Iron(III)‐mediated AGET ATRP of styrene using tris(3,6‐dioxaheptyl)amine as a ligand

A commercially available tris(3,6‐dioxaheptyl)amine (TDA‐1) was used as a novel ligand for activator generated by electron transfer atom transfer radical polymerization (AGET ATRP) of styrene in bulk or solution mediated by iron(III) catalyst in the presence of a limited amount of air. FeCl₃ · 6H₂O and (1‐bromoethyl)benzene (PEBr) were used as the catalyst and initiator, respectively; and environmentally benign ascorbic acid (VC) was used as the reducing agent. The polymerizations show the features of “living”/controlled free‐radical polymerizations and well‐defined polystyrenes with molecular weight M_n = 2400–36,500 g/mol and narrow polydispersity (M_w/M_n = 1.11–1.29) were obtained. The “living” feature of the obtained polymer was further confirmed by a chain‐extension experiment. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2002–2008, 2009     

Iron‐mediated AGET ATRP of methyl methacrylate using metal wire as reducing agent

Methyl methacrylate (MMA) were successfully polymerized by atom transfer radical polymerization with activator generated by electron transfer (AGET ATRP) using copper or iron wire as the reducing agent at 90°C. Well‐controlled polymerizations were demonstrated using an oxidatively stable iron(III) chloride hexahydrate (FeCl₃·6H₂O) as the catalyst, ethyl 2‐bromoisobutyrate (EBiB) as the initiator, and tetrabutylammonium bromide (TBABr) or triphenylphosphine as the ligand. The polymerization rate was fast and affected by the amount of catalyst and type of reducing agents. For example, the polymerization rate of bulk AGET ATRP with a molar ratio of [MMA]₀/[EBiB]₀/[FeCl₃·6H₂O]₀/[TBABr]₀ = 500/1/0.5/1 using iron wire (the conversion reaches up to 82.2% after 80 min) as the reducing agent was faster than that using copper wire (the conversion reaches up to 86.1% after 3 h). At the same time, the experimental M_n values of the obtained poly(methyl methacrylate) were consistent with the corresponding theoretical ones, and the M_w/M_n values were narrow (～1.3), showing the typical features of “living”/controlled radical polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Samarium(III)-based AGET ATRP of Acrylonitrile Using Ascorbic Acid as Reducing Agent

Atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) initiated by ethyl 2-bromoisobutyrate (EBiB) was approached for the first time in the absence of oxygen and in the presence of air, using a novel catalyst system based on SmBr₃·6H₂O/isophthalic acid complexes and using ascorbic acid (VC) as a reducing agent. Both the polymerization in the absence of oxygen and in the presence of air proceeded in a well-controlled manner as evidenced by kinetic studies. Compared with the polymerization in the absence of oxygen, the polymerization in the presence of air provided rather slow reaction rate and showed better control of molecular weight and its distribution under the same experimental conditions. The polymerization apparent activation energies in the absence of oxygen and in the presence of air were calculated to be 47.1 and 51.3 kJ·mol^?1, respectively. A slow polymerization rate and a broad polydispersity index were observed using anisole and toluene instead of DMF as solvent. Polyacrylonitrile obtained was successfully used as a macroinitiator to proceed the chain extension polymerization of styrene via AGET ATRP in the presence of air.     

AGET ATRP of methyl methacrylate with poly(ethylene glycol) (PEG) as solvent and TMEDA as both ligand and reducing agent

Activator generated by electron transfer atom transfer radical polymerization of methyl methacrylate (MMA) in inexpensive, non-toxic poly(ethylene glycol) (PEG), with air-stable Cu(II)X₂(X = Br, Cl) as the catalyst and N,N,N′,N′-tetramethylethylenediamine (TMEDA) as both ligand and reducing agent was investigated. The polymerizations in PEG proceeded in a well-controlled manner as evidenced by kinetic studies and chain extension results. The polydispersity of the polymer obtained was quite narrow, with a weight-average molecular weight/number-average molecular weight ratio of less than 1.2. Effects of the TMEDA content and the catalysts on polymerization were also investigated, respectively.     

Iron-mediated AGET ATRP of styrene and methyl methacrylate using ascorbic acid sodium salt as reducing agent

Atom transfer radical polymerization of styrene(St) and methyl methacrylate(MMA) in bulk and in different solvents using activators generated by electron transfer(AGET ATRP) were investigated in the presence of a limited amount of air using FeCl3·6H2O as the catalyst, ascorbic acid sodium salt(AsAc-Na) as the reducing agent, and a cheap and commercially available tetrabutylammonium bromide(TBABr) as the ligand. It was found that polymerization in THF resulted in shorter induction period than that in bulk and in toluene for AGET ATRP of St, while referring to AGET ATRP of MMA, polymerization in THF showed three advantages compared with that in bulk and toluene: 1) shortening the induction period, 2) enhancing the polymerization rate and 3) having better controllability. The living features of the obtained polymers were verified by chain end analysis and chain-extension experiments.     

Air‐tolerantly surface‐initiated AGET ATRP mediated by iron catalyst from silica nanoparticles

Well‐defined polymer‐nanoparticle hybrids were prepared by a newly reported method: atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) mediated by iron catalyst. The kinetics of the surface‐initiated AGET ATRP of methyl methacrylate from the silica nanoparticles, which was mediated by FeCl₃/triphenylphosphine as a catalyst complex, ascorbic acid as a reducing agent, N,N‐dimethylformamide as the solvent in the presence of a “sacrificial” (free) initiator, was studied. Both the free and grafted polymers were grown in a control manner. The chemical composition of the nanocomposites was characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. Thermogravimetric analysis was used to estimate the content of the grafted organic compound, and transmission electron micrographs was used to observe the core‐shell structure of the hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2006–2015, 2010     

ARGET ATRP of acrylonitrile with ionic liquid as reaction media and 1,1,4,7,7‐pentamethyldiethylenetriamine as both ligand and reducing agent in the presence of air

[C₁₂mim][BF₄], [C₈mim][BF₄], and [C₄mim][BF₄] were first applied as reaction media for atom transfer radical polymerization using activators regenerated by electron transfer (ARGET ATRP) of acrylonitrile (AN) with 1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) as both ligand and reducing agent in the presence of air. The rate of polymerization in [C₁₂mim][BF₄] was considerably faster than in [C₈mim][BF₄] and [C₄mim][BF₄]. ARGET ATRP of AN in [C₁₂mim][BF₄] were better controlled than in [C₈mim][BF₄] and [C₄mim][BF₄] under the same experimental conditions. With an increase in the content of PMDETA, the polymerization provided an accelerated reaction rate and a broader polymer molecular weight distribution. A slow polymerization rate and a broad polydispersity index were observed using TMEDA instead of PMDETA as both ligand and reducing agent. There was an obvious induction period with CuCl₂ instead of CuBr₂ as catalyst. Well‐defined PAN‐b‐PMMA with higher molecular weight at 104,560 and relatively broader distribution at 1.35 was successfully prepared with PAN as macroinitiator via ARGET ATRP in [C₁₂mim][BF₄] in the presence of air. The resultant fibers were obtained with the fineness at 1.17dtex and the tenacity at 6.03cN · dtex^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

Atom transfer radical polymerization using activators regenerated by electron transfer of acrylonitrile in 1‐(1‐ethoxycarbonylethyl)‐3‐methylimidazolium hexafluorophospate

Atom transfer radical polymerization using activators regenerated by electron transfer (ARGET ATRP) of acrylonitrile (AN) was first approached with 1‐(1‐ethoxycarbonylethyl)‐3‐methylimidazolium tetrafluoroborate ([ecemim][BF₄]) as reaction medium and tin(II) bis(2‐ethylhexanoate) (Sn(EH)₂) as reducing agent in the presence of air. When compared with in bulk, an obvious increase of polymer isotacticity was observed for ARGET ATRP of AN in 1‐(1‐ethoxycarbonylethyl)‐3‐methylimidazolium hexafluorophospate ([ecemim][PF₆]), the reaction rate of ARGET ATRP of AN in [ecemim][PF₆] was higher and the polymerization process was better controlled. The block copolymer polyacrylonitrile‐block‐poly(methyl methacrylate) with molecular weight at 69,750, distribution at 1.34, and isotacticity at 0.36 was successfully obtained in [ecemim][PF₆]. [Ecemim][PF₆] and the catalyst system were recycled and reused and had no effect on the living nature of polymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Alumina additives for fast iron‐mediated AGET ATRP of MMA using onium salt as ligand

Three kinds of alumina (acidic, neutral, and basic Al₂O₃) were effective as additives for the control and rate enhancement of iron‐mediated AGET (activators generated by electron transfer) ATRP (atom transfer radical polymerization) of methyl methacrylate (MMA) in the presence of limited amount of air, using FeCl₃·6H₂O as the catalyst, tetrabutylammonium bromide or tetra‐n‐butylphosphonium bromide as the ligand, ethyl 2‐bromoisobutyrate as the initiator, and ascorbic acid as the reducing agent. The conversion could be up to 83.9% in the case of basic Al₂O₃ and 75.3% with neutral Al₂O₃ only in 13 h, respectively, whereas no polymer could be obtained even in 50 h without additives. The polymers obtained with neutral and basic Al₂O₃ had controlled molecular weights and low M_w/M_n values (～1.2). Tacticities of the as‐prepared PMMA in the presence of these three kinds of Al₂O₃ were consistent with that obtained from conventional free‐radical polymerization of MMA. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Reverse ATRP process of acrylonitrile in the presence of ionic liquids

An ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([C₄mim] [BF₄]), was first used as the solvent in azobisisobutyronitrile (AIBN)‐initiated reverse atom transfer radical polymerization (RATRP) of acrylonitrile with FeCl₃/succinic acid (SA) as the catalyst system. The polymerization in [C₄mim][BF₄] proceeded in a well‐controlled manner as evidenced by kinetic studies. Compared with the polymerization in bulk, the polymerization in [C₄mim][BF₄] not only showed the best control of molecular weight and its distribution but also provided rather rapid reaction rate with the ratio of [C₄mim][BF₄] at 200:1:2:4. The polymerization apparent activation energies in [C₄mim][BF₄] and bulk were calculated to be 48.2 and 55.7 kJ mol^?1, respectively. Polyacrylonitrile obtained was successfully used as a macroinitiator to proceed the chain extension polymerization in [C₄mim][BF₄] via a conventional ATRP process. [C₄mim][BF₄] and the catalyst system could be easily recycled and reused after simple purification and had no effect on the living nature of polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2701–2707, 2008     

AGET ATRP of water‐soluble PEGMA: Fast living radical polymerization mediated by iron catalyst

In this work, living radical polymerizations of a water‐soluble monomer poly(ethylene glycol) monomethyl ether methacylate (PEGMA) in bulk with low‐toxic iron catalyst system, including iron chloride hexahydrate and triphenylphosphine, were carried out successfully. Effect of reaction temperature and catalyst concentration on the polymerization of PEGMA was investigated. The polymerization kinetics showed the features of “living”/controlled radical polymerization. For example, M_n,GPC values of the resultant polymers increased linearly with monomer conversion. A faster polymerization of PEGMA could be obtained in the presence of a reducing agent Fe(0) wire or ascorbic acid. In the case of Fe(0) wire as the reducing agent, a monomer conversion of 80% was obtained in 80 min of reaction time at 90 °C, yielding a water‐soluble poly(PEGMA) with M_n = 65,500 g mol^?1 and M_w/M_n = 1.39. The features of “living”/controlled radical polymerization of PEGMA were verified by analysis of chain‐end and chain‐extension experiments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A Highly Active Iron‐Based Catalyst System for the AGET ATRP of Styrene

The atom transfer radical polymerization of styrene using activators generated by electron transfer (AGET ATRP) has been carried out in bulk in a limited amount of air at 110 °C, using 1,3,5‐(2′‐bromo‐2′‐methylpropionato)benzene (BMPB) as an initiator and FeCl₃ · 6H₂O/tris(3,6‐dioxaheptyl) amine (TDA‐1)/ascorbic acid (VC) as a novel Fe^III‐mediated catalyst system. The results of the polymerizations demonstrate the features of ‘living’/controlled free‐radical polymerization, such as the number‐average molecular weights being close to their corresponding theoretical values and increasing linearly with monomer conversion, and narrow molecular weight distributions ( = 1.18–1.26). The end functionality of the obtained polymers was confirmed by ¹H and ¹³C NMR spectra as well as a chain‐extension reaction.

     

Iron‐mediated AGET ATRP of MMA with sulfosalicylic acid as a ligand

Iron‐mediated atom transfer radical polymerizations with activators generated by electron transfer of methyl methacrylate in N,N‐dimethylformamide solution in the presence and absence of a limited amount of air, using FeCl₃·6H₂O as the catalyst, ethyl 2‐bromoisobutyrate (EBiB) as the initiator, vitamin C as the reducing agent, and a commercially available organic acid, sulfosalicylic acid (SSA), as the ligand were investigated. Addition of SSA as the ligand could enhance the polymerization rate, and produce poly(methyl methacrylate) with controllable molecular weights and narrow molecular weight distributions (M_w/M_n = 1.30–1.50). The effect of [FeCl₃·6H₂O]₀/[SSA]₀ on the polymerization was studied by cyclic voltammetry characterization. Chain extension was performed to confirm the “living”/controlled nature of the polymerization system. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Triphenylphosphine as reducing agent for copper(II)-catalyzed AGET ATRP

Triphenylphosphine(TPP) was used as reducing agent to continuously generate the Cu(I) activator in copper(II)-catalyzed activators generated by electron transfer atom transfer radical polymerization(AGET ATRP). For example, the polymers prepared with a molar ratio of [MMA]0/[EBi B]0/[Cu Cl2]0/[PMDETA]0/[TPP]0 = 500/1/0.1/0.5/0.5 had controlled molecular weights and low molecular weight distribution(Mw/Mn) values(~1.2). TPP as a commercial reducing agent provides a convenient copper-catalyzed AGET ATRP procedure for the preparation of well-defined polymers.     

