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This paper presents a review of living radical polymerization achieved with thiocarbonylthio compounds [ZC( S)SR] by a mechanism of reversible addition-fragmentation chain transfer (RAFT). Since we first introduced the technique in 1998, the number of papers and patents on the RAFT process has increased exponentially as the technique has proved to be one of the most versatile for the provision of polymers of well defined architecture. The factors influencing the effectiveness of RAFT agents and outcome of RAFT polymerization are detailed. With this insight, guidelines are presented on how to conduct RAFT and choose RAFT agents to achieve particular structures. A survey is provided of the current scope and applications of the RAFT process in the synthesis of well defined homo-, gradient, diblock, triblock, and star polymers, as well as more complex architectures including microgels and polymer brushes.

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This paper provides a third update to the review of reversible deactivation radical polymerization (RDRP) achieved with thiocarbonylthio compounds (ZC(¼S)SR) by a mechanism of reversible addition-fragmentation chain transfer ( Chem. 2009Chem. , 62, 1402. This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymerization which include reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.

Radical polymerization with reversible addition−fragmentation chain transfer (RAFT polymerization) can be used to synthesize a wide range of polymers of controlled architecture and narrow molecular weight distribution. The polymerizations use addition−fragmentation chain transfer agents (RAFT agents) that possess high transfer coefficients in free radical polymerization and confer living character on the polymerization. This paper explores the effect of the substituents R of dithiobenzoate RAFT agents [SC(Ph)S−R] on the outcome of polymerizations of styrene, methyl methacrylate (MMA) and butyl (BA) or methyl acrylate (MA). In MMA polymerization at 60 °C, effectiveness depends strongly on R decreasing in the order where R is:  −C(Alkyl)2CN ∼ −C(Me)2Ar > −C(Me)2C(O)O(alkyl) > −C(Me)2C(O)NH(alkyl) > −C(Me)2CH2C(Me)3 ≥ −C(Me)HPh > −C(Me)3 ∼ −CH2Ph. Of these, only the compounds with R = −C(Me)2Ph and −C(Me)2CN provided polymers with substantially narrowed polydispersities in batch polymerization and gave molecular weight control of the form expected for a living polymerization. These compounds have high transfer coefficients in MMA polymerization (transfer coefficient >20 for 0.003 M RAFT agent in bulk MMA). Reagents with R = −C(Me)2C(O)O(alkyl), C(Me)2C(O)NH(alkyl), −C(Me)2CH2C(Me)3, −C(Me)HPh, −C(Me)3, and −CH2Ph appear relatively ineffective in MMA polymerization because they have much lower transfer coefficients (ca. 1.7, 0.7, 0.4, 0.15, 0.03, and 0.03 respectively). In polymerizations of styrene or acrylates at 60 °C, transfer coefficients of RAFT agents are several orders of magnitude higher and all compounds in the above series yield narrow polydispersity polymers. The transfer coefficients of benzyl dithiobenzoate in styrene and methyl acrylate polymerization at 60 °C are ca. 50 (0.0093 M RAFT agent in bulk monomer) and 105 (with 0.003−0.006 M RAFT agent in 4.43 M monomer), respectively. The rate constant for addition to the thiocarbonyl group does not depend strongly on R. Differences in activity depend on the properties of R and the propagating chain as free radical leaving groups and on the partitioning of R• between adding to monomer (to reinitiate) and adding to polymeric RAFT agent. When the reaction of R• with the polymeric RAFT agent to reform the initial RAFT agent is significant, the transfer coefficient may reduce with concentration of RAFT agent and with conversion. In these circumstances, the activity of RAFT agents is best characterized by two transfer constants associated with the forward and reverse reactions. Steric factors, polar factors, and the stability of R• all appear to play an important role in determining the transfer coefficient and the effectiveness of RAFT agents.

This paper provides a first update to the review of living radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of Reversible Addition-Fragmentation chain Transfer (RAFT) published in June 2005. The time since that publication has witnessed an increased rate of publication on the topic with the appearance of well over 200 papers covering various aspects of RAFT polymerization ranging over reagent synthesis and properties, kinetics, and mechanism of polymerization, novel polymer syntheses, and diverse applications.

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