Open AccessRadical Addition to N,N-Diaryl Dihydrophenazine Photoredox Catalysts and Implications in Photoinduced Organocatalyzed Atom Transfer Radical Polymerization
Author(s) -
Daniel A. Corbin,
Katherine O. Puffer,
Katherine A. Chism,
Justin P. Cole,
Jordan C. Theriot,
Blaine G. McCarthy,
Bonnie L. Buss,
ChernHooi Lim,
Sarah R. Lincoln,
Brian S. Newell,
Garret M. Miyake
Publication year - 2021
Publication title -
macromolecules
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.994
H-Index - 313
eISSN - 1520-5835
pISSN - 0024-9297
DOI - 10.1021/acs.macromol.1c00501
Subject(s) - atom transfer radical polymerization , dispersity , polymerization , chemistry , polymer chemistry , radical polymerization , cobalt mediated radical polymerization , photoredox catalysis , living free radical polymerization , radical , catalysis , living polymerization , polymer , nitroxide mediated radical polymerization , photochemistry , organic chemistry , photocatalysis
Photoinduced organocatalyzed atom transfer radical polymerization (O-ATRP) is a controlled radical polymerization methodology catalyzed by organic photoredox catalysts (PCs). In an efficient O-ATRP system, good control over molecular weight with an initiator efficiency ( I * = M n,theo / M n,exp × 100%) near unity is achieved, and the synthesized polymers possess a low dispersity ( Đ ). N , N -Diaryl dihydrophenazine catalysts typically produce polymers with low dispersity ( Đ < 1.3) but with less than unity molecular weight control ( I * ~ 60-80%). This work explores the termination reactions that lead to decreased control over polymer molecular weight and identifies a reaction leading to radical addition to the phenazine core. This reaction can occur with radicals generated through reduction of the ATRP initiator or the polymer chain end. In addition to causing a decrease in I *, this reactivity modifies the properties of the PC, ultimately impacting polymerization control in O-ATRP. With this insight in mind, a new family of core-substituted N , N -diaryl dihydrophenazines is synthesized from commercially available ATRP initiators and employed in O-ATRP. These new core-substituted PCs improve both I * and Đ in the O - ATRP of MMA, while minimizing undesired side reactions during the polymerization. Further, the ability of one core-substituted PC to operate at low catalyst loadings is demonstrated, with minimal loss of polymerization control down to 100 ppm (weight average molecular weight [ M w ] = 10.8 kDa, Đ = 1.17, I * = 104% vs M w = 8.26, Đ = 1.10, I * = 107% at 1000 ppm) and signs of a controlled polymerization down to 10 ppm of the catalyst ( M w = 12.1 kDa, Đ = 1.36, I * = 107%).