Activators Regenerated By Electron Transfer Atom Transfer Radical Polymerization Research Articles

RETRACTED: An imprinted Ag@CdS core shell nanoparticle based optical-electrochemical dual probe for trace level recognition of ferritin

In this work, we present a new approach to prepare the Ag@CdS core-shell fluorescent nanoparticles wrapped with molecularly imprinted polymer for ferritin macromolecule by capping with vinyl derivative of cysteine. The imprinted Ag@CdS nanoparticle was prepared via activator regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP) method onto the surface of vinyl silane modified pencil graphite electrode. Combination of Ag and CdS in a single motif causes the dual behavior of core shell nanoparticle, which shows enhanced fluorescence as well as electrochemical properties. The performance of the obtained imprinted sensor was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, chronocoulometry, differential pulse voltammetry and fluorescence spectrophotometry. Under the optimal experimental conditions, the current response of the electrochemical sensor was linear to ferritin concentrations in the range from 1.99 to 23.43 µg L⁻¹, with the detection limit of 0.65 µg L⁻¹. Similarly, a linear response was obtained between fluorescence quenching of imprinted Ag@CdS and concentration of ferritin in the range from 4.0 to 91.0 µg L⁻¹, with limit of detection (LOD) of 1.3 µg L⁻¹. The method was successfully applied to the analysis of blood serum samples of five different men and women with acceptable recoveries of 99.7% and 100.3% (RSD in %=1.0-2.0).

Controlled synthesis and characterization of core-shell fluoro-silicone-containing fabric agent

The core-shell particles containing fluorine-silicon polymer was prepared by activators regenerated by electron transfer atom transfer radical polymerization(ARGET-ATRP)using SiO2-Br as initiator.The obtained polymer with well-controlled molecular weight and low polydispersity was used as water and oil repellent fabric finishing agent.Kinetics of the polymerization showed the polymerization was a living/controlled system.Characterization of FT-IR,1 H NMR,19 F NMR,XPS,TEM confirmed the core-shell structure of the polymer and the presence of F element.The formation of dual micro-nano structure between nano polymer and the surface of fabric enhanced the water and oil repellency of the cotton fabric.

Nitroxide polymer brushes prepared by surface-initiated ARGET ATRP and their selective oxidation performances

Polymer brushes with 2,2,6,6-tetramethyl-4-piperidyl methacrylate (TMPM) units, grafted on the cross-linked polystyrene (PS) microspheres, were synthesized via surface-initiated ARGET (activators regenerated by electron transfer) ATRP (atom transfer radical polymerization). They were further oxidized to yield nitroxide polymer brushes containing nitroxide radical units (TEMPO). The obtained polymer brushes were characterized by Fourier transform infrared spec- troscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron spin resonance (ESR) and gel permeation chromatography (GPC). The catalytic properties of nitroxide polymer brushes for selective oxi- dation of benzyl alcohol were investigated. The results showed that the performances were good and the yield was up to 96%. Furthermore, the block brush had similar catalyst properties to non-supported TEMPO in terms of activity and selec- tivity. It could be recovered by centrifugation. The unity of high catalyst property and easy recovery was achieved.

Functional amphiphilic oligo(ethylene oxide) methacrylate‐based block copolymers: synthesis by an activator regenerated by electron transfer process for atom transfer radical polymerization and aqueous micellization

AbstractWell‐defined amphiphilic block copolymers (ABPs) consisting of poly(oligo(ethylene oxide) monomethyl ether methacrylate) (POEOMA) and poly(tert‐butyl methacrylate) (PtBMA) were successfully synthesized using an activator regenerated by electron transfer (ARGET) process for atom transfer radical polymerization (ATRP). Two synthetic routes starting from the synthesis of either PtBMA or POEOMA macroinitiators followed by chain extension with the alternate monomer were examined. The results from a kinetic investigation suggest that both ARGET ATRP of OEOMA and subsequent chain extension with tBMA proceed in a living manner, yielding functional POEOMA‐block‐PtBMA ABPs in the presence of various functional initiators. As a preliminary evaluation for a polymer‐based drug delivery system, the functional ABPs were examined for aqueous micellization through self‐assembly that allows for the preparation of colloidally stable micellar aggregates with various corona morphologies. For flower‐like micelles bearing disulfide linkages in the center of hydrophilic loops, the reductive cleavage of the disulfide linkages enables a facile conversion to thiol‐decorated micelles without a measurable change in particle size. © 2013 Society of Chemical Industry

