Reversible addition−fragmentation chain-transfer polymerization

The so-called RAFT or Reversible addition-fragmentation chain transfer ( reversible addition-fragmentation chain transfer ) - polymerization is a special form of controlled free radical polymerization.

RAFT was based first described in 1998 by the Working Group to Ezio Rizzardo ( CSIRO ) on the work by Sam Zard (Paris). Primarily, it involves an independent method for the controlled synthesis of polymers with well-defined molar mass or degree of polymerization, low polydispersity and known final functionality. There is a controlled process in RAFT, complex molecular architectures such as block, star or comb polymers are also accessible. Control of the reaction is achieved by reversible chain transfer reactions. It adds a growing radical chain to the so-called RAFT -agent, to produce an intermediate radical is formed. Due to the structure of the RAFT agents this intermediate has the potential to fragment into different directions, which in turn a RAFT -agent as well as an available for propagation radical is re-formed (which, however, does not explicitly have to correspond to the original radical chain ). In this way the Propagationswahrscheinlichkeit is uniformly distributed over all of the chains. The average chain length of the polymer formed is proportional to the RAFT agent concentration and the reaction conversion. Typical classes of compounds for RAFT agents are dithioester, dithiocarbamates, and xanthates trithiocarbonates.

RAFT is one next to the so-called atom transfer radical polymerization ( ATRP) and nitroxide - mediated polymerization (NMP ) of the best known and most important representatives of the controlled free radical polymerization. Its widespread distribution RAFT owes its compatibility with a large number of monomers and the relatively mild conditions under which the reactions can be carried out. Unlike ATRP and RAFT polymerization caused NMP (albeit with exceptions prominent ) no retardation of the reaction rate, which allows faster and thus cheaper synthesis.