Facile Iron-Mediated AGET ATRP for Water-Soluble Poly(ethylene glycol) Monomethyl Ether Methacrylate in Water

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-Catalysed Radical Polymerisation by Living Bacteria

The ability to harness cellular redox processes for abiotic synthesis might allow the preparation of engineered hybrid living systems. Towards this goal we describe a new bacteria-mediated iron-catalysed reversible deactivation radical polymerisation (RDRP), with a range of metal-chelating agents and monomers that can be used under ambient conditions with a bacterial redox initiation step to generate polymers. Cupriavidus metallidurans, Escherichia coli, and Clostridium sporogenes species were chosen for their redox enzyme systems and evaluated for their ability to induce polymer formation. Parameters including cell and catalyst concentration, initiator species, and monomer type were investigated. Water-soluble synthetic polymers were produced in the presence of the bacteria with full preservation of cell viability. This method provides a means by which bacterial redox systems can be exploited to generate "unnatural" polymers in the presence of "host" cells, thus setting up the possibility of making natural-synthetic hybrid structures and conjugates.

Axially Ligated Mesohemins as Bio-Mimicking Catalysts for Atom Transfer Radical Polymerization

Copper is the most common metal catalyst used in atom transfer radical polymerization (ATRP), but iron is an excellent alternative due to its natural abundance and low toxicity compared to copper. In this work, two new iron-porphyrin-based catalysts inspired by naturally occurring proteins, such as horseradish peroxidase, hemoglobin, and cytochrome P450, were synthesized and tested for ATRP. Natural protein structures were mimicked by attaching imidazole or thioether groups to the porphyrin, leading to increased rates of polymerization, as well as providing polymers with low dispersity, even in the presence of ppm amounts of catalysts.

γ-valerolactone (GVL) as a bio-based green solvent and ligand for iron-mediated AGET ATRP

In this paper, γ-valerolactone (GVL), a bio-based polar solvent, was applied as green solvent for iron(III)-catalyzed AGET ATRP without any external ligand. GVL is a fully degradable, non-toxic green solvent and has complex ability to iron halide complexes through –OCO- group. GVL as the solvent and the ligand for AGET ATRP of MMA in a controlled manner, as proved by kinetic study, the low PDI values and the increase in polymer molecular weight versus monomer conversion. Chain re-initiation experiments and 1HNMR characterization were conducted to further confirm the living feature.

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.

Design of a hydrophilic ruthenium catalyst for metal-catalyzed living radical polymerization: highly active catalysis in water

A novel hydrophilic phosphine ligand for a ruthenium catalyst was synthesized towards useful living radical polymerization in water.

Real-time monitoring of a controlled drug delivery system in vivo: construction of a near infrared fluorescence monomer conjugated with pH-responsive polymeric micelles

A self-assembled polymeric micelle from multifunctional amphiphilic copolymer with NIR and pH-sensitive groups can be used to monitor the dynamic process of its arriving at the tumor site in real time.

Recent Progress on Transition Metal Catalyst Separation and Recycling in ATRP

Atom transfer radical polymerization (ATRP) is a versatile and robust tool to synthesize a wide spectrum of monomers with various designable structures. However, it usually needs large amounts of transition metal as the catalyst to mediate the equilibrium between the dormant and propagating species. Unfortunately, the catalyst residue may contaminate or color the resultant polymers, which limits its application, especially in biomedical and electronic materials. How to efficiently and economically remove or reduce the catalyst residue from its products is a challenging and encouraging task. Herein, recent advances in catalyst separation and recycling are highlighted with a focus on (1) highly active ppm level transition metal or metal free catalyzed ATRP; (2) post-purification method; (3) various soluble, insoluble, immobilized/soluble, and reversible supported catalyst systems; and (4) liquid-liquid biphasic catalyzed systems, especially thermo-regulated catalysis systems.

Iron-catalyzed atom transfer radical polymerization

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

Iron-mediated AGET ATRP with crown ether as both ligand and solvent

A facile iron-mediated AGET ATRP system suitable for a wide range of monomers was successfully developed with crown ether without any additional ligands.

Thermoregulated phase transfer catalysis in aqueous/organic biphasic system: facile and highly efficient ATRP catalyst separation and recycling in situ using typical alkyl halide as initiator

An important development of TRPTC-based ICAR ATRP for metal catalyst separation and recycling in an aqueous/organic biphasic system was achieved with alkyl halide as the initiator for the first time.

Magnetic nanomaterials with near-infrared pH-activatable fluorescence via iron-catalyzed AGET ATRP for tumor acidic microenvironment imaging

This work provides a fluorescent/magnetic iron oxide nanomaterials prototype to visualize the solid tumor in vivo by sensing the tumor acidic microenvironment, and a satisfactory tumor-to-normal tissue signal ratio (T/N ratio) and a prolonged time-window for 4T1 tumor visualization were observed in vivo.

Fabrication and photoactivity of a tunable-void SiO₂-TiO₂ core-shell structure on modified SiO₂ nanospheres by grafting an amphiphilic diblock copolymer using ARGET ATRP

SiO₂-based composites have important applications in various technological fields. In this work, a tunablevoid SiO₂-TiO₂ core-shell structure was successfully prepared for the first time using SiO₂-polymethyl methacrylate (PMMA)-polyoligo(ethylene glycol)methyl ether methacrylate (PO(EO)nMA) (n = 2, 5, and 8). An amphiphilic copolymer was used as the template, and calcination was performed using tetrabutyl titanate (TBT) as the titanium source. SiO₂-PMMA-b-PO(EO)nMA microspheres were first synthesized through activators regenerated by electron transfer-atom transfer radical polymerization. Methyl methacrylate and O(EO)nMA were grafted with different EO unit numbers onto the surface of the halogen functional group of SiO₂. TBT was hydrolyzed along with the PO(EO)nMA chain through hydrogen bonding, and then the SiO₂-TiO₂ core-shell structure was acquired through calcination to remove the polymer. Simultaneously, amorphous TiO₂ crystallized during calcination. A series of characterizations indicated that the amphiphilic block copolymer was grafted onto SiO₂ mesoparticle surfaces, the titania samples existed only in the anatase phase, and the prepared SiO₂-TiO₂ had hierarchically nanoporous structures. The gradient hydrophilicity of the PMMA-b-PO(EO)nMA copolymer template facilitated the hydrolysis of TBT molecules along the PO(EO)nMA to PMMA segments, thereby tuning the space between the core and the shell. In addition, the space was about 6 nm when the EO number was 2, and the space was about 10 nm when the EO numbers were 5 and 8. The photocatalytic activities of the SiO₂-TiO₂ materials were tested on the photodegradation of methyl orange.

Bifunctional nanoparticles with magnetism and NIR fluorescence: controlled synthesis from combination of AGET ATRP and 'click' reaction

In this work, bifunctional nanoparticles (NPs) capable of emitting near infrared (NIR) fluorescence and generating superparamagnetism under an external magnetic field were prepared by combination of 'click' reaction and surface-initiated activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) of water-soluble poly(ethylene glycol) monomethyl ether methacrylate (PEGMA) and glycidyl methacrylate (GMA) using biocompatible iron as the catalyst on the surface of silica-coated iron oxide (Fe3O4@SiO2) NPs. The nanosized Fe3O4@SiO2@PPEGMA-co-PGMA@N3 was prepared through AGET ATRP and alkynyl bearing NIR dye was also prepared; afterwards they were integrated together by 'click' reaction. The different stages of surface modification were approved by employing different characterization techniques such as TEM, XRD, XPS, VSM and FT-IR, and the properties of the final NPs were thoroughly studied. Their suitability as dual model imaging agents for magnetic resonance (MR) and fluorescence imaging was investigated, indicating them to be a competitive candidate for imaging contrast agents.

Thermo-regulated phase separable catalysis (TPSC)-based atom transfer radical polymerization in a thermo-regulated ionic liquid

A thermo-regulated phase separable catalysis (TPSC) system for AGET ATRP based on a thermo-regulated ionic liquid was developed for the first time. The corresponding transition metal catalysts could be easily recovered and reused several times with negligible loss of catalytic activity.