Activators regenerated by electron transfer in ATRP of methyl methacrylate with alcohol as reducing agent in the presence of a base

Poly(methyl methacrylate) (PMMA) was synthesized via activators regenerated by electron transfer (ARGET) in atom transfer radical polymerization (ATRP) (ARGET ATRP) of methyl methacrylate in N,N-dimethylformamide and using ethyl 2-bromoisobutyrate as initiator, CuCl2 as catalyst, N,N,N′,N′-tetramethylethylene-diamine as ligand and ethanol as a reducing agent. The polymerization temperature was kept at 70 °C. A well-defined PMMA with predetermined molecular weight and narrow molecular weight distribution was obtained. A linear relationship between ln([M]0/[M]) and polymerization time was found to show the living and controllable radical polymerization. The molecular weights of the obtained polymers increased linearly with monomer conversion and the data are in good agreement with the theoretical values with narrow molecular weight distribution (M w/M n). That is to say, alcohols were found to be a kind of highly efficient agents in the presence of Na2CO3 in this system. The effects of temperature, different types of alcohols and the amount of n-propanol on the polymerization were investigated. With increasing temperature (changed from 70 to 90 °C) and the amount of n-propanol (changed from 500:1:1:2:1:2 to 500:1:1:2:10:2), the conversion increased from 15.6 to 34.7 % and from 8.6 to 26.8 %, respectively. However, the value of M w/M n became broader when the molar ratio of [MMA]0/[EBiB]0/[CuCl2]0/[TMEDA]0/[n-propanol]0/[Na2CO3]0 was 500:1:1:2:1:2, indicating that the amount of n-propanol played an important role in ARGET ATRP of MMA. The activation energy was calculated to be 51.96 kJ/mol. The different types of alcohol were demonstrated to be an efficient reducing agent in this system except for tert-butyl alcohol. The “living” feature of the obtained polymer was further verified by a chain extension experiment. The obtained polymer was characterized by 1H NMR and GPC.

Protein–polymer hybrids: Conducting ARGET ATRP from a genetically encoded cleavable ATRP initiator

Protein–polymer hybrids are an important class of biomaterials. Described is the preparation of a genetically incorporated a non-canonical amino acid (nCAA) containing an ester linked atom transfer radical polymerization (ATRP) initiator, followed by a controlled “grafting from” polymerization. A Methanococcus jannaschii tyrosyl-tRNA synthetase/tRNACUA pair was selected to genetically encode p-bromoisobutyryloxymethyl-l-phenylalanine (biF) in response to an amber codon. This biF was directly incorporated into green fluorescent protein (GFP) at residue 134 generating biF-GFP. Activators regenerated by electron transfer (ARGET) ATRP was conducted under biologically relevant conditions to graft well-defined poly(oligo ethylene oxide methacrylate) from the biF-GFP. The biF-GFP retained its biofluorescence properties throughout the polymerization indicating the utility of ARGET ATRP for preparing protein–polymer hybrids. The presence of a base-labile ester bond in the initiator, allowed cleavage of the grafted polymer from the protein and directly analyze their molecular weight and molecular weight distribution using gel permeation chromatography (GPC). The cleaved final polymer had a Mn=27,000 and a molecular weight distribution of Mw/Mn=1.27.

