Organocatalyzed Atom Transfer Radical Polymerization: Perspectives on Catalyst Design and Performance

Abstract

The recent development of organocatalyzed atom transfer radical polymerization (O-ATRP) represents a significant advancement in the field of controlled radical polymerizations. A number of classes of photoredox catalysts have been employed thus far in O-ATRP. Analysis of the proposed mechanism gives insight into the relevant photophysical and chemical properties that determine catalyst performance. Discussion of each of the classes of O-ATRP catalysts highlights their previous uses, their roles in the development of O-ATRP, and the distinctive properties that govern their polymerization behavior, leading to a set of design principles for O-ATRP catalysts. Remaining challenges for O-ATRP are presented, as well as prospects for further improvement in the application scope of O-ATRP.

Impact of Light Intensity on Control in Photoinduced Organocatalyzed Atom Transfer Radical Polymerization

“…1–5 Organocatalyzed atom transfer radical polymerization (O-ATRP) has recently emerged as a methodology to produce well-defined polymers without the use of metal catalysts. 6 Since initial reports that perylene 7 and phenylphenothiazine 8 could operate O-ATRP, more organic photoredox catalysts (PCs) have been introduced, including several diaryl dihydrophenazine, 9–11 carbazole, 12 phenoxazine, 13 anthracene/pyrene, 14 and other phenothiazine 15–18 derivatives. A proposed mechanism of O-ATRP proceeds through an oxidative quenching pathway which consists of five main processes: (1) photoexcitation of the ground state PC to a singlet excited state ( 1 PC*); (2) intersystem crossing to a triplet excited state ( 3 PC*); 9,19 (3) direct reduction of an alkyl halide initiator or polymer chain end by 3 PC*, generating an active radical for polymerization propagation and formation of a radical cation/halide anion “deactivator” complex (PC •+ /X − ); (4) polymer MW growth via polymerization propagation; and (5) oxidation of the active radical by PC •+ /X − to reversibly deactivate the polymerization and regenerate PC (Figure 1).…”

How the catalyst circulates and works in organocatalyzed atom transfer radical polymerization

“…[1][2][3] This technique provides the capability to synthesize well-defined functional polymers with a wide range of monomer types under mild conditions. [8][9][10][11][12][13][14][15][16][17][18] In O-ATRP systems, the organic photoredox catalysts (PCs) could completely replace transition metal catalysts. The high cost of post purification makes this technique losing competitiveness in terms of industrial application.…”

Visible-Light-Promoted C–S Cross-Coupling via Intermolecular Charge Transfer

“…In our early attempts to achieve visible-light-promoted and transition-metal-free conditions for C–S cross-coupling, we applied strongly reducing N , N -diaryldihydrophenazines 9a or N -arylphenoxazines 9b as organic photoredox catalysts, which we previously developed for use in organocatalyzed atom transfer radical polymerization as well as in small-molecule transformations. 9c,d We hypothesized that these organic photoredox catalysts, in the photoexcited state, could directly reduce an aryl halide and generate a radical anion capable of partaking in C–S bond formation.…”

“…9c,d We hypothesized that these organic photoredox catalysts, in the photoexcited state, could directly reduce an aryl halide and generate a radical anion capable of partaking in C–S bond formation. 10 Encouragingly, we observed the C–S cross-coupled product in high yield with white light-emitting diode (LED) irradiation of a solution containing 4′-bromoacetophe-none ( 1a ), 4-methylbenzenethiol ( 2a ), Cs 2 CO 3 , and the organic photoredox catalyst 5,10-di-1-naphthyl-5,10-dihydrophenazine in dimethyl sulfoxide (DMSO).…”