Initiator‐Activation Strategy‐Enabled Organocatalyzed Reversible‐Deactivation Radical Polymerization Driven by Light

Abstract Organocatalyzed reversible‐deactivation radical polymerizations (RDRPs) are attractive for many applications. Here, we developed photoredox‐mediated RDRP by activating (hetero)aryl sulfonyl chloride (ArSO 2 Cl) initiators with pyridines and designing a novel bis(phenothiazine)arene catalyst. The in situ formed sulfonyl pyridinium intermediates effectively promote controlled chain‐growth from ArSO 2 Cl, enabling access to various well‐defined polymers with high initiation efficiencies and controlled dispersities under mild conditions. This versatile method allows “ON/OFF” temporal control, chain‐extension, facile synthesis of different polymer brushes via organocatalyzed grafting reactions from linear chains. Time‐resolved fluorescence decay studies and calculations support the reaction mechanism. This work provides a transition‐metal‐free RDRP to tailor polymers with readily available aromatic initiators, and will promote the design of polymerization leveraged from photoredox catalysis.