AGET ATRP in the Presence of Air in Miniemulsion and in Bulk

Summary: The recently developed initiation system, activators generated by electron transfer (AGET), is used in atom transfer radical polymerization (ATRP) in the presence of a limited amount of air. Ascorbic acid and tin(II ) 2‐ethylhexanoate are used as reducing agents in miniemulsion and bulk, respectively. An excess of reducing agent consumes the oxygen present in the system and, therefore, provides a deoxygenated environment for ATRP. ATRP of butyl acrylate is successfully carried out in miniemulsion and in the presence of air. During polymerization the radical concentration remains constant. The polymerization reaches over 60% monomer conversion after 6 h, which results in polymers with a predetermined molecular weight = 14 000 g · mol⁻¹ and a low polydispersity ( = 1.23). AGET ATRP of styrene is also successful in bulk in the presence of air, as evidenced by linear semi‐logarithmic kinetics, which leads to polystyrene with an of 13 400 g · mol⁻¹ and a low polydispersity index ( = 1.14).

Appearance of miniemulsion before and after the reducing agent ascorbic acid was added (left); and GPC traces representing molecular weights during the AGET ATRP of BA in miniemulsion in the presence of air (right).     

Synthesis of poly(n‐butyl acrylate) homopolymer and poly(styrene‐b‐n‐butyl acrylate‐b‐styrene) triblock copolymer via AGET emulsion ATRP using a cationic surfactant

Cationic emulsions of triblock copolymer particles comprising a poly(n‐butyl acrylate) (PⁿBA) central block and polystyrene (PS) outer blocks were synthesized by activator generated by electron transfer (AGET) atom transfer radical polymerization (ATRP). Difunctional ATRP initiator, ethylene bis(2‐bromoisobutyrate) (EBBiB), was used as initiator to synthesize the ABA type poly(styrene‐b‐n‐butyl acrylate‐b‐styrene) (PS‐PⁿBA‐PS) triblock copolymer. The effects of ligand and cationic surfactant on polymerizations were also discussed. Gel permeation chromatography (GPC) was used to characterize the molecular weight (M_n) and molecular weight distribution (MWD) of the resultant triblock copolymers. Particle size and particle size distribution of resulted latexes were characterized by dynamic light scattering (DLS). The resultant latexes showed good colloidal stability with average particle size around 100–300 nm in diameter. Glass transition temperature (T_g) of copolymers was studied by differential scanning calorimetry (DSC). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 611–620     

Rate‐enhanced ATRP in the presence of catalytic amounts of base: An example of iron‐mediated AGET ATRP of MMA

The catalytic amount of inorganic bases (i.e., NaOH, Na₃PO₄, NaHCO₃, and Na₂CO₃) and organic bases such as pyridine and triethylamine was used as the additives in an iron‐mediated atom transfer radical polymerization with activators generated by electron transfer (AGET ATRP) of a polar monomer methyl methacrylate (MMA) using FeCl₃·6H₂O as the catalyst, ethyl 2‐bromoisobutyrate (EBiB) as the initiator, ascorbic acid (AsAc) as the reducing agent, and tetrabutylammonium bromide (TBABr) as the ligand. All these bases can result in dual enhancement of polymerization rate and controllability over molecular weight while keeping low M_w/M_n values (<1.3) for the resultant polymers. For example, the polymerization rate of AGET ATRP with a molar ratio of [MMA]₀/[EBiB]₀/[FeCl₃·6H₂O]₀/[TBABr]₀/[AsAc]₀/[NaOH]₀ = 500/1/1/2/2/1.5 using NaOH as the additives was more than two times of that without NaOH. The nature of “living”/controlled free radical polymerization in the presence of base was confirmed by chain‐extension experiments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Iron‐Mediated ICAR ATRP of Styrene and Methyl Methacrylate in the Absence of Thermal Radical Initiator

Initiators for continuous activator regeneration in atom transfer radical polymerization (ICAR ATRP) is a new technique for conducting ATRP. ICAR ATRP has many strong advantages over normal ATRP, such as forming the reductive transition metal species in situ using oxidatively stable transition metal species and a lower amount of metal catalyst in comparison with the normal ATRP system. In this work, the iron‐mediated ICAR ATRP of styrene and methyl methacrylate are reported for the first time using oxidatively stable FeCl₃ · 6H₂O as the catalyst in the absence of any thermal radical initiator. The kinetics of the polymerizations and effect of different polymerization conditions are studied. It is found that the polymerization of styrene can be conducted well even if the amount of iron(III ) is as low as 50 ppm.