Synthesis of PMMA-b-PU-b-PMMA tri-block copolymers through ARGET ATRP in the presence of air

ARGET (activators regenerated by electron transfer) ATRP (atom transfer radical polymerization) has been suc- cessfully performed (in flasks fitted with rubber septa without the need for use of Schlenk line) in the presence of limited amount of air and with a very small (370 ppm) amount of copper catalyst together with an appropriate reducing agent Cu(0). Novelty of this work is that the poly(methyl methacrylate)-block-polyurethane-block-poly(methyl methacrylate) tri- block copolymers were synthesized for the first time through ARGET ATRP, by using tertiary bromine-terminated polyurethane as a macroinitiator (MBP-PU-MBP), CuBr2 or CuCl2 as a catalyst and N,N,N,N#,N#-pentamethyldiethylene- triamine (PMDETA) or 2,2-bipyridine (Bpy) as a complexing agent. As the polymerization time increases, both the monomer conversion and ln((M)0/(M)) increased and the molecular weight of copolymer increases linearly with increasing conversion. Theoretical number-average molecular weight (Mn, th) of the tri-block copolymers was found to be comparable with number-average molecular weight determined by GPC analyses (Mn, GPC). These results indicate that the formation of the tri-block copolymers was through atom transfer radical polymerization mechanism. 1 H and 13 C NMR spectral methods were employed to confirm chemical structures of synthesized macroinitiator and tri-block copolymers. Mole percentage of PMMA in the tri-block copolymers was calculated using 1 H NMR spectroscopy and was found to be comparable with the GPC results. Additionally, the studies of surface properties (confocal microscopy and SFE) of tri-block copolymer coatings confirmed the presence of MMA segments.

Specific Binding of Immunoglobulin G with Bioactive Short Peptides Supported on Antifouling Copolymer Layers for Detection in Quartz Crystal Microgravimetry and Surface Plasmon Resonance

A new peptide-based system supported on copolymer brushes grafted from gold sensors and with resistance to nonspecific adsorption is reported for selective binding of human immunoglobulin G (IgG). A random copolymer rich in primary amines, poly(2-aminoethyl methacrylate hydrochloride-co-2-hydroxyethyl methacrylate) (poly(AMA-co-HEMA)) was first grafted from initiator-coated gold substrates via activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP), followed by immobilization of acetylated-HWRGWVA peptide, which has specific binding affinity with IgG. The peptide ligands covalently linked to the soft copolymer layer were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle, ellipsometry, and atomic force microscopy (AFM). The extent of binding, binding affinity, and selectivity for target IgG molecules as well as the capability to minimize nonspecific interactions with other proteins were examined by fluorescence imaging, surface plasmon resonance (SPR), and quartz crystal microgravimetry (QCM). The effect of copolymer molecular composition and analyte concentration was elucidated in order to design systems based on immobilized peptides for high signal-to-noise response and detection limits that meet the requirements for IgG biosensing in fluid matrixes.

Fe‐mediated ARGET atom transfer radical polymerization of methyl methacrylate in ionic liquid‐based microemulsion

AbstractPoly(methyl methacrylate) (PMMA) was synthesized by activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) of MMA in ionic liquid‐based microemulsion with polyoxyethylene sorbitan monooleate (Tween 80) as surfactant. The polymerization was carried out at 25°C with CCl4 as initiator, FeCl3·6H2O/N,N,N′,N′‐tetramethyl‐1,2‐ethanediamine (TMEDA) as catalyst complex in the presence of reducing agent ascorbic acid (VC). The polymerization kinetics showed the feature of controlled/″living″ process as evidenced by a linear first‐order plot. The well‐controlled polymers were obtained with narrow polydispersity indices and the ionic liquid‐based microemulsions were transparent with a particle size less than 30 nm. The obtained polymer was characterized by 1H NMR and gel permeation chromatography. The chain extension was successfully achieved by the obtained PMMA macroinitiator/FeCl3·6H2O/TMEDA/VC initiator system based on ARGET ATRP method. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Polystyrene–organoclay nanocomposites produced by in situ activators regenerated by electron transfer for atom transfer radical polymerization

