Surface-initiated Atom-transfer Polymerization Research Articles

On-line temperature-responsive restricted access material of sample preparation technique coupling with liquid chromatography for detection of tetracycline residues in milk

Effort of sample preparation has been working towards the automation and improvement of accuracy. Development of on-line sample preparation coupled with liquid chromatography (LC) is a promising way. In this study, an on-line extraction-LC automated analysis was proposed based on a temperature-sensitive restricted access material (RAM) for the determination of tetracycline residues (TCs) in milk. The RAM was synthesized using silica as substrate by the two-step surface initiated-atom transfer polymerization (SI-ATRP), styrene (St), sodium 4-vinylbenzenesulfonate (Nass) and a lower critical solution temperature (LCST)-responsive n-vinylcaprolactam (VCl) were conjugated to fabricate multiple interaction-adsorption sites of P(St-co-Nass-co-VCl) on silica interior, while an upper critical solution temperature (UCST)-responsive sulfobetaine methacrylate (SBMA) was then block polymerized to form zwitterionic exclusion sites on exterior. Thereafter, the RAM was packed as extraction column to be fixed into LC ahead of C18 analytical column, establishing automatic analysis by rotation of switching valve. In conjunction with LCST and UCST dual-responsive properties to adjust the hydrophobic-hydrophilic transition of the grafted P(St-co-Nass-co-VCl)-b-PSBMA chains, the RAM column acquires the best extraction of TCs and meanwhile the furthest removal of proteins at about 30 ℃ of column temperature. And using the proposed automatic analysis for monitoring of TCs in milk, a wide linearity (20–900 ng mL−1), low limit of detection (1.0 ng mL−1) and limit of quantification (2.5 ng mL−1) as well as good inter-day (<3.9 % RSD) and intra-day precision (<4.8 % RSD) with satisfactory recoveries (97.2–101.9 %) show the superior efficiency. It is believed that the introduction of temperature-sensitive RAM to construct on-line extraction is a powerful tool for detecting trace substances in scientific analyses.

Polymer-Grafted Nanoparticles with Variable Grafting Densities for High Energy Density Polymeric Nanocomposite Dielectric Capacitors.

Designing high energy density dielectric capacitors for advanced energy storage systems needs nanocomposite-based dielectric materials, which can utilize the properties of both inorganic and polymeric materials. Polymer-grafted nanoparticle (PGNP)-based nanocomposites alleviate the problems of poor nanocomposite properties by providing synergistic control over nanoparticle and polymer properties. Here, we synthesize "core-shell" barium titanate-poly(methyl methacrylate) (BaTiO3-PMMA) grafted PGNPs using surface-initiated atom transfer polymerization (SI-ATRP) with variable grafting densities of (0.303 to 0.929) chains/nm2 and high molecular masses (97700 g/mL to 130000 g/mol) and observe that low grafted density and high molecular mass based PGNP show high permittivity, high dielectric strength, and hence higher energy densities (≈ 5.2 J/cm3) as compared to the higher grafted density PGNPs, presumably due to their "star-polymer"-like conformations with higher chain-end densities that are known to enhance breakdown. Nonetheless, these energy densities are an order of magnitude higher than their nanocomposite blend counterparts. We expect that these PGNPs can be readily used as commercial dielectric capacitors, and these findings can serve as guiding principles for developing tunable high energy density energy storage devices using PGNP systems.

The hydrophilic boronic acid-poly(ethylene glycol) methyl ether methacrylate copolymer brushes functionalized magnetic carbon nanotubes for the selective enrichment of glycoproteins

An efficient and selective glycoproteins enrichment platform is essential to glycoprotein biomarkers in early clinic diagnostics. In this work, the poly (ethylene glycol) methyl ether methacrylate (PEGMA) and 4-vinylphenylboronic acid (VPBA) copolymer brushes grafted magnetic carbon nanotubes composite MCNTs@p (PEGMA-co-VPBA) was prepared by surface-initiated atom transfer polymerization and applied for the selective enrichment of glycoproteins from the complex biological samples. The as-prepared MCNTs@p (PEGMA-co-VPBA) nanocomposite was characterized by Fourier transform-infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). The MCNTs@p (PEGMA-co-VPBA) can recognize and bind specifically for glycoproteins via strong boronate affinity and excellent hydrophilicity and shows a really low non-specificity adsorption capability for non-glycoproteins. The adsorption capacity of MCNTs@p (PEGMA-co-VPBA) towards glycoproteins transferrin (Trf), horseradish peroxidase (HRP), and non-glycoproteins cytochrome c (Cyt C), lysozyme (Lyz) is 253.3 mg g−1, 51.1 mg g−1, 13.9 mg g−1 and 14.5 mg g−1, respectively. Furthermore, MCNTs@p (PEGMA-co-VPBA) can be applied to extract glycoproteins directly from egg white samples. These results demonstrated that MCNTs@p (PEGMA-co-VPBA) could be a potential affinity adsorbent in glycoprotein enrichment.

