Electron Transfer Atom Transfer Radical Polymerization Research Articles

Precise Regulation in Chain-Edge Structural Microenvironments of 1D Covalent Organic Frameworks for Photocatalysis.

Covalent organic frameworks (COFs) constitute a promising research topic for photocatalytic reactions, but the rules and conformational relationships of 1D COFs are poorly defined. Herein, the chain edge structure is designed by precise modulation at the atomic level, and the 1D COFs bonded by C, O, and S elements is directionally prepared for oxygen-tolerant photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) reactions. It is demonstrated that heteroatom-type chain edge structures (─O─, ─S─) lead to a decrease in intra-plane conjugation, which restricts the effective transport of photogenerated electrons along the direction of the 1D strip. In contrast, the all-carbon type chain edge structure (─C─) with higher intra-plane conjugation not only reduces the energy loss of photoexcited electrons but also enhances the carrier density, which exhibits the optimal photopolymerization performance. This work offers valuable guidance in the exploitation of 1D COFs for high photocatalytic performance. This work offers valuable guidance in the exploitation of 1D COFs for high photocatalytic performance.

Copper Nanodrugs by Atom Transfer Radical Polymerization

In this study, some copper catalysts used for atom transfer radical polymerization (ATRP) were explored as efficient anti‐tumor agents. The aqueous solution of copper‐containing nanoparticles with uniform spheric morphology was in situ prepared through a copper‐catalyzed activator generated by electron transfer (AGET) ATRP in water. Nanoparticles were then directly injected into tumor‐bearing mice for antitumor chemotherapy. The copper nanodrugs had prolonged blood circulation time and enhanced accumulation at tumor sites, thus showing potent antitumor activity. This work provides a novel strategy for precise and large‐scale preparation of copper nanodrugs with high antitumor activity.

Copper Nanodrugs by Atom Transfer Radical Polymerization.

In this study, some copper catalysts used for atom transfer radical polymerization (ATRP) were explored as efficient anti-tumor agents. The aqueous solution of copper-containing nanoparticles with uniform spheric morphology was in situ prepared through a copper-catalyzed activator generated by electron transfer (AGET) ATRP in water. Nanoparticles were then directly injected into tumor-bearing mice for antitumor chemotherapy. The copper nanodrugs had prolonged blood circulation time and enhanced accumulation at tumor sites, thus showing potent antitumor activity. This work provides a novel strategy for precise and large-scale preparation of copper nanodrugs with high antitumor activity.

A surface grafting strategy for antifouling/bioadhesive properties on a Janus-type polymeric thin film

There have been great technical challenges in preparation of a transparent polymeric thin film with Janus-type antifouling and bioadhesive properties on both surfaces, while maintaining the optical and mechanical characteristics of the bulk material. Herein, poly(2-hydroxyethyl methacrylate) (PHEMA), which is commonly used as an ophthalmic hydrogel, was employed as the bulk material for allowing consecutive surface grafting of functional polymer brushes, which eventually resulted in a Janus-type transparent thin film for potential biomedical implantation. First, a bromine-containing reagent served as the reactive initiator was silanized onto both surfaces of the PHEMA hydrogel thin film under a mild condition. Then, with the presence of selected physical shielding on one side using a scotch tape, polymer brushes with cell-adhesive Arg-Gly-Asp (RGD) peptide pendent groups were grafted from the other side of the PHEMA thin film, resulted in a highly improved cell attachment capability. Once the tape was removed and the RGD-modified surface was shielded, the zwitterionic polymer brushes comprising poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) segments were grafted on the surface, again through surface-initiated activators regenerated by electron transfer atom-transfer radical polymerization (SI-ARGET-ATRP). Hence, this side of the PHEMA film became super hydrophilic and exhibited antifouling properties on the surface. After the surface grafting modification, the whole PHEMA hydrogel maintained highly transparent and biocompatible for potential ophthalmic applications. This study provides a simple and rather universal strategy for fabricating Janus-type polymeric thin films with distinct biophysical/biochemical properties on both sides, which potentially applicable for the multifunctional requirements in biomedical applications.

