Discovery of the RAFT/MADIX Process: Mechanistic Insights and Polymer Chemistry Implications

Abstract

This Perspective outlines the observations leading to the discovery of the degenerative exchange of xanthates and related thiocarbonylthio derivatives. It compares this process with the older Kharasch reaction and discusses the key ability to reversibly store active radicals in a nonreactive form. Implications for the synthesis of polymers beyond the RAFT/MADIX technology are discussed, namely, the modification of industrial polymers, the synthesis of novel monomers, oligomers, and surfactants from biosourced feedstocks, especially through an alliance with the powerful metathesis reaction. The synthesis of trialkoxysilane cross-linkers for sol–gels and the use of boronates for the construction of well-defined sequences by controlled insertion of single monomers are discussed briefly.

Playing construction with the monomer toy box for the synthesis of multi‐stimuli responsive copolymers by reversible deactivation radical polymerization protocols

“…Polymerization control in the RAFT process is based on the degenerate addition‐fragmentation equilibria involving a CTA (dithioester, xanthate, trithiocarbonate, or dithiocarbamate) and the chain‐propagating radical 80–82 . Recent literature confirms the significant impact of RAFT in the field of MSR polymers with a wealth of diverse monomers processed.…”

The xanthate route to lactams

“…Indeed, the broad versatility of the reversible In the case of dithiocarbamates, it is important to increase the reactivity of the thiocarbonyl by placing an electron-withdrawing moiety on the nitrogen (even just a phenyl group) or an acyl group on the sulfur. 20 Furthermore, S-acyl dithiocarbonyl derivatives, such as S-acyl xanthates and S-acyl dithiocarbamates, are yellow in color and the radical chain process can be conveniently triggered by irradiation with visible light. 22 The examples collected in scheme 4 illustrate the synthesis of various b-lactams 26a-j, including bicyclic and spirocyclic derivatives, starting from S-acyl dithiocarbamates 25 derived from the appropriate allylic amines.…”

A Practical Route to Cyclobutanols and Fluorocyclobutanes

“…Our foray into this area arose as part of our larger study of a novel radical chemistry of xanthates and related thiocarbonylthio derivatives and their application to solving diverse synthetic problems [22–25] . Extension of this technology to the case of cyclobutanols hinges on the accessibility of xanthate 7 and its stability and behavior under typical reaction conditions.…”