Dormant end group

Trapping agents, such as malonate anions, naphthoxides, and phosphines have been used to determine the concentration of chain carriers in controlled/living and other carbocationic systems [85,249,250]. These strong nucleophiles react with all sufficiently electrophilic species, including not only carbocations but also onium ions and covalent esters. Thus, the discussed measurements can provide only the total concentration of active and dormant end groups. In principle, the kinetics of formation of the product in the trapping experiments could resolve more and less active species but only if they are present at comparable concentrations. As discussed before, carbocations are present in ppm quantities in comparison with dormant species. 

Whether these side reactions are termination or transfer reactions depends on the ability of the anions to re-initiate the polymerization and on the fate of the vinyl ketone formed in Eq. (45). Generally, this vinyl ketone is rapidly incorporated into the chain, and a relatively unreactive dormant end group is produced. The alkoxide from reactions such as Eq. (45) is usually not reactive enough to initiate another chain. 

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