Recent progress in switchable RAFT agents: Design, synthesis and application

Abstract In the past two decades, reversible addition-fragmentation chain transfer (RAFT) process has developed into one of the most versatile methods of producing polymers with “living” chain end groups in radical polymerization. The monomers employed in RAFT polymerization are classified into two broad classes based on their reactivities. That is the more activated monomers (MAMs) and the less activated monomers (LAMs). Reports have shown that RAFT agents such as dithioesters (Z = aryl, alkyl) or trithiocarbonates (Z = alkylthio) are suitable for controlling polymerization of MAMs but does not favour the polymerization of LAMs. Similarly, LAMs-favouring RAFT agents (such as Z = N-alkyl-N-aryl dithiocarbamates and O-alkyl xanthates) are less effective with MAMs. In 2009 a new class of stimuli-responsive RAFT agents referred to as universal or “switchable” RAFT agents were reported. This class of agents can be switched in situ under acidic/basic conditions to provide good control over polymerization of both MAMs and LAMs thus giving access to poly(MAM)-block-poly(LAM) copolymers. In this review we discuss the development of the “switchable” RAFT agents and their application since 2009 to 2020.