Salt- and thermo-responsive polyzwitterionic brush prepared via surface-initiated photoiniferter-mediated polymerization

Zwitterionic polymer brushes with strong anti-polyeletrolyte effect have shown great potential in applications of tunable friction, protein absorption/desorption, and “killing and release” antibacterial surfaces. However, such polymer brushes are presently prepared by surface-initiated atom transfer polymerization (SI-ATRP) which is a sophisticated and time-consuming process. In this paper, a simple method, i.e. surface-initiated photoiniferter-mediated polymerization (SI-PIMP) was used to prepare poly (3-(dimethyl (4-vinylbenzyl) ammonio) propyl sulfonate) (polyDVBAPS) brush on silicon wafer. It was shown that the reaction solution had a significant effect on the growth rate and surface roughness of the resulting brushes. In suitable solution (e.g. 0.53 M NaCl solution) brushes with controllable thickness and smooth surface could be obtained. Contact angle and surface friction measurement indicated that the brush prepared by SI-PIMP showed identical salt-responsive properties compared to the brushes from SI-ATRP. In addition, the thermo-responsive properties of polyDVBAPS brush was also investigated, which was further used for tuning surface friction of the brush. Due to the thermo-responsive properties, polyDVBAPS brush showed super lubrication (u ∼ 10−3) in water and NaCl solutions with low concentrations (0.1 M and 0.53 M) when the temperature was increased to 70 °C, 65 °C and 55 °C respectively. Although ultralow friction could be achieved under the conditions of different temperature and salt concentration, the stability against long-term friction highly depended on the environmental condition. At 40 °C and in 1.0 M NaCl solution, ultralow friction was well retained up to 1500 s, while under other conditions (saturated NaCl solution of 25 °C and 0.53 M NaCl solution of 55 °C), aqueous lubrication was rapidly deteriorated. This work not only demonstrated the practicability of the SI-PIMP for the preparation of polyDVBAPS brush, but also realized the tunable surface friction of such polyzwitterionic brush under different environmental conditions, extending its applications in both academic and industrial communities.

Modulation of Surface-Initiated ATRP by Confinement: Mechanism and Applications.

The mechanism of surface-initiated atom transfer polymerization (SI-ATRP) of methacrylates in confined volumes is systematically investigated by finely tuning the distance between a grafting surface and an inert plane by means of nanosized patterns and micrometer thick foils. The polymers were synthesized from monolayers of photocleavable initiators, which allow the analysis of detached brushes by size-exclusion chromatography (SEC). Compared to brushes synthesized under “open” polymerization mixtures, nearly a 4-fold increase in brush molar mass was recorded when SI-ATRP was performed within highly confined reaction volumes. Correlating the SI-ATRP of methyl methacrylate (MMA), with and without “sacrificial” initiator, to that of lauryl methacrylate (LMA) and analyzing the brush growth rates within differently confined volumes, we demonstrate faster grafting kinetics with increasing confinement due to the progressive hindering of CuII-based deactivators from the brush propagating front. This effect is especially noticeable when viscous polymerization mixtures are generated and enables the synthesis of several hundred nanometer thick brushes within relatively short polymerization times. The faster rates of confined SI-ATRP can be additionally used to fabricate, in one pot, precisely structured brush gradients, when volume confinement is continuously varied across a single substrate by spatially tuning the vertical distance between the grafting and the confining surfaces.

Protein Reduction and Dialysis-Free Work-Up through Phosphines Immobilized on a Magnetic Support: TCEP-Functionalized Carbon-Coated Cobalt Nanoparticles.

Tris(2-carboxyethyl)phosphine (TCEP) is an often-used reducing agent in biochemistry owing to its selectivity towards disulfide bonds. As TCEP causes undesired consecutive side reactions in various analytical methods (e.g., gel electrophoresis, protein labeling), it is usually removed by means of dialysis or gel filtration. Here, an alternative method of separation is presented, namely the immobilization of TCEP on magnetic nanoparticles. This magnetic reagent provides a simple and rapid approach to remove the reducing agent after successful reduction. A reduction capacity of 70 μmol per gram of particles was achieved by using surface-initiated atom transfer polymerization.

Poly(N-isopropyl acrylamide)-coated surfaces: Investigation of the mechanism of cell detachment.

