain length in order to distinguish the number of reaction steps in the kinetic chain from the number of monomers in the final macromolecule, a quantity named the degree of polymerization. In fact the kinetic ...
Chain-growth includes both initiation and propagation steps (at least), and the propagation of chain-growth polymers proceeds by the addition of monomers to a growing polymer with an active centre. In contrast step-growth polymerization involves only one type of step, and macromolecules can grow by reaction steps between any two molecular ...
The chain length is defined as the average number of times the propagation cycle is repeated, and equals the overall reaction rate divided by the initiation rate. [ 1 ] Some chain reactions have complex rate equations with fractional order or mixed order kinetics.
The growing chain will react with molecular oxygen, producing an oxygen radical, which is much less reactive (Figure 17). This significantly slows down the rate of propagation. Figure 17: Inhibition of polystyrene propagation due to reaction of polymer with molecular oxygen.
Chain termination: radicals combine and the chain carriers are lost. Inhibition: chain carriers are removed by processes other than termination, such as by forming radicals. Even though all these steps can appear in one chain reaction, the minimum necessary ones are Initiation, propagation, and termination.
The reactivity ratio for each propagating chain end is defined as the ratio of the rate constant for addition of a monomer of the species already at the chain end to the rate constant for addition of the other monomer. [2] = =
In the propagation phase, the lipid radical reacts with oxygen (O 2) or a transition metal, forming a peroxyl radical (LOO •). This peroxyl radical continues the chain reaction by reacting with a new unsaturated fatty acid, producing a new lipid radical (L •) and lipid hydroperoxide (LOOH). These primary products can further decompose into ...