What is the final stage of addition polymerization where a chain stopper is used called?

The final stage of addition polymerization where a chain stopper is used is known as termination. This process occurs when the growth of the polymer chain is halted, typically through the reaction of a chain-terminating agent, which effectively "stops" the polymerization process. During termination, the active sites of growing polymer chains react with these agents, leading to the formation of stable polymer products without further growth of the chain.

Initiation refers to the stage where the polymerization process begins, often involving the generation of reactive species that can start the addition of monomers. Propagation is the stage where the polymer chain grows as successive monomer units are added, whereas completion is not a standard term typically associated with the specific stages of addition polymerization. Understanding the role of termination in polymer chemistry is crucial because it ultimately defines the final structure and molecular weight of the resulting polymer.