Selective Electrochemical End-Group Removal Enhances Polymer Thermal Stability

Here we introduce an electrochemical strategy for the selective and quantitative removal of thiocarbonylthio end groups from polymers prepared by reversible addition-fragmentation chain transfer (RAFT) or photoiniferter polymerization. Our results indicate that applying a cathodic potential in an undivided cell promotes reductive cleavage of the thiocarbonylthio moiety, generating terminal polymer radicals that are efficiently capped with hydrogen atoms in the presence of benign donors. This transformation proceeds cleanly across diverse polymer backbones and end-group chemistries, including trithiocarbonates and dithiobenzoates, without chain coupling or degradation. Moreover, the applied potential can be tuned to enable chemoselective end-group removal in mixed-polymer systems, a level of control inaccessible by thermal, photochemical, or nucleophilic strategies. Beyond delivering colorless and optically transparent materials, electrochemical end-group removal significantly enhances polymer stability. Poly(methyl methacrylate) subjected to electrochemical end-group removal exhibited a T₉₅ of 342 °C, exceeding the stabilities of analogous polymers with end groups removed by aminolysis (T₉₅ = 260 °C) or radical-based methods (T₉₅ = 299 °C). These findings demonstrate redox-directed post-polymerization modification as a tool for designing robust, transparent, and thermally stable macromolecules and establish electrochemistry as a platform strategy in polymer synthesis and processing.