Novel Copper-Based Catalytic Systems for Atom Transfer Radical Polymerization of Acrylonitrile

Atom Transfer Radical Polymerization (ATRP) is an effective catalytic process leading to well-defined polymers with desired properties. This process based on reversible deactivation of propagating chains has a lower rate in comparison with conventional radical polymerization, especially in the case of obtaining polymers with high molecular weights. Thus, the increase of the rate of this process with preserving control over molecular weight distribution is a challenging task. In this work, novel catalytic systems for Activators Generated by Electron Transfer (AGET) ATRP of acrylonitrile based on copper (II) bromide complexes were proposed. It was found that Rochelle salt (potassium sodium tartrate tetrahydrate) may be used as a reducing agent for regeneration of copper-based catalysts to increase the rate of the process. The provided UV-vis spectroscopy experiments have confirmed the reducing ability of tartaric anion. It was found that the use tandem catalytic system based on two copper complexes with different ligands also increases the polymerization rate. The performed experiments allowed us to develop a catalytic system for rapidly obtaining polyacrylonitrile polymers with desired molecular weights exceeding 100 kDa.

A specific sensor system based on in-situ synthesis fluorescent polymers by ARGET ATRP achieving sensitive exosome detection

Exosomes, as a kind of tumor biomarker, are often found at elevated levels above normal in the blood of cancer patients, making highly sensitive exosome testing important for monitoring the development and progression of cancer. In this work, an ultra-sensitive and specific fluorescence method for exosome assays was constructed on the basis of atom transfer radical polymerization (ATRP) technique. Firstly, two recognition units, the CD63 aptamer and the EGFR antibody, can specifically bind to exosomes to form a sandwich structure, which endows the proposed sensor with excellent selectivity through two specific recognitions. Secondly, activator regenerated by electron transfer ATRP (ARGET ATRP) polymerization amplification method can introduce a huge amount of the fluorescent monomers into the sensing system, leading to a marked rise in sensitivity. Under optimal experimental conditions, a clear linear relationship between the logarithm of the fluorescence intensity and the concentration of exosomes in the range of 5 × 104 exosomes/mL to 5 × 109 exosomes/mL was obtained. The limit of detection (LOD) was as low as 11,610 exosomes/mL. Furthermore, this sensor exhibited good selectivity and stability, and excellent immunity to interference, providing a new method for the detection of exosomes. The exosome detection strategy used in this system provides a new idea for effective detection of lung cancer at an early stage.

Selective Protein Conjugation of Poly(glycerol monomethacrylate) and Poly(polyethylene glycol methacrylate) with Tunable Topology via Reductive Amination with Multifunctional ATRP Initiators for Activity Preservation

In this study, we compare poly(glycerol monomethacrylate) (PGMA) of different chain lengths and architectures (linear and two-arm) with poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) as an alternative polymer platform for the synthesis of a new generation of protein–polymer conjugates. Mono- and two-arm functional atom-transfer radical polymerization (ATRP) initiators were designed and selectively attached to lysozyme at the N-terminus via reductive amination. Site-specific, grafting from activator regenerated by electron transfer (ARGET) ATRP was carried out in phosphate buffer, and the reaction parameters were optimized to obtain polymer conjugates with predetermined molar mass and topology. The activity preservation under proteolytic and high-temperature conditions showed a clear dependence on the structure of the repeating unit and on the macromolecular architecture. These results highlighted the potential of PGMA as a poly(ethylene glycol) (PEG) alternative for the half-life extension of biotherapeutics. Moreover, this synthetic approach may inspire the design of a new class of protein–polymer conjugates through an optimal combination of macromolecular composition and topology.

Novel Amphiphilic Polyfluorene-Graft-(Polymethacrylic Acid) Brushes: Synthesis, Conformation, and Self-Assembly.

