LRP by Degenerative Transfer

As mentioned above, in both NMP and ATRP the exchange between the active and the dormant states is based on a reversible (although different) termination mechanism. Therefore, the exchange directly affects the radical concentration. In LRP by degenerative transfer, instead, this exchange is carried out by direct transfer of the w-end group between an active and a dormant chain. When an iodine atom is used as end group, the reaction can be expressed as follows  

Therefore, the main difference from the previous two systems is that this living mechanism does not form new radicals and a conventional initiator is needed to start and sustain the reaction. The initial amount of this species has to be properly selected. In fact, since the living reaction (3) does not affect the radical concentration, the final concentration of the chains terminated by bimolecular combination will be half of the initial concentration of the initiator. Therefore, the initial concentration of the species carrying the iodine group (in the following simply called the transfer agent ) determines the final DP of the polymer provided that the initiator concentration is small compared with that of the transfer agent. 

Only a few papers have appeared dealing with LRP by DT [8], and the applications are almost completely limited to the homopolymerization of styrene. In this case, it was possible to obtain good control of the final CLD, with polydispersity values as low as 1.3-1.4. Better performances are difficult with styrene, mainly because of the limited transfer activity of the iodine atoms. This is the main reason for the very poor results obtained when applying this process to the polymerization of acrylates (e.g. n-butyl acrylate) and for the complete lack of control reported for other monomers [8]. 

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