Synthesis of RAFT Agents

Scheme 31.25 (a) Synthesis of RAFT agent 73 built from an NHC (b) Polymerization of styrene, as catalyzed by 73. Mes ... 

Radical-induced decomposition of a bis (thioacyl) disulfide (e.g. Scheme 3).[i .i3-i61 is probably the most used method for the synthesis of RAFT agents requiring tertiary R groups. It is also possible to use this chemistry to generate a RAFT agent in situ during polymerization. ... 

References cited in this column provide a synthesis of RAFT agent. The letter indicates the method used (see Section 3.07.3.2.1). References cited provide details of polymerization of the monomers indicated. 

Only a limited selection of RAFT agents is commercially available. Many procedures for the synthesis of RAFT agent have been described and the major ones are summarized in Scheme 6.17 which is taken from our recent review. The most commonly used involves the reaction of a carbodithioate salt with an alkylating agent. However, other processes have important niche applications. These include various thioacylation reactions, the thiation of the corresponding... 

Also, Kerep and Ritter reported a radical chain transfer agent as a dual initiator, FRP-1 [45]. The first step builds on the fact that hydroxyl groups are much better nucleophiles in enzymatic ROP than thiols. Due to the chemoselectivity of the enzyme, PCLs with predominantly thiol endgroups were obtained, which were subsequently used as macroinitiator for styrene. The authors report that the reaction yield can be further increased by microwave irradiation. Although thiols provide less control over the radical polymerization than RAFT agents, the subsequent radical polymerization successfully leads to the synthesis of PCL-Z -PS. 

CRP is a powerful tool for the synthesis of both polymers with narrow molecular weight distribution and of block copolymers. In aqueous systems, besides ATRP, the RAFT method in particular has been used successfully. A mrmber of uncharged, anionic, cationic, and zwitterionic monomers could be polymerized and several amphiphilic block copolymers were prepared from these monomers [150,153]. The success of a RAFT polymerization depends mainly on the chain transfer agent (CTA) involved. A key question is the hydrolytic stability of the terminal thiocarbonyl functionaHty of the growing polymers. Here, remarkable progress could be achieved by the synthesis of several new dithiobenzoates [150-152]. 

---