Photoinduced Organocatalyzed Atom Transfer Radical Polymerization Using Low ppm Catalyst Loading

Photoinduced
organocatalyzed atom-transfer radical polymerization
(O-ATRP) is a controlled radical polymerization methodology that can
be mediated by organic photoredox catalysts under the influence of
light. However, typical O-ATRP systems require relatively high catalyst
loadings (1000 ppm) to achieve control over the polymerization. Here,
new core-extended diaryl dihydrophenazine photoredox catalysts were
developed for O-ATRP and demonstrated to efficiently operate at low
catalyst loadings of 5–50 ppm to produce polymers with excellent
molecular weight control and low dispersity, while achieving near-quantitative
initiator efficiency. Photophysical and electrochemical properties
of the catalysts were computationally predicted and experimentally
measured to correlate these properties with improved catalytic performance.
Furthermore, these catalysts were utilized to synthesize materials
with complex architectures, such as triblock copolymers and star polymers.
To demonstrate their broad utility, polymerizations employing these
catalysts were successfully scaled up to 5 g and revealed to efficiently
operate under air.