Reversible addition-fragmentation degenerative transfer process

The other CRP process to be disclosed in the 1990 s relies on degenerative transfer of an atom or group and is best exemplified by the reversible addition-fragmentation transfer (RAFT) process that employs dithioesters as chain-transfer agents which was introduced in 1998. (17-19)... 

Currently three systems seem to be the most efficient processes for conducting a CRP nitroxide mediated polymerization (NMP) (eq. 1 in Fig. 5), atom transfer radical polymerization (ATRP) (eq. 2 in Fig. 5) and degenerative transfer systems (eq. 3 in Fig. 5) such as reversible addition-fragmentation transfer (RAFT) or iodine degenerative transfer (IDT) processes (88-90). The key feature of all CRPs is the dynamic equilibration between active radicals and various types of dormant species. 

Radical polymerizations that involve a reversible chain transfer step for chain equilibration and that displayed the characteristics of living polymerizations were first reported in 1995. ° The mechanism of the reversible chain transfer step may involve homolytic substitution (Scheme 73) or addition-fragmentation (RAFT) (Scheme 74). An essential feature is that the product of chain transfer is also a chain transfer agent with similar activity to the precursor transfer agent. The process has also been termed degenerate or degenerative chain transfer... 

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