Novel polyfluorene polymer brushes with polymethacrylic acid side chains were obtained by atom transfer radical polymerization (ATRP) and activator generated by electron transfer (AGET) ATRP of tert-butyl methacrylate on polyfluorene multifunctional macroinitiator, followed by protonolysis of the tert-butyl groups of the side chains. Kinetics of polymerization and molecular weights were fully characterized. These polymer brushes luminesce in the blue region of the spectrum with high quantum yields (0.64–0.77). It was shown that the luminescence intensity of polymer brushes is higher than the luminescence intensity of the macroinitiator (0.61). Moreover, due to their amphiphilic nature, they can form unimolecular micelles when an alcohol solution of the polymer brush is injected into water. These properties can potentially be used in drug delivery and bioimaging.

Facile preparation of antifouling nanofiltration membrane by grafting zwitterions for reuse of shale gas wastewater

Complex organic matter causes severe fouling when membranes are applied for shale gas wastewater (SGW) treatment. This study reports the grafting of a zwitterionic polymer brush consisting of poly (sulfobetaine methacrylate) (PSBMA) onto the surface of a commercial nanofiltration (NF) membrane via electron transfer-atom transfer radical polymerization (ARGET-ATRP) to achieve anti-fouling property, especially against organic foulants. Compared to the pristine NF membranes, the PSBMA-grafted NF membrane showed high performance when challenged by SGW as a feed stream: (1) The flux stability was significantly improved during long-term operation, with a 64.28% increase in flux normalization at 50% recovery rate of SGW, while maintaining a suitable initial flux and near constant ion removal rate; (2) Based on excitation-emission-matrix spectra integrated in the fluorescence region, the removal of protein-like organic matters and humus-like organic matters increased by 34% and 16.5%, respectively; (3) The XDLVO theory supports the hypothesis that the hydrophobic interactions between the membrane surface and organic foulants were reduced by enhancing the Lewis acid-base interaction energy. The proposed anti-fouling zwitterionic membranes has potential in industrial application for the on-site reuse of SGW.

Preparation of LCST regulable DES-lignin-g-PNVCL thermo-responsive polymer by ARGET-ATRP

To expand the field of high-value utilization of lignin. The degraded deep eutectic solvent lignin-grafted poly (N-Vinyl caprolactam) (DES-lignin-g-PNVCL) was synthesized by modified DES-lignin and NVCL via the combination of activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP). Fourier transform infrared spectroscopy (FT-IR), 1H NMR, X-ray electron spectroscopy (XPS), dynamic light scattering (DLS), differential scanning calorimeter (DSC) were used to characterize the structure and performance of DES-lignin-g-PNVCL. The results indicated that the PNVCL and DES-lignin-g-PNVCL were successfully prepared by ARGET-ATRP. The lowest critical solution temperature (LCST) of PNVCL was 35.75 °C. Due to different strength of hydrogen bond, different energies were required, so the LCST of the polymer can be regulated. When the molar ratio of phenolic hydroxyl group in degraded DES-lignin to 2-bromoisobutyryl bromide (BiBB) was increased from 1:1 to 1:7, the grafting rate of DES-lignin-Br was increased from 32.87% to 60.84%, and the LCST of DES-lignin-g-PNVCL was decreased from 47.98 °C to 27.88 °C. The LCST of DES-lignin-g-PNVCL was increased from 30.98 °C to 44.64 °C when the addition amount of DES-lignin-Br was increased from 20 mg to 200 mg. The LCST of DES-lignin-g-PNVCL was increased from 27.20 °C to 39.86 °C when the ratio of DMF/water was increased from 1:4 to 4:1. The LCST of DES-lignin-g-PNVCL was decreased from 52.10 °C to 31.02 °C when the concentration of DES-lignin-g-PNVCL was increased from 0.5 mg/mL to 2.5 mg/mL. The equation represented the relationship between LCST and influencing factors was obtained, the good predictability provided a tactics for preparing desired LCST thermo-responsible polymer.

Surface-Initiated, Catechol-Containing Polymer Films for Effective Chelation of Aluminum Ions.