Abstract A newly developed initiation system, activators regenerated by electron transfer (ARGET), was employed to synthesize polystyrene-organoclay nanocomposites via atom transfer radical polymerization (ATRP). ARGET ATRP was applied since it is carried out at significantly low concentrations of the catalyst and environmentally acceptable reducing agents. Conversion and molecular weight evaluations were performed using gravimetry and size exclusion chromatography (SEC), respectively. According to the findings, addition of clay content resulted in a decrease in conversion and molecular weight of nanocomposites. However, an increase of polydispersity index is observed by increasing nanoclay loading. The living nature of the polymerization is revealed by 1H NMR spectroscopy and extracted data from the SEC traces. X-ray diffraction (XRD) analysis shows that organoclay layers are disordered and delaminated in the polymer matrix and exfoliated morphology is obtained. Thermogravimetric analysis (TGA) shows that thermal stability of the nanocomposites is higher than the neat polystyrene. A decrease in glass transition temperature of the samples by increasing organoclay content is observed by differential scanning calorimetry (DSC). Transmission electron microscopy (TEM) reveals that clay layers are partially exfoliated in the polymer matrix containing 2 wt% of organomodified montmorillonite (PSON 2) and a dispersion of partially exfoliated clay stacks is formed.

Formation of Polyampholyte Brushes via Controlled Radical Polymerization and Their Assembly in Solution

We describe the formation of polyampholytic block copolymer brushes and their assembly in solution. Specifically, we employ "surface-initiated" activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP) sequentially to form diblock copolymer grafts comprising blocks of poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) and poly(sodium methacrylate) (PNaMA) on flat impenetrable silica surfaces, i.e., SiO(x)/PNaMA-b-PDMAEMA and SiO(x)/PDMAEMA-b-PNaMA. Protonation of the PNaMA block results in formation of poly(methacrylic acid) (PMAA). We demonstrate that ARGET-ATRP of NaMA provides a convenient route to preparation of PMAA, which is an alternative method to the more traditional approach based on preparing PMAA by polymerizing tert-butyl methacrylate (tBMA) followed by cleavage of the tert-butyl group. We also discuss conformational changes of the individual polyelectrolyte blocks in solution as a function of solution pH by monitoring adsorption behavior of functionalized polystyrene spheres.

Polymer brushes on multiwalled carbon nanotubes by activators regenerated by electron transfer for atom transfer radical polymerization

AbstractThe synthesis and characterization of multiwalled carbon nanotube (MWCNT) polymer brushes produced by activators regenerated by electron transfer (ARGET) in atom‐transfer radical polymerization (ATRP) was discussed. The polymer brushes were synthesized by esterification of the MWCNT carboxylic acid groups with hydroxyethyl‐2‐bromoisobutyrate and subsequently used in ARGET ATRP. This created a well defined living polymer brush carbon nanotube of comparatively low polydispersity and a polymer layer 10 nm thick. As, ARGET ATRP uses only minute concentrations of copper (II) catalyst, and is less sensitive to air compared to other living polymerization techniques, this process is a more industry‐compatible route for the commercialization of such materials. The structural and chemical properties were explored by a range of techniques including high resolution transmission electron microscopy, gel permeation chromatography, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. In addition, the polymer brush nanotubes were explored for their potential use in films and as fillers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Hydrophobic Modification of Natural Cellulose Fiber with MMA via Surface-Initiated ARGET ATRP

To convert the hydrophilic cotton fiber into hydrophobic, grafting methyl methacrylate (MMA) on cotton fiber surface using ARGET (activators regenerated by electron transfer) ATRP (atom transfer radical polymerization) was studied in this paper. Four parallel experiments with different reaction time (2h/4h/6h/8h) were designed. The modified cotton fibers and the untreated control were examined using FTIR, SEM and contact angle analysis. The results show that as the reaction time prolonged, the peak of carbonyl stretching band of 2-bromoester at 1730cm-1 was stronger and the surface of cotton fiber was rougher, which demonstrates MMA has been grafted on the surface of cotton fiber successively and its amount increases with the reaction time. As the results of contact angle measurement, it shows that the hydrophilicity of cotton fiber can easily be modified by grafting of MMA, but the increasing amount of grafting chain had no obvious effects on further improving its hydrophobicity.

