Kinetics of Fe-Mediated ATRP with Triarylphosphines

Electrochemical Investigation of Iron-Catalyzed Atom Transfer Radical Polymerization

Use of iron-based catalysts in atom transfer radical polymerization (ATRP) is very interesting because of the abundance of the metal and its biocompatibility. Although the mechanism of action is not well understood yet, iron halide salts are usually used as catalysts, often in the presence of nitrogen or phosphorous ligands (L). In this study, electrochemically mediated ATRP (eATRP) of methyl methacrylate (MMA) catalyzed by FeCl3, both in the absence and presence of additional ligands, was investigated in dimethylformamide. The electrochemical behavior of FeCl3 and FeCl3/L was deeply investigated showing the speciation of Fe(III) and Fe(II) and the role played by added ligands. It is shown that amine ligands form stable iron complexes, whereas phosphines act as reducing agents. eATRP of MMA catalyzed by FeCl3 was investigated in different conditions. In particular, the effects of temperature, catalyst concentration, catalyst-to-initiator ratio, halide ion excess and added ligands were investigated. In general, polymerization was moderately fast but difficult to control. Surprisingly, the best results were obtained with FeCl3 without any other ligand. Electrogenerated Fe(II) effectively activates the dormant chains but deactivation of the propagating radicals by Fe(III) species is less efficient, resulting in dispersity > 1.5, unless a high concentration of FeCl3 is used.

Effect of halogen and solvent on iron-catalyzed atom transfer radical polymerization

Efficient exchange of Br in iron-catalyzed ATRP in anisole provided well-controlled polymers with low dispersity as opposed to the Cl-based initiating system, which resulted in large dispersities due to the slower activation/deactivation with Cl.

Iron Catalysts in Atom Transfer Radical Polymerization

Catalysts are essential for mediating a controlled polymerization in atom transfer radical polymerization (ATRP). Copper-based catalysts are widely explored in ATRP and are highly efficient, leading to well-controlled polymerization of a variety of functional monomers. In addition to copper, iron-based complexes offer new opportunities in ATRP catalysis to develop environmentally friendly, less toxic, inexpensive, and abundant catalytic systems. Despite the high efficiency of iron catalysts in controlling polymerization of various monomers including methacrylates and styrene, ATRP of acrylate-based monomers by iron catalysts still remains a challenge. In this paper, we review the fundamentals and recent advances of iron-catalyzed ATRP focusing on development of ligands, catalyst design, and techniques used for iron catalysis in ATRP.

Poly (Ethylene Oxide)-Based Block Copolymer Electrolytes Formed via Ligand-Free Iron-Mediated Atom Transfer Radical Polymerization

The Br-terminated poly (ethylene oxide) (PEO-Br) is used as a green and efficient macroinitiator in bulk Fe-catalyzed atom transfer radical polymerization (ATRP) without the addition of any organic ligands. The polymerization rate is able to be mediated by PEO-Br with various molecular weights, and the decrease in redox potential of FeBr₂ in cyclic voltammetry (CV) curves indicates that an increased coordination effect is deteriorated with the depressing reaction activity in the longer ethylene oxide (EO) chain in PEO-Br. In combination with the study of different catalysts and catalytic contents, the methyl metharylate (MMA) or poly (ethylene glycol) monomethacrylate (PEGMA) was successfully polymerized with PEO-Br as an initiator. This copolymer obtained from PEGMA polymerization can be further employed as a polymer matrix to form the polymer electrolyte (PE). The higher ionic conductivity of PE was obtained by using a high molecular weight of copolymer.

Ligand- and solvent-free ATRP of MMA with FeBr3 and inorganic salts

A new cost-effective and safe protocol for the bulk ATRP of MMA uses FeBr₃, EBrPA and an inorganic compound (carbonate, bicarbonate, phosphate, hydroxide, chloride, bromide) of an alkali metal cation.

Organocatalyzed atom transfer radical polymerization (ATRP) using triarylsulfonium hexafluorophosphate salt (THS) as a photocatalyst

Triarylsulfonium hexafluorophosphate salt (THS), an organic and inexpensive compound, was employed as a photocatalyst for metal free atom transfer radical polymerization (ATRP) of methacrylate monomers.

Iron-Catalyzed Atom Transfer Radical Polymerization of Semifluorinated Methacrylates

Fluorinated polymers are an important class of functional materials that exhibit unique properties such as high chemical resistance, thermal stability, and low surface energy. Atom transfer radical polymerization (ATRP) of semifluorinated monomers catalyzed by copper catalysts often requires development of special conditions to control the polymerization and prevent side reactions such as base-catalyzed transesterification between the fluoro-containing monomers and solvents. In this paper, photoinduced iron-catalyzed ATRP was applied to the polymerization of a variety of semifluorinated methacrylate monomers. Polymerizations were initiated by photochemical generation of the Fe catalyst activator under blue light irradiation, enabling temporal control over the growth of polymer chains, and were well-controlled in various solvents, including fluorinated and nonfluorinated solvents, without undergoing any side reactions. Moreover, in situ chain extension and block copolymerization experiments demonstrated the preservation of chain end functionality, enabling facile synthesis of well-controlled block copolymers.

Bromoalkyl ATRP initiator activation by inorganic salts: experiments and computations

The bromoalkyl ATRP initiator EBrPA is activated by many alkali, alkaline-earth and ammonium salts, leading to MMA polymerization, but only the iodides yield a controlled process because of a degenerative transfer mechanism contribution.

Iron-catalysed atom transfer radical polyaddition for the synthesis and modification of novel aliphatic polyesters displaying lower critical solution temperature and pH-dependent release behaviors

Novel aliphatic polyesters were synthesized and quantitatively modified by click reactions to obtain amphiphilic polymer brushes for nano-carrier applications.

Normal, ICAR and photomediated butadiene-ATRP with iron complexes

FeX₂ or FeX₃ (X = Cl ≫ Br) alone or with P ≫ X > O > N > C ligands and bromoester initiators enable the successful ATRP of butadiene in toluene at 110 °C.

Addressing the role of triphenylphosphine in copper catalyzed ATRP

A new Atom Transfer Radical Polymerization (ATRP) process with triphenylphosphine (PPh₃) and [Cu^IIMe₆TREN]²⁺ as the catalyst system is reported.

Photoinduced Fe-mediated atom transfer radical polymerization in aqueous media

Photoinduced atom transfer radical polymerization with an Fe catalyst was successfully performed in aqueous media for the first time.

Photocatalyzed iron-based ATRP of methyl methacrylate using 1,3-dimethyl-2-imidazolidinone as both solvent and ligand

A simple photocatalyzed Fe-based ATRP of MMA was conducted under UV irradiation using the “green” solvent DMI as both the solvent and ligand.

Iron-Mediated Homogeneous ICAR ATRP of Methyl Methacrylate under ppm Level Organometallic Catalyst Iron(III) Acetylacetonate

Atom Transfer Radical Polymerization (ATRP) is an important polymerization process in polymer synthesis. However, a typical ATRP system has some drawbacks. For example, it needs a large amount of transition metal catalyst, and it is difficult or expensive to remove the metal catalyst residue in products. In order to reduce the amount of catalyst and considering good biocompatibility and low toxicity of the iron catalyst, in this work, we developed a homogeneous polymerization system of initiators for continuous activator regeneration ATRP (ICAR ATRP) with just a ppm level of iron catalyst. Herein, we used oil-soluble iron (III) acetylacetonate (Fe(acac)₃) as the organometallic catalyst, 1,1'-azobis (cyclohexanecarbonitrile) (ACHN) with longer half-life period as the thermal initiator, ethyl 2-bromophenylacetate (EBPA) as the initiator, triphenylphosphine (PPh₃) as the ligand, toluene as the solvent and methyl methacrylate (MMA) as the model monomer. The factors related with the polymerization system, such as concentration of Fe(acac)₃ and ACHN and polymerization kinetics, were investigated in detail at 90 °C. It was found that a polymer with an acceptable molecular weight distribution (Mw/Mn = 1.43 at 45.9% of monomer conversion) could be obtained even with 1 ppm of Fe(acac)₃, making it needless to remove the residual metal in the resultant polymers, which makes such an ICAR ATRP process much more industrially attractive. The "living" features of this polymerization system were further confirmed by chain-extension experiment.