Reversible addition−fragmentation chain-transfer polymerization

Reversible addition-fragmentation chain transfer or RAFT polymerization is one of several kinds of reversible-deactivation radical polymerization. It makes use of a chain transfer agent in the form of a thiocarbonylthio compound (or similar, from here on referred to as a RAFT agent, see Figure 1) to afford control over the generated molecular weight and polydispersity during a free-radical polymerization. Discovered at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) of Australia in 1998, RAFT polymerization is one of several living or controlled radical polymerization techniques, others being atom transfer radical polymerization (ATRP) and nitroxide-mediated polymerization (NMP), etc. RAFT polymerization uses thiocarbonylthio compounds, such as dithioesters, thiocarbamates, and xanthates, to mediate the polymerization via a reversible chain-transfer process. As with other controlled radical polymerization techniques, RAFT polymerizations can be performed with conditions to favor low dispersity (molecular weight distribution) and a pre-chosen molecular weight. RAFT polymerization can be used to design polymers of complex architectures, such as linear block copolymers, comb-like, star, brush polymers, dendrimers and cross-linked networks.Degenerate-transfer radical polymerization in which chain activation and chain deactivation involve a degenerative chain-transfer process which occurs by a two-step addition-fragmentation mechanism.Note 1: Examples of RAFT agents include certain dithioesters, trithiocarbonates, xanthates(dithiocarbonates), and dithiocarbamates. Reversible addition-fragmentation chain transfer or RAFT polymerization is one of several kinds of reversible-deactivation radical polymerization. It makes use of a chain transfer agent in the form of a thiocarbonylthio compound (or similar, from here on referred to as a RAFT agent, see Figure 1) to afford control over the generated molecular weight and polydispersity during a free-radical polymerization. Discovered at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) of Australia in 1998, RAFT polymerization is one of several living or controlled radical polymerization techniques, others being atom transfer radical polymerization (ATRP) and nitroxide-mediated polymerization (NMP), etc. RAFT polymerization uses thiocarbonylthio compounds, such as dithioesters, thiocarbamates, and xanthates, to mediate the polymerization via a reversible chain-transfer process. As with other controlled radical polymerization techniques, RAFT polymerizations can be performed with conditions to favor low dispersity (molecular weight distribution) and a pre-chosen molecular weight. RAFT polymerization can be used to design polymers of complex architectures, such as linear block copolymers, comb-like, star, brush polymers, dendrimers and cross-linked networks. The addition-fragmentation chain transfer process was first reported in the early 1970s. However, the technique was irreversible, so the transfer reagents could not be used to control radical polymerization at this time. For the first few years addition-fragmentation chain transfer was used to help synthesize end-functionalized polymers. Scientists began to realize the potential of RAFT in controlled radical polymerization in the 1980s. Macromonomers were known as reversible chain transfer agents during this time, but had limited applications on controlled radical polymerization. In 1995, a key step in the 'degenerate' reversible chain transfer step for chain equilibration was brought to attention. The essential feature is that the product of chain transfer is also a chain transfer agent with similar activity to the precursor transfer agent. RAFT polymerization today is mainly carried out by thiocarbonylthio chain transfer agents. It was first reported by Rizzardo et al. in 1998. RAFT is one of the most versatile methods of controlled radical polymerization because it is tolerant of a very wide range of functionality in the monomer and solvent, including aqueous solutions. RAFT polymerization has also been effectively carried out over a wide temperature range.