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

Abstract

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 π* → σ* 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.

Pushing the Limit of Photo-Controlled Polymerization: Hyperchromic and Bathochromic Effects

“…In the absence of light, no side reactions occur (Figure 3G,J). Remarkably, ZnTPTBP also exhibits excellent resistance to oxygen, like the cases of ZnTPP and ZnTNP with InZ as the RAFT agent [41]. Despite the presence of oxygen leading to a decrease in the polymerization rate (k app p = 0.128 min -1 ) and a prolonged induction period, ZnTPTBP exhibits a polymerization rate that still exceeds that of ZnTPP-catalyzed PET-RAFT polymerization (k app p = 0.120 min -1 ) (Table 2).…”

“…The synthetic methods of ZnTNP and ZnTPTBP were based on our recent work [41]. Taking ZnTPTBP as an example, 20.0 mg (24.5 µmol) of TPTBP, 6.7 mg (36.8 µmol) of anhydrous zinc acetate, and 15.0 mL of DMF were added to a glass vial with a stir bar.…”

“…The synthesis of InZ mainly includes two pathways (Figure S10) [41][42][43], with one of them being via bis(3-methyl-1H-indazole-1-carbothioic)disulfide. 3-Methyl-1H-indazole (2.00 g, 15.1 mmol) was added to a solution of potassium hydroxide (0.85 g, 15.1 mmol) in tetrahydrofuran (100.0 mL) at 0-5 • C. The mixture was stirred at 0-5 • C for 15 min.…”