RAFT Polymerization: Mechanistic Considerations

Reversible addition–fragmentation chain transfer (RAFT) polymerization is a powerful methodology that enables synthesis of polymers with complex molecular architecture and can use a wide variety of functional monomers. The technique requires the use of a chain transfer agent (i.e. a RAFT agent) that reacts via a reversible addition–fragmentation mechanism, giving rise to a polymer that itself is a chain transfer agent. In this chapter, the mechanism of RAFT polymerization is described in detail, including how the structure of the RAFT agent affects both its suitability for a particular monomer and the associated kinetics of the polymerization. Various mechanistic explanations for the kinetic effects are presented. Additionally, potential side reactions are considered, including the side fragmentation of xanthates and hydrolysis of dithioesters. The ability to use mechanistic insights into design RAFT agents with broad applicability, and to establish the relative importance of RAFT and iniferter mechanisms, is discussed. Finally, emerging areas for which mechanistic understanding will provide further insights, such as RAFT polymerization under visible light, are described.