Color-Coding Visible Light Polymerizations To Elucidate the Activation of Trithiocarbonates Using Eosin Y

Abstract

We report mechanistic investigations into aqueous visible-light reversible addition−fragmentation chain transfer (RAFT) polymerizations of acrylamides using eosin Y as a photoinduced electron-transfer (PET) catalyst. The photoinduced polymerization was found to be dependent upon the irradiation wavelength and reagents, where either reduction or oxidation of the PET catalyst leads to inherently different initiation and reversible-termination steps. Using blue light, multiple mechanisms of initiation are observed, depending on the presence or absence of a sacrificial reducing agent. Using green light, both an oxidative and a reductive PET initiation mechanism can be pursued. Investigations into the role of PET catalyst, wavelength, and reducing agent demonstrated that precise polymers with predictable molecular weights are best realized under an oxidative PET-RAFT mechanism. Therefore, this study provides fundamental insight into visible-light RAFT photopolymerizations and the role of eosin Y as a photoredox catalyst.

An Oxygen Paradox: Catalytic Use of Oxygen in Radical Photopolymerization

“…To our amazement, only the nondeoxygenated reaction achieved polymerization with an excellent agreement between the theoretical and experimental (GPC) molecular weights (M n ), and an arrow molecular weight distribution (MWD, M w /M n = 1.09). [17] To test this hypothesis,w ea dded triethylamine (TEA) at 1equivalence to the trithiocarbonate for the polymerization of MA under both aerobic and anaerobic conditions (Supporting Information, Table S1, entries 5,6). [6] Kinetic investigation of N,N-dimethylacrylamide (DMA) under aerobic conditions revealed that the polymerization progressed in al inear fashion after as hort (ca.…”

Photochemistry for Well‐Defined Polymers in Aqueous Media: From Fundamentals to Polymer Nanoparticles to Bioconjugates

“…This means that there is a high likelihood of being able to expand the method to proteins which are more sensitive to the presence of small organic molecules. A mechanistic study on this type Eosin Y catalyzed PET‐RAFT has been very recently performed by Sumerlin and coworkers …”

“…b) Esterase activity against p‐ NP of conjugate and lipase adsorbed on a glass slide after drying and washing. Reproduced with permission . Copyright 2018, Elsevier.…”

Continuous Flow Photoinduced Reversible Deactivation Radical Polymerization

“…Photo‐RAFT with photoinitiator, RAFT without exogenous catalyst/initiator (iniferter), and photoinduced electron/energy transfer RAFT (PET‐RAFT) have roused growing concern for the well‐controlled features and the accelerated polymerization rates . More recently, a library of photocatalysts including phthalocyanine compounds, Eosin Y, zinc tetraphenylporphyrin (ZnTPP) and crude extracted chlorophyll were disclosed, which could mediate the polymerizations under visible and near‐infrared light even in the presence of oxygen . The combination of microflow technique and photoinduced RAFT and iniferter polymerization will be discussed below.…”