Organic Photocatalyst for ppm-Level Visible-Light-Driven Reversible Addition–Fragmentation Chain-Transfer (RAFT) Polymerization with Excellent Oxygen Tolerance

Abstract

A highly efficient organic photocatalyst (OPC) for photoinduced electron/energy-transfer reversible addition–fragmentation chain-transfer (PET-RAFT) polymerization was identified through a systematic catalyst design and discovery. The devised OPC offers excellent control over PET-RAFT polymerizations of methyl methacrylate at very low catalyst loadings (5 ppm), that is, ca. 5–50 times lower loadings than other OPCs reported so far. Moreover, excellent oxygen tolerance was achieved using the discovered OPC combined with trithiocarbonate-based chain-transfer agent (CTA) under low-energy light irradiation conditions. In depth experimental and computational investigations revealed that (1) strong visible-light absorption and efficient generation of long-lived triplet states of the OPC due to its unique molecular structure and (2) the oxidation stability and no rate retardation of trithiocarbonate-based CTA are the key to the outstanding oxygen tolerance and ppm-level catalyst loadings. Our approach is thus believed to address a variety of challenging tasks related to polymer synthesis and living additive manufacturing.

Metal-free atom transfer radical polymerization: reaching ppm catalyst loading under sunlight

“…24,26,43 To our delight, this control on low dispersity is even better than that with dihydroacridine photocatalysts which were developed especially for this type of monomers very recently. 43 In addition, ODA photocatalysts could also mediate the reversible addition-fragmentation chain transfer (RAFT) polymerization [48][49][50] of MMA at low ppm catalyst loading (1-10 ppm) under sunlight, with excellent control and narrow dispersity (Đ < 1.10, entries [15][16][17], which are comparable to the precious iridium photocatalyst 51 (Supplementary Table 7).…”

“…Notably, ODA 5d also represent a rare example of organic photocatalysts that could promote the polymerization of both MMA and BA, as well as RAFT polymerization of MMA with good controls. 43,49 In summary, a catalyst design logic based on heteroatom-doping of polycyclic arenes has been successfully introduced into the development of new photocatalysts for organocatalyzed atom transfer radical polymerization (O-ATRP). Oxygen-doped antratherene (ODA) has been identified as a novel catalyst framework with unprecedented high efficiency, featuring its strong visible light absorption and excellent performance at extremely low catalyst loadings in both organocatalyzed ATRP and RAFT polymerization.…”

Emerging Organic Photoredox Catalysts for Organic Transformations

“…4DPAIPN where diphenylamine substituted for the carbazole of 4CzIPN ( 1 ) was synthesized in the aforementioned publications by Zhang and co‐workers, but later it turned out to be 3DPAFIPN ( 15 ). Therefore, the photophysical properties and catalytic performance of 3DPAFIPN ( 15 ) and 4DPAIPN ( 25 , appeared after then, , ) are not mentioned here for clarity.…”

“…Some of the developed PCs ( 161 , 165 , 168 , and 185 ) were selected based on ground‐/excited‐state redox potentials and triplet excited‐state energy and used for the PET‐RAFT polymerization of MMA in our work . 165 ( 4DP‐IPN ) outperformed other PCs, i.e.…”

Light and magnetism dual-gated photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization

“…This so-called PET-RAFT is mediated by photocatalysts that can transfer electrons from excited states to chain transfer agents (CTAs) to generate radicals with the irradiation of light and initiate polymerization. 23 Visible light, 24 near-infrared light and far-red light-induced 25 RAFT polymerizations at various wavelength bands have gained wide attention.…”