Thiocarbonylthio compounds RAFT agents

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... 

Davis et al. [14] in an elegant review on the RAFT technique discuss thiocarbonylthio compounds to mediate the polymerization via a reversible chain-transfer process. This leads to the establishment of equilibrium under which all the propagating chains have approximately the same chain length at the same instant of time. A large class of chain transfer agents that are applied in RAFT polymerizations have the general formula ... 

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

RAFT is a highly versatile method of polymerization that utilizes a chain-transfer agent (CTA) to produce the dormant form of the growing polymer chains. The CTA is commonly a di- or tri-thiocarbonylthio compound that forms a stabilized radical intermediate. Chain equilibration between actively growing and dormant chains leads to uniform rate of chain growth for all polymers, and is linearly related to conversion. Since transition metal catalysts are not required, RAFT has increased compatibility with a wider anay of monomer functionalities than other polymerization methods, hut the... 

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] ... 

Polymerization of VPA was successfully performed by aqueous RAFT/ MADIX polymerization, controlled with O-ethyl xanthate as a transfer agent. Reversible addition-fragmentation chain transfer (RAFT) is a polymerization method which uses a chain transfer agent in the form of a thiocarbonylthio compound such as dithioesters, thiocarbamates, and xanthates having the role to mediate the polymerization via a reversible... 

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-... 

Figure 11.36 A general scheme for RAFT polymerization with thiocarbonylthio compounds as chain transfer agents. When P and Pm are kinetically identical polymers, these need not be distinguished and both may be written as P. (Adapted from Kwak et al., 2004.)...

A RAFT polymerization system consists of initiator, monomer, chain transfer agent, solvent, and temperature. RAFT polymerization can be performed by simply adding a chosen quantity of an appropriate RAFT agent (thiocarbonylthio compounds) to a conventional free radical polymerization. Usually the same monomers, initiators, solvents and temperatures can be used. Because of the low concentration of the RAFT agent in the system, the concentration of the initiator is usually lower than in conventional radical polymerization. Radical initiators such as Azobisisobutyronitrile(AIBN) and 4,4 -Azobis(4-cyanovaleric acid)(ACVA) are widely used as the initiator in RAFT. RAFT polymerization is known for its compatibility with a wide range of monomers compared to other controlled radical polymerizations. These monomers include (meth)acrylates, (meth)... 

A RAFT polymerization system consists of an initiator, monomer, solvent and a chain transfer agent, defined as RAFT agent, which mediates the polymerization via a reversible chain transfer process. RAFT agents are thiocarbonylthio compounds, including dithioesters, dithiocarbamates, trithiocarbonates and xanthates, and characterized by the presence of two different functionalities a Z group, which affects the stability of the C=S bond and controls the effectiveness radicals addition to the growing chain, and a R group, able to initiate new polymeric chains (Fig. 1.10). 

Benzyl thionobenzoate (58) is believed to be ineffective as a transfer agent in MMA polymerization because of an unfavorable partition coefficient. Poly(methyl methacrylate) radical (PMMA ) is a much better radical leaving group than benzyl radical. Analogous benzyl thiocarbonylthio compounds (e.g., benzyl dithiobenzoate or dibenzyl trithiocarbonate) are also ineffective as RAFT agents in MMA polymerization. 

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... 

Some initiators (e.g., dibenzoyl peroxide and potassium per-oxydisulfate) and the derived radicals may oxidize RAFT agents to sulfme or other products. Other initiator radicals may react with the RAFT agent to form a stable thiocarbonylthio compound. It is important that the initiator-derived radical is a good leaving group with respect to the propagating radical. For example, use of an aliphatic diacyl peroxide (e.g., dilauroyl peroxide) will provide a relatively stable RAFT agent with R = primary alkyl. Similarly, azobis(methyl isobutyrate) (AIBMe) is not a suitable choice for RAFT polymerization of MMA. ... 

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