Controlling thiyl radical polymerization via in situ desulfurization

Controlling thiyl radical polymerizations is highly desirable for synthesizing polymers with precisely controlled main-chain structures, yet it remains challenging due to the difficulty of reversibly controlling propagating thiyl radicals with existing methods. Here, we present a new strategy in which the propagating thiyl radical undergoes desulfurization with trivalent phosphorus, generating a stabilized carbon radical for reversible control. This approach enables the radical ring-opening polymerization of macrocyclic allylic sulfides to be effectively regulated by reversible addition–fragmentation chain transfer (RAFT) agents, resulting in polymers with well-defined architectures, which was exemplified by the successful incorporation of sequence-defined segments into the polymer backbone, along with diblock copolymerization of macrocyclic allylic sulfides. This work will further advance thiyl radical polymerizations toward polymers with controlled main-chain functionalities.