Reversible addition-fragmentation chain transfer precursors

In this review, the term macromer is used to describe oligomer or polymer precursors that undergo reversible association to form supramolecular polymers or networks. Macromer synthesis, although a crucial aspect of supramolecular science, is also out of the scope of this review. Several comprehensive reviews of the synthesis of H-bonding polymers are available [10, 11,42] and primarily describe the application of controlled radical polymerization techniques, including atom-transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP). For synthesis of telechelic polymers, avoiding monofunctional impurities that can act as chain stoppers is crucially important [43],... 

Alternatively, Whittaker et al. utilized the reversible oxidation/reduction of a thiol-terminated linear polymer as a homocoupling reaction to access macrocycles that could be reversibly cyclized and cleaved (Scheme 12.5) [29]. The linear precursors were prepared using reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene from a bifunctional initiator (16). The desired polystyrene with thiol end groups could be isolated in near-quantitative yields by aminolysis of the polymer with terminal dithioester groups (17). The linear dithiols... 

In 2013, a combined effort by groups from Germany and France saw the application of tetrazole precursors in the photoinduced tetr2izole-ene coupling process leading to nitrile-butadiene rubber with molar masses up to 48 kDal [95]. The reversible addition-fragmentation chain transfer (RAFT) procedure was employed, using a tetrazole-functionalized trithiocarbonate. 

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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