Although there is a great deal of research focused on cell sheet engineering from polymers such as poly(N-isopropyl acrylamide) (pNIPAM), the biocompatibility of pNIPAM surfaces and the nature of cellular detachment from this polymer is still unclear. The most extensive study of the mechanism of detachment proposed a two-step process, with a first (passive) phase involving hydration of pNIPAM chains, and the second (active) phase involving cellular metabolism. However, a number of studies performed successful cell sheet detachment from pNIPAM-grafted surfaces at low temperatures which calls this hypothesis into question. Furthermore, although it has been demonstrated that low-temperature cell sheet detachment using pNIPAM-grafted surfaces is less destructive than other methods of detachment, it has not been investigated if cell sheet detachment removes a portion of pNIPAM from the surfaces as well. It is essential to know if any fragments of the polymer are removed along with the cells, as small polymer fragments could have cytotoxic effects on the cells. This is especially important if these cells are used for the generation of tissues used for transplantation. In this work, the mechanism of cell detachment from pNIPAM coated surfaces is investigated by testing how temperature and presence of an adenosine triphosephase inhibitor affect cellular detachment. Surface initiated atom transfer polymerization (ATRP) was utilized to synthesize thermoresponsive atrpNIPAM surfaces. pNIPAM surfaces were labeled to assess whether cell sheet detachment from pNIPAM is accompanied by the removal of pNIPAM from the substrate itself. Using a semipermeable superstrate, cell sheets were transferred to a secondary culture dish to assess whether cell detachment resulted in any pNIPAM removal. In addition, the function of the transplanted bovine aortic endothelial cells was assessed by determining whether they would proliferate and grow on a new secondary substrate.

Surface charge control for zwitterionic polymer brushes: Tailoring surface properties to antifouling applications

HypothesisElectrostatic interactions play an important role in adhesion phenomena particularly for biomacromolecules and microorganisms. Zero charge valence of zwitterions has been claimed as the key to their antifouling properties. However, due to the differences in the relative strength of their acid and base components, zwitterionic materials may not be charge neutral in aqueous environments. Thus, their charge on surfaces should be further adjusted for a specific pH environment, e.g. physiological pH typical in biomedical applications. ExperimentsSurface zeta potential for thin polymeric films composed of polysulfobetaine methacrylate (pSBMA) brushes is controlled through copolymerizing zwitterionic SBMA and cationic methacryloyloxyethyltrimethyl ammonium chloride (METAC) via surface-initiated atom transfer polymerization. Surface properties including zeta potential, roughness, free energy and thickness are measured and the antifouling performance of these surfaces is assessed. FindingsThe zeta potential of pSBMA brushes is −40mV across a broad pH range. By adding 2% METAC, the zeta potential of pSBMA can be tuned to zero at physiological pH while minimally affecting other physicochemical properties including dry brush thickness, surface free energy and surface roughness. Surfaces with zero and negative zeta potential best resist fouling by bovine serum albumin, Escherichia coli and Staphylococcus aureus. Surfaces with zero zeta potential also reduce fouling by lysozyme more effectively than surfaces with negative and positive zeta potential.

Initial Cell Adhesion on Well-Defined Surface by Polymer Brush Layers with Varying Chemical Structures

To understand cellular responses at the interface between biological system and artificial materials, we considered several surface properties of the materials. Controlled surface properties were achieved for preparation of well-defined polymer brush substrates with varying chemical structures, which were prepared by surface-initiated atom transfer polymerization. The substrates were covered with hydrophilic polymer brush layers with anionic groups, cationic groups, and zwitterionic groups as well as nonionic hydroxyl groups. In addition, surface covered with hydrophobic fluoroalkyl groups was prepared. Initial cell adhesion was examined using human cervical adenocarcinoma epithelial cell line, as a model cell, and the cell adhesion onto the polymer brush substrates was evaluated related with cell adhesive protein adsorption. The number and morphology of adherent cells were clearly dependent on the surface ζ-potentials of polymer brush substrates. In contrast, no significant correlation was observed with respect to the hydrophilic/hydrophobic nature of the substrate, which was evaluated by static air contact angles at the surface in water. The number of adherent cells on the substrate increased with the absolute value of the surface ζ-potentials, and the cells did not adhere onto the substrate with zero surface ζ-potential, that is the polymer brush substrate with zwitterionic groups. The amount of protein adsorbed onto the substrates influenced cell adhesion, as did the surface ζ-potentials of the substrates. Therefore, we concluded that the initial cell adhesion is correlated with the surface ζ-potential on the substrate with polymer brush structures. The surface ζ-potential will be a good parameter for designing a cell adhesion-resistance substrate to prepare temporary or single-use biomedical devices.

Polyol-grafted polysulfone membranes for boron removal: Effects of the ligand structure

In this study, a series of polysulfone membranes grafted with polyol polymers have been synthesized and used for boron removal via complexation of the vicinal diol structure with boric acid. The membranes were prepared by non-solvent induced phase inversion of the chloromethylated polysulfone followed by surface-initiated atom transfer polymerization (ATRP). Three multi-hydric methacrylate monