Thiol‐dithioester reaction: An approach to the end‐group removal and end‐functionalization of <scp>RAFT</scp>‐synthesized polymers

Abstract Reversible addition−fragmentation chain transfer (RAFT) polymerization has been one of the most versatile methods in the synthesis of well‐defined polymers. The stability of the thiocarbonylthio chain transfer agents (CTAs) in the polymerization and the removal of CTAs after the polymerization are the two great concerns for the applications of RAFT polymerization. In this research, thiol‐dithioester reaction under the catalysis of triethylamine (TEA) is studied. In a model reaction, thiolate anion has nucleophilic addition reaction with dithioester compound, resulting in the synthesis of a new dithioester and a new thiol compound. The effects of TEA to dithioester molar ratio and reaction time on the yield of the product are investigated. The application of thiol‐dithioester reaction in the removal of end CTAs from polymer chains is studied. 1 H NMR, UV–vis, and size‐exclusion chromatography (SEC) results all demonstrate the effective removal of CTAs and the generation of thiol groups at polymer chain ends. The thiol groups can be further used for the terminal functionalization of polymers. In this research, alkyne‐terminated poly(methyl methacrylate) and FMOC‐ l ‐Cys‐labeled poly(di‐[ethylene glycol] methyl ether methacrylate) are synthesized by TEA‐catalyzed thiol‐ene reaction and thiol‐disulfide reaction, respectively. Thiol‐dithioester reaction provides an effective approach to the removal of CTAs and end functionalization of RAFT synthesized polymers.