We present a new route for obtaining surface-tethered polymer films containing pendant catechol functional groups via surface-initiated activators regenerated by electron-transfer atom-transfer radical polymerization (SI-ARGET ATRP) of glycidyl methacrylate (GMA) and post-polymerization modification of the resulting poly(glycidyl methacrylate) (pGMA) films with dopamine. This method enables a high degree of functionalization of pGMA films with catechol groups at a controlled level, depending on the duration of the post-polymerization modification reaction. The dopamine-pGMA films readily absorbs Al3+ and Zn2+ ions, as verified by quartz crystal microbalance with dissipation (QCM-D) under continuous flow conditions, and demonstrates a four-fold molar selectivity to Al3+ over Zn2+. The ions desorb from the films upon rinsing with pure deionized (DI) water, which regenerates the catechol sites in the dopamine-pGMA film. Subsequent exposure to metal ions after rinsing steps yields reproducible levels of loading.

Hydrogen Sulfide-Responsive Bicontinuous Nanospheres.

Block copolymers (BCPs) that can self-assemble into particles and be triggered by disease-specific molecules such as hydrogen sulfide (H2S) have the potential to impact on drug delivery, decreasing off-target toxicities while increasing drug efficacy. However, the incorporation of H2S-responsive aryl azides into BCPs for self-assembly has been limited by heat, light, and radical sensitivities. In this study, a robust activator regenerated by the electron-transfer atom-transfer radical polymerization reaction was used to synthesize aryl-azide-containing BCPs under ambient conditions. Conditions controlling self-assembly of the BCPs into 150-200 nm particles and the physicochemical properties of the particles were investigated. The use of nanoprecipitation with tetrahydrofuran to promote self-assembly of the BCPs resulted in vesicle structures, while dimethylformamide or dimethylsulfoxide resulted in polymeric bicontinuous nanospheres (BCNs). Triggering of the BCPs and particles (vesicles or BCNs) via exposure to H2S revealed that unsubstituted aryl azides were readily reduced (by HS-), resulting in particle disruption or cross-linking. The relative polar nature of the particle bilayers containing unsubstituted aryl azides and the open structure of the BCNs did however limit encapsulation of small hydrophilic and hydrophobic payloads. Incorporation of a benzylamide substituent onto the aryl azide group increased the hydrophobicity of the particles and encapsulation of hydrophilic cargo but reduced sensitivity to H2S, likely due to the reduced penetration of HS- into the bilayer.

Copper-catalyzed ARGET ATRP of styrene from ethyl α-haloisobutyrate in EtOAc/EtOH, using ascorbic acid/Na2CO3 as reducing system

Atom transfer radical polymerization (ATRP) is one of the most powerful techniques to synthesize precisely tailored polymers and macrostructures. Activators regenerated by electron transfer (ARGET) ATRP was developed as a “green” strategy to decrease the load of the metal catalyst. However, ARGET ATRP usually uses not-so-green reducing agents (e.g. Sn2+) or expensive and industrially impractical procedures. For these reasons, we report an ARGET ATRP of styrene with various carbonates as reducing agents, both alone and paired with ascorbic acid (AA), using monofunctional initiators and Cl or Br as exchanging atoms. The solvent mixture is composed of the green combination of EtOAc and EtOH, even in the presence of modest amounts of H2O. Cyclic voltammetry was used to evaluate the effect of H2O on the catalyst, as well as the absence of AA. The system returned high yields and low dispersities with low amounts of catalyst (~60 ppm) and moderate reaction times. Excellent results were obtained only with the Cl-ATRP system. NMR spectroscopy and kinetic analyses proved the livingness of the final polymer chains.

Green and sustainable method of manufacturing anti-fouling zwitterionic polymers-modified poly(vinyl chloride) ultrafiltration membranes

The nonsolvent induced phase separation (NIPS) method for ultrafiltration (UF) membrane fabrication relies on the extensive use of traditional solvents, thus ranking first in terms of ecological impacts among all the membrane fabrication steps. Methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (PolarClean), as a green solvent, was utilized in this study to fabricate poly(vinyl chloride) (PVC) UF membranes. Subsequently, in post-treatment process, zwitterionic polymer, [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (DMAPS), was grafted onto the membrane surface to enhance its anti-fouling properties using a greener surface-initiated activator regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP) reaction. This novel method used low toxicity chemicals, avoiding the environmental hazards of traditional ATRP, and greatly improving the reaction efficiency. We systematically studied the grafting time effect on the resulted membranes using sodium alginate as the foulant, and found that short grafting time (30 min) achieved excellent membrane performance: pure water permeability of 2872 L m−2 h−1 bar−1, flux recovery ratio of 86.4% after 7-hour fouling test, and foulant rejection of 96.0%. This work discusses for the first time the greener procedures with lower environmental impacts in both fabrication and modification processes of PVC UF membranes.

