Design and Synthesis of a New Indazole-Decorated RAFT Agent for Highly Efficient PET-RAFT Polymerization

While enabling precise control and well-defined molecular weights in polymer synthesis, photocatalyzed reversible deactivation radical polymerization (photo-RDRP) suffers from slow kinetics, limiting its broader application in advanced manufacturing. Despite a decade of research on photocatalyst design, progress in significantly improving the kinetics of photo-RDRP remains insufficient. In contrast, the role of the initiator in photo-RDRP is often overlooked, especially in photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, where the RAFT agent serves as both the initiator and chain transfer agent. In this work, we first designed and synthesized a new RAFT agent with an indazole Z group (InZ) for highly efficient PET-RAFT polymerization under irradiation. This strongly electron-donating Z group accelerates initiation by facilitating pi* -> sigma* charge transfer in PET-RAFT systems. Compared to the commonly used trithiocarbonates in PET-RAFT polymerization, utilization of InZ improved polymerization rates significantly by 2.7-fold. Additionally, we discovered a new efficient photocatalyst (PC) in PET-RAFT polymerization, i.e., zinc 5,10,15,20-tetra(naphthalen-2-yl)porphyrin (ZnTNP), through experimental screening of various zinc porphyrin derivates. This ZnTNP/InZ system exhibits precise temporal and molecular weight control in the course of polymerization, being compatible with a broad range of acrylates and acrylamides and exhibiting good oxygen tolerance. Importantly, InZ may inspire further development of high-performance RAFT agents for PET-RAFT polymerization.