The synthesis of water‐soluble PHEMA via ARGET ATRP in protic media

Abstract2‐Hydroxyethyl methacrylate has been polymerized in methanol using activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP), to produce water‐soluble poly(2‐hydroxyethyl methacrylate) (PHEMA). The various parameters that determine control of the living polymerization have been explored. Using the Cu(II)/TPMA catalyst system (TPMA = tris(2‐pyridylmethyl)amine), controlled polymerization was achieved with Cu concentrations as low as 50 ppm relative to HEMA, with a [TPMA]/[Cu(II)] ratio of 5. Use of hydrazine as the reducing agent generally gave better control of polymerization than use of ascorbic acid. The polymerization conditions were tolerant of small amounts of air, and colorless polymers were easily isolated by simple precipitation and washing steps. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4084–4092, 2010

Reducing Copper Concentration in Polymers Prepared via Atom Transfer Radical Polymerization

AbstractThree different initiation systems for atom transfer radical polymerization (ATRP): normal ATRP, activators regenerated by electron transfer (ARGET) ATRP, and initiators for continuous activator regeneration (ICAR) ATRP were used to synthesize polystyrene with a number‐average molecular weight ≈20 000 g · mol−1. Each polymerization mixture was divided and subjected to one or more purification methods including passing through a column filled with neutral alumina, stirring with an ion exchange resin (ATRP Pure), or precipitation into hexanes or methanol. Inductively coupled mass spectrometry was used to analyze the concentration of copper in each sample. For the polystyrene prepared by normal ATRP, purification by a neutral alumina column was the most effective at removing copper (down to ≈2 parts per million by mass). For the ARGET and ICAR ATRP, purification by a neutral alumina column and stirring with 10 wt.‐% ATRP Pure gave comparable results (each ≈1 part per million by mass).magnified image

Grafting of polymer brushes from nanopore surface via atom transfer radical polymerization with activators regenerated by electron transfer

It is shown that atom transfer radical polymerization (ATRP) with activators regenerated by electron transfer (ARGET) is a powerful approach for grafting of polymer brushes from surfaces of high-surface-area nanoporous hosts, allowing one to achieve controlled polymer loadings and film thicknesses while maintaining the pore accessibility and moderate or high surface area. The approach was illustrated on SBA-15 silicas with cylindrical pores of diameter 22 and 14 nm as the nanoporous supports, and poly(methyl methacrylate) (PMMA) and polystyrene (PS) as the grafted polymers. The polymer loadings up to 36 wt.% and the grafted layer thicknesses of up to at least 2 nm were achieved in the polymerization process carried out in small vials without using a vacuum line. The specific surface areas of the obtained silica-polymer composites were 60–190 m2 g−1. The polymer chains exhibited quite low polydispersity (1.18–1.32) for polymer loadings up to 29 wt.%, while a higher polydispersity was observed for higher loadings, in which case the pores of the support were filled to a significant extent with the polymer graft. Due to its simplicity, ARGET ATRP emerges as a powerful and yet surprisingly straightforward way to synthesize well-defined polymer brushes in nanopores, opening a convenient avenue to a wide range of porous high-surface-area silica-polymer composites.

ARGET ATRP for Versatile Grafting of Cellulose Using Various Monomers

In recent years, cellulose-based materials have attracted significant attention. To broaden the application areas for cellulose, polymers are often grafted to/from the surface to modify its properties. This study applies ARGET (activators regenerated by electron transfer) ATRP (atom transfer radical polymerization) when straightforwardly grafting methyl methacrylate (MMA), styrene (St), and glycidyl methacrylate (GMA) from cellulose in the form of conventional filter paper in the presence of a sacrificial initiator. The free polymer, formed from the free initiator in parallel to the grafting, was characterized by (1)H NMR and SEC, showing that sufficient control is achieved. However, the analyses also indicated that the propagation from the surface cannot be neglected compared to the propagation of the free polymer at higher targeted molecular weights, which is an assumption often made. The grafted filter papers were evaluated with FT-IR, suggesting that the amount of polymer on the surface increased with increasing monomer conversion, which the FE-SEM micrographs of the substrates also demonstrated. Water contact angle (CA) measurements implied that covering layers of PMMA and PS were formed on the cellulose substrate, making the surface hydrophobic, in spite of low DPs. The CA of the PGMA-grafted filter papers revealed that, by utilizing either aprotic or protic solvents when washing the substrates, it was possible to either preserve or hydrolyze the epoxy groups. Independent of the solvent used, all grafted filter papers were essentially colorless after the washing procedure because of the low amount of copper required when performing ARGET ATRP. Nevertheless, surface modification of cellulose via ARGET ATRP truly facilitates the manufacturing since no thorough freeze-thaw degassing procedures are required.

