Visible-Light-Induced Atom-Transfer-Radical Polymerization with a ppm-Level Iron Catalyst

Abstract

A low-ppm-level iron (Fe)-based photoinduced atom-transfer-radical polymerization (ATRP) under visible-light irradiation was developed. Various ligands, tris(4-methoxyphenyl)phosphine (TMPP), 4,4′-dinonyl-2,2′-dipyridyl (dNbpy), and tris[2-(dimethylamino)ethyl]amine (Me 6 TREN), were used to enhance the catalytic activity of Fe complexes. Activator Fe II complexes were formed by the reduction of Fe III complexes with a monomer under visible-light irradiation. Linear semilogarithmic plots and low polydispersities (M w /M n < 1.4) were achieved, indicating that low-ppm-level Fe-based photoinduced ATRP was well-controlled. The effect of the catalyst concentration on polymerization was evaluated. A reduction of catalyst loadings resulted in increased polymerization rate and molecular weight. The order of Fe complex activity for the ligand was TMPP > dNbpy > Me 6 TREN. Additionally, this polymerization could be ceased and restarted, responding to light off and light on. Retention of the chain-end functionality was analyzed by 1 H NMR and chainextension experiments. Results showed that the partial chain-end functionality of the resulting polymers was lost. Thus, there is still room for improvement of the chain-end functionality and initiation efficiency of the resulting polymers.

Photoinitiated Metal Free Living Radical and Cationic Polymerizations

“…The process is based on successive Mn 2 (CO) 10 assisted visible light radical generation, oxidation addition and deactivation reactions. Obviously, the methodologies described here for both radical, cationic routes and their combinations are expected to be useful to prepare materials with controlled molecular weight and functionality particularly those involving bio-applications, where excess inorganic residuals might be a disadvantage.…”

“…More recently, Yagci and coworkers [74] reported a novel photoinitiating system for living cationic polymerization of vinyl ethers eliminating the requirement for the metal halides by using Mn 2 (CO) 10 photochemistry. As presented in Scheme 10, in the described approach, visible-light irradiation of Mn 2 (CO) 10 in the presence of an alkyl bromide results in the formation of carbon-centered radicals.…”

“…As presented in Scheme 10, in the described approach, visible-light irradiation of Mn 2 (CO) 10 in the presence of an alkyl bromide results in the formation of carbon-centered radicals. The photochemically generated radicals are then oxidized by diphenyliodonium ions to the corresponding cations.…”

“…Combining photoinduced electron transfer reactions developed for the conventional systems with controlled polymerization techniques has recently revolutionized the synthesis of well-defined macromolecular architectures [6]. Many attempts have been devoted to apply photochemical systems to existing controlled/living polymerization methodologies by photochemically effecting initiation, mediation and control of these processes [7][8][9][10][11][12][13][14][15][16][17][18][19].…”

Assessment of Microwave Effect on Polymerization Conducted under ARGET ATRP Conditions

“…However, with the development of ATRP, the concentration of catalyst loading can be decreased to parts per million (ppm) level with good controllability. These methods include activators regenerated by electron transfer (ARGET) ATRP, initiators for continuous activator regeneration (ICAR) ATRP supplemental activator and reducing agent (SARA) ATRP, electrochemically mediated ATRP (eATRP) and photomediated ATRP (photoATRP) …”