Progress and Perspectives Beyond Traditional RAFT Polymerization

Abstract

The development of advanced materials based on well-defined polymeric architectures is proving to be a highly prosperous research direction across both industry and academia. Controlled radical polymerization techniques are receiving unprecedented attention, with reversible-deactivation chain growth procedures now routinely leveraged to prepare exquisitely precise polymer products. Reversible addition-fragmentation chain transfer (RAFT) polymerization is a powerful protocol within this domain, where the unique chemistry of thiocarbonylthio (TCT) compounds can be harnessed to control radical chain growth of vinyl polymers. With the intense recent focus on RAFT, new strategies for initiation and external control have emerged that are paving the way for preparing well-defined polymers for demanding applications. In this work, the cutting-edge innovations in RAFT that are opening up this technique to a broader suite of materials researchers are explored. Emerging strategies for activating TCTs are surveyed, which are providing access into traditionally challenging environments for reversible-deactivation radical polymerization. The latest advances and future perspectives in applying RAFT-derived polymers are also shared, with the goal to convey the rich potential of RAFT for an ever-expanding range of high-performance applications.

Keywords: controlled/living polymerization; photochemistry; polymer structures; reversible addition‐fragmentation chain transfer (RAFT); spatiotemporal regulation.

Figure 1

Emerging methods for activating RAFT polymerization. The traditional route of RAFT activation by adding exogenous, thermal‐ or redox‐labile reagents is being supplanted by novel activation strategies that can increase livingness and provide scope for external regulation.

Figure 2

RAFT is now possible in reaction settings where traditional radical polymerization has seldom been applied. Such advances pave the way for RAFT to make impact in new and emerging applications, including aerobic and biological settings and in continuous flow processes.

Figure 3

Innovative new applications of RAFT polymerization. a) Polymeric micelle, rod and vesicle nanoparticle morphologies synthesized via polymerization‐induced self‐assembly (PISA).^{[ 117 ]} Adapted with permission. ¹¹⁸ , ¹¹⁹ Copyright 2011, American Chemical Society; and Copyright 2013, American Chemical Society, respectively. b) Light‐induced RAFT single‐unit monomer insertion (SUMI) technique for the preparation of sequence‐controlled oligomers.^{[ 120 ]} c) Enzyme/(nanozyme) facilitated RAFT polymerization to prepare UHMW polymers in air^{[ 87 ]} also achieved efficiently using photoiniferter RAFT.^{[ 121 ]} d) Autonomous self‐optimizing flow reactors afford online optimization of RAFT.^{[ 122 ]} e) Combinatorial discovery of antimicrobial copolymers via PET‐RAFT polymerization. f) The use of PET‐RAFT to develop visible‐light‐mediated photocuring techniques for application in 3D printing.^{[ 123 ]}