A reaction of polyaddition or polymerization in chain, is a reaction leading to the formation of by successive additions of monomers on an end activates .
It is the nature of the active end which makes it possible to name the method of polymerization by reaction of polyaddition. For example, if this active end is a radical, one speaks about . One can also bring into play ionic ends (anion or cation), or many connections Carbon-Metal.
When this polymerization implies monomers, , reaction of polymerization in chain () will synthesize a molecule ofADN following the reaction of polyaddition.