Synthesis of high molecular weight 3-arm star PMMA by ARGET ATRP

High molecular weight (MW), 3-arm star poly(methyl methacrylate) (PMMA) with a narrow MW distribution (Mn=570,000 g/mol, PDI=1.36) was successfully synthesized by activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). The polymerization was carried out with a trifunctional initiator/CuBr2/N,N,N′,N′,N′-pentamethyldiethylenetriamine (PMDETA) initiator/catalyst system in the presence of a tin(II) 2-ethylhexanoate [Sn(EH)2] reducing agent at 90 °C. The concentration of the copper catalyst was as low as 30 ppm, and a high initiation efficiency of the initiating sites was obtained. The chain-end functionality of the high MW, 3-arm star PMMA was confirmed by a chain extension experiment with styrene via ARGET ATRP, using the same catalyst system.

Effect of Symmetry of Molecular Weight Distribution in Block Copolymers on Formation of “Metastable” Morphologies

Polystyrene-b-poly(methyl acrylate) (PS−PMA) copolymers were synthesized using activators regenerated by electron transfer (ARGET) for atom transfer radical polymerization (ATRP). Polydispersity of the PMA block was varied by adjusting the amount of copper catalyst in ARGET ATRP, and the resulting molecular weight distributions were found to be approximately symmetric. At a composition of 35 vol % of PMA, the formation of a hexagonally perforated lamellar (HPL) morphology was observed for a polydisperse PS−PMA copolymer for short- and long-term solvent-casting conditions. No order−order transitions were observed at elevated temperatures or after prolonged thermal annealing. The observed stabilization of the HPL morphology—that is considered to be metastable in narrow-disperse diblock copolymers as well as diblock copolymers with selective block polydispersity given by a Schulz−Zimm distribution—suggests that the skewness of the distribution of block molecular weights is an important parameter for the stru...

Tripodal imidazole containing ligands for copper catalyzed ATRP

AbstractTripodal imidazole containing ligands, bis((2‐pyridyl)methyl)(1‐methylimidazole‐2‐yl)methyl)amine (BPIA) and bis(1‐methylimidazole‐2‐yl)methyl)((2‐pyridyl)methyl)amine (BIPA), were synthesized and used for copper catalyzed atom transfer radical polymerization (ATRP) of n‐butyl acrylate (nBA). The molecular weights of poly(n‐butyl acrylate) (PnBA) catalyzed by CuBr/BPIA and CuBr/BIPA complexes increased linearly with nBA conversions and they were close to theoretical values with low polydispersities. ATRP equilibrium rate constant (KATRP) measurements showed that bothCuBr/BPIA and CuBr/BIPA complexes had high KATRP values, similar to that of CuBr/tri(2‐pyridylmethyl)amine (TPMA), which is one of the ATRP most active ligands. Activators regenerated by electron transfer (ARGET) ATRP of nBA with CuBr2/BPIA and CuBr2/BIPA complexes were also conducted and polymerization reached high nBA conversions, resulting in PnBA with low polydispersities. This suggests that the copper complexes with BPIA and BIPA were sufficiently stable and active to conduct ATRP when catalyst concentration was low. ARGET ATRP to form high molecular weight PnBA with CuBr2/BPIA and CuBr2/BIPA complexes was also successful. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2015–2024, 2008