Kinetics of MMA Atom Transfer Radical Polymerization Initiated by Reducing Agent in Stirred Batch Emulsion Reactor

AbstractAb initio emulsion atom transfer radical polymerization (ATRP) differs from regular emulsion polymerization because the kinetic and thermodynamic aspects of each process are very unlikely alike. This paper presents a kinetic analysis of activator generated by electron transfer (AGET) ATRP of methyl methacrylate (MMA) in a stirred emulsion reactor. The focus of the study is to assess the variation of the monomer content in the organic phase and the rate polymerization for different reaction temperatures, as well as the impact of surfactant content and stirring speed on latex stability. Poly(methyl methacrylate) (PMMA) polymer samples are analyzed by means of gravimetry, dynamic light scattering, gel permeation chromatography, and HNMR techniques to determine monomer conversion, polymer particle diameter, molecular weight distribution, and polymer molecular structure, respectively. The results show the production of PMMA of narrow polydispersity index (Ð) and low molar mass (Mn) for MMA conversion around 60% and detect two‐regions instead of a three‐regions trend of rate of polymerization (Rp) as conventional emulsion polymerization. The reaction rate increases during the nucleation stage and then flattens over an invariant trend which confirms a living feature of the AGET ATRP polymerization. The average number of radicals per latex particle (ñ) is also debated.

Membrane Biofouling Control by Surface Modification of Quaternary Ammonium Compound Using Atom-Transfer Radical-Polymerization Method with Silica Nanoparticle as Interlayer.

A facile approach to fabricate antibiofouling membrane was developed by grafting quaternary ammonium compounds (QACs) onto polyvinylidene fluoride (PVDF) membrane via surface-initiated activators regenerated by electron transfer atom-transfer radical-polymerization (ARGET ATRP) method. During the modification process, a hydrophilic silica nanoparticle layer was also immobilized onto the membrane surface as an interlayer through silicification reaction for QAC grafting, which imparted the membrane with favorable surface properties (e.g., hydrophilic and negatively charged surface). The QAC-modified membrane (MQ) showed significantly improved hydrophilicity and permeability mainly due to the introduction of silica nanoparticles and exposure of hydrophilic quaternary ammonium groups instead of long alkyl chains. Furthermore, the coverage of QAC onto membrane surface enabled MQ membrane to have clear antibacterial effect, with an inhibition rate ~99.9% of Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), respectively. According to the batch filtration test, MQ had better antibiofouling performance compared to the control membrane, which was ascribed to enhanced hydrophilicity and antibacterial activity. Furthermore, the MQ membrane also exhibited impressive stability of QAC upon suffering repeated fouling–cleaning tests. The modification protocols provide a new robust way to fabricate high-performance antibiofouling QAC-based membranes for wastewater treatment.

Valorization of organosolv lignin: Architectural strategy to enhance mechanical strength and UV protection in self-healing polymers

Altering the architecture of conventional self-healing polymers, from the original linear to a multiple-branched structure, has proved to be efficient in improving the mechanical properties. A novel strategy to achieve similar results is to utilize organosolv lignin, a renewable biopolymer with rigid aromatic backbone that has multiple active sites amenable for grafting heterogenous polymer units. In this study, a lignin-based triblock copolymer, namely lignin-grafted poly(diacetone acrylamide-co-2-hydroxypropyl acrylate) or LPDH, was successfully synthesized via ARGET-ATRP (activator regenerated by electron transfer-atom transfer radical polymerization) mechanism. The LPDH copolymers were found to exhibit higher ultimate tensile stress (≤6.3 ± 1.4 MPa) and Young’s modulus (194.2 ± 46.1 MPa), as well as significant (86 %) recovery of tensile strength and extensibility. Moreover, the LPDH copolymers could absorb UV radiation. Since, a commercially available organosolv lignin was directly utilized to prepare the copolymer without any purification, it is suggested that LPDH has potential to be manufactured on an industrial scale for self-healing, anti-UV coating applications. It also is hoped that the proposed synthetic strategy will inspire the development of renewable biomass-based polymers with similar functions.

