Living radical polymerization activation-deactivation processes

Mechanistically, LRP is distinguished from conventional radical polymerization by the reversible activation process. P-X is activated to the polymer radical P by thermal, photochemical, or chemical stimuli. In the presence of monomer M, P will propagate until it is deactivated back to P-X. For practically important systems, it usually holds that [P]/[P-X] < 10 , meaning that a living chain spends most of its polymerization time in the dormant state (here, living chain denotes the sum of the dormant and active chains). The activation-deactivation cycles will be repeated enough times to allow all... 

In order to reduce the contribution of termination processes (Scheme 2.19), controlled/living radical methods establish a fast equilibrium between dormant and active chain ends. Essentially, this equilibrium decreases the relative proportion of propagating radicals and allows them to reversibly deactivate rather than permanently terminate. The radical chain end concentration for CRPs (10 -10" M) is also much less than for ionic polymerizations (10 -10 M). 

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