CuBr2/Me6TREN-mediated living radical polymerization of methyl methacrylate at ambient temperature

Unraveling the Roles of Amines in Atom Transfer Radical Polymerization in the Dark

Multidentate amines have been widely used as ligands (L) for Cu-catalysts in atom transfer radical polymerization (ATRP) and as electron donors in photochemically induced polymerizations. However, mechanistic aspects of the role of amines in ATRP in the dark have remained elusive. Herein, the structure-activity relationship and the related electron transfer reactions with Br-CuII/L complexes and/or with alkyl bromides (R-Br) were investigated for 25 amines. Amines function as electron donors and reducing agents for Br-CuII/L complexes via an outer sphere electron transfer (OSET) mechanism, enabling slow but continuous generation of CuI/L activators and inducing controlled ATRP. However, two amines, diazabicyclo(5.4.0)undec-7-ene (DBU) and 1,1,3,3-tetramethylguanidine (TMG), reduced Br-CuII/L faster, suggesting an inner sphere electron transfer (ISET) process. ATRP, starting with initial deactivators (Br-CuII/L) species, proceeded in the dark in the presence of an excess of tertiary amines, such as tris[2-(dimethylamino)ethyl]amine (Me6TREN), 1,4-diazabicyclo[2.2.2]octane (DABCO), and TMG at room temperature and afforded polymers with low dispersities (Đ ≤ 1.15). With copper(II) triflate complex (CuII/L+2, -(OTf)2), which has a more positive reduction potential, ATRP proceeded at room temperature with several inexpensive secondary and tertiary amines including triethylamine (TEA) and dimethylethanolamine (DMAE). Interestingly, multidentate amines also served as direct R-Br activators at elevated temperatures (60 °C). In all cases, chains were initiated with R-Br and not by the amine radical cations as byproducts of electron transfer. Amines also enabled ATRP in the presence of residual air in flasks with a large headspace, underpinning them as a robust and accessible reducing agent for practical applications.

Better Together: Photoredox/Copper Dual Catalysis in Atom Transfer Radical Polymerization

Photomediated Atom Transfer Radical Polymerization (photoATRP) is an activator regeneration method, which allows for the controlled synthesis of well-defined polymers via light irradiation. Traditional photoATRP is often limited by the need for high-energy ultraviolet or violet light. These could negatively affect the control and selectivity of the polymerization, promote side reactions, and may not be applicable to biologically relevant systems. This drawback can be circumvented by an introduction of the catalytic amount of photocatalysts, which absorb visible and/or NIR light and, therefore, controlled, regenerative ATRP can be performed with the dual-catalytic cycle. Herein, a critical summary of recent developments in the field of dual-catalysis concerning Cu-catalyzed ATRP is provided. Contributions of involved species are examined mechanistically, followed by challenges and future directions towards the next generation of advanced functional macromolecular materials.

Facile, simple, and inexpensive ionic liquid, 1-phenyl-3-methylimidazole diphenyl phosphate, as an efficient phosphorus-based ligand for copper-catalyzed reverse atom transfer radical polymerization of methyl methacrylate

A facile, simple, and inexpensive ionic liquid, 1-phenyl-3-methylimidazole diphenyl phosphate has been successfully used as an efficient phosphorus ligand for CuBr₂-mediated reverse ATRP.

A facile, simple, and inexpensive ionic liquid, 1-alkyl-3-methylimidazole chloride, as ligand for the iron(iii)-mediated reverse atom transfer radical polymerization of methyl methacrylate

The facile, simple, and inexpensive ILs, 1-alkyl-3-methylimidazole chloride ([Rmim][Cl]), are explored for the first time as ligands for the reverse ATRP of methacrylates.

Visible-light induced controlled radical polymerization of methacrylates with Cu(dap)2Cl as a photoredox catalyst

Under visible light irradiation, block copolymers of PPEGMA-b-PMMA with high molecular weights and narrow molecular weight distributions are obtained starting from a PPEGMA macroinitiator in the presence of the Cu(dap)₂Cl/Me₆TREN catalytic system.