Thermoresponsive Cationic Block Copolymer Brushes for Temperature-Modulated Stem Cell Separation.

Recently, cell separation methods have become important for preparing cells for transplantation therapy. In this study, a thermoresponsive cationic block copolymer brush is developed as an effective cell separation tool. This brush is prepared on glass surfaces using two steps of activator regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP). The cationic segment is prepared in the first step of the ARGET-ATRP of N,N-dimethylaminopropylacrylamide (DMAPAAm). In the second step, the thermoresponsive segment is prepared, attached to the bottom cationic segment, through ARGET-ATRP with N-isopropylacrylamide (NIPAAm). The cell adhesion behavior of the prepared thermoresponsive cationic copolymer, PDMAPAAm-b-PNIPAAm, brush is observed using umbilical cord-derived mesenchymal stem cells (UCMSC), fibroblasts, and macrophages. At 37 °C, all three types of cells adhere to the thermoresponsive cationic copolymer brush. Then, by reducing the temperature to 20 °C, the adhered UCMSC are detached from the copolymer brush, whereas the fibroblasts and macrophages remain adhered to the copolymer brush. Using this copolymer brush, UCMSC can be purified from the cell mixture simply by changing the temperature. Therefore, the prepared thermoresponsive cationic copolymer brush is useful as a cell separation tool for the purification of mesenchymal stem cells.

Fabrication of novel electrochemical immunosensor by mussel-inspired chemistry and surface-initiated PET-ATRP for the simultaneous detection of CEA and AFP

A functional electrochemical immunosensor was successfully designed for simultaneous and high sensitivity detection of carcinoembryonic antigen (CEA) and α-fetoprotein (AFP). This electrochemical immunosensor was mainly designed by surface-initiated poly(glycidyl methacrylate) (PGMA) from multi-walled carbon nanotubes (MWCNTs) with the methodology of mussel-inspired chemistry (polydopamine, PDA) and metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP). Controlled PGMA was initiated from MWCNTs, in which Br-functional PDA-modified MWCNTs and eosin Y (EY) were used as initiator and photocatalyst, respectively. The epoxy group of PGMA is reacted with ethylenediamine (EDA) by a ring-opening reaction, the amino and hydroxyl groups in the polymer chain provide numerous effective binding sites for carboxyl groups of signal molecules and capture antibodies, realizing highly sensitive electrochemical detection. Under optimized conditions, the obtained hybrid nanoprobes (Aq/PGMA-g-MWCNTs and Fc/PGMA-g-MWCNTs) were used as efficient electrochemical immunosensor to simultaneously detect CEA and AFP. It is worth noting that the electrochemical immunosensor performed a wide detection range and a low detection limit of CEA (163 fg/mL ~ 163 ng/mL, 56.1 fg/mL) and AFP (100 fg/mL ~ 100 ng/mL, 32.8 fg/mL), respectively. This high sensitivity and selectivity detection platform has a potential application in the simultaneous detection of more tumor markers.

Surface-initiated photoinduced electron transfer ATRP and mussel-inspired chemistry: Surface engineering of graphene oxide for self-healing hydrogels

In this manuscript, self-healable nanocomposite hydrogels were successfully fabricated by combining surface-initiated photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) with mussel-inspired chemistry. Using these efficient and eco-friendly methods, poly(4-vinylpyridine) (P4VP) was initiated on the surface of graphene oxide (GO) via PET-ATRP with polydopamine (PDA) as the anchor and 10-phenylphenothiazine (PhPTZ) as organic photocatalyst, respectively. After in-situ polymerization of acrylic acid, self-healing nanocomposite hydrogels were successfully obtained, and they had excellent tensile strength (about 6.94 MPa), toughness (605%) performance as well as self-healing efficiency (94.9% after 8 h).