Development of Environmentally Friendly Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) is one of the most successful techniques for the preparation of well-defined polymers with controllable molecular weights, narrow molecular weight distributions, specific macromolecular architectures, and precisely designed functionalities. ATRP usually involves transition-metal complex as catalyst. As the most commonly used copper complex catalyst is usually biologically toxic and environmentally unsafe, considerable interest has been focused on iron complex, enzyme, and metal-free catalysts owing to their low toxicity, inexpensive cost, commercial availability and environmental friendliness. This review aims to provide a comprehensive understanding of iron catalyst used in normal, reverse, AGET, ICAR, GAMA, and SARA ATRP, enzyme as well as metal-free catalyst mediated ATRP in the point of view of catalytic activity, initiation efficiency, and polymerization controllability. The principle of ATRP and the development of iron ligand are briefly discussed. The recent development of enzyme-mediated ATRP, the latest research progress on metal-free ATRP, and the application of metal-free ATRP in interdisciplinary areas are highlighted in sections. The prospects and challenges of these three ATRP techniques are also described in the review.

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.

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.

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.

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.

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.

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.

Atom transfer radical polymerization by solvent-stabilized (Me3TACN)FeX2: a practical access to reusable iron(ii) catalysts

A new Fe(ii) complex, (Me₃TACN)FeBr₂(κ-NCMe), was prepared as an efficient and reusable catalyst for atom transfer radical polymerization.

Iron-catalyzed atom transfer radical polymerization

This article reviews the preparation of polymers using iron-catalyzed atom transfer radical polymerization.