Thiocarbonylthio RAFT agents

Living radical polymerization using thiocarbonylthio RAFT agents (including dithioesters, trithiocarbonates and xanthates) was first described in a patent published in 1998.40S The first paper describing the process also appeared in 1998.1R Other patents and papers soon followed. Papers on this method, along with NMP and ATRP, now dominate the literature on radical polymerization. 

Many thiocarbonylthio RAFT agents (164) have now been described. Transfer constants are strongly dependent on the Z and R substituents. For an efficient RAFT polymerization (refer Scheme 9.38 and Figure 9.3) ... 

A wide variety of thiocarbonylthio RAFT agents (ZC(=S)SR, 1) have now been reported. A broad summary of these and the factors which influence choice of RAFT agent for a particular polymerization is presented in recent reviews.The effectiveness of the RAFT agent depends on the monomer being polymerized and is determined by the properties of the free radical leaving group R and the group Z which can be chosen to activate or deactivate the thiocarbonyl double bond of the... 

Thiocarbonylthio RAFT agents include certain dithioesters, trithiocarbonates, xanthates, dithiocarbamates, and other compounds. Figure 5 provides general guidance on how to select the appropriate thiocarbonylthio RAFT agent for a particular monomer. It should be dear that with just two RAFT agents it should be possible to exert effective control over the vast... 

RAFT Polymerization with Thiocarbonylthio RAFT Agents... 

The thiocarbonylthio group can be transformed post-polymerization in a variety of ways to produce end-functional polymers or it can be removed. The presence of the thiocarbonylthio groups also means that the polymers synthesized by RAFT polymerization are usually colored and they possess a labile end group that may decompose to produce sometimes odorous byproducts. Even though the color and other issues may be modified by appropriate selection of the initial RAFT agent, these issues have provided further incentive to develop effective methods for treatment of RAFT-synthesized polymer to transform the thiocarbonylthio groups post-polymerization. 

Polymers with primary or secondary amine functionality cannot be prepared directly by RAFT polymerization these groups undergo facile reaction with thiocarbonylthio compounds. Such polymers can be prepared indirectly using RAFT agents with latent amine functionality, such as the phthalimido group in... 

The first well established RAFT polymerization using thiocarbonylthio compounds was reported by CSIRO in 1998 [51]. Subsequently, another group reported a similar mechanism using xanthate RAFT agent they named this technique macromolecular... 

Dithiocarbamate Tritbiocarbonates Scheme 4. Thiocarbonylthio compounds explored as RAFT agents for VAc... 

The effectiveness RAFT agents were investigated by Moad and coworkers [277]. These RAFT agents, such as thiocarbonylthio compounds, depend in effectiveness on the nature of the group, Z and R (shown below) that modify the reactivity of the thiocarbonyl group toward free radical addition. R is the free radical leaving group [277] ... 

Control of radical poljmerization with the addition of thiocarbonylthio compounds that serve as reversible addition fragmentation chain transfer (RAFT) agents was first reported in 1998. Since that time much research carried out in these laboratories and elsewhere has demonstrated that RAFT polymerization is an extremely versatile process.f It can be applied to form narrow polydispersity poljmers or copolymers from most monomers amenable to radical poljmerization. It is possible to take RAFT poljmerizations to high conversion and achieve commercially acceptable polymerization rates. Polymerizations can be successfully carried out in heterogeneous media (emulsion, miniemulsion, suspen-... 

In this paper we add to the picture by describing how to choose RAFT agents for controlling methyl methacrylate polymerization, how to remove the thiocarbonylthio functionality from RAFT-synthesized polymers and how to use RAFT polymerization to achieve simultaneous control over molecular weight, molecular weight distribution and tacticity. 

A key feature of the RAFT process is that the thiocarbonylthio groups, present in the initial RAFT agent, are retained in the... 

A whole variety of thiocarbonylthio compoimds have been S5mthesized and used in RAFT polymerization. The initial work was focused to some extent on the use of dithioesters. More recently the range of RAFT agents is expanded to trithiocarbonates, dithiocarbamates, and xanthates. 

It is evident from the above mechanism that the thiocarbonylthio group of the original RAFT agent is retained in the polymeric product (via P -X and Pm-X). This retention of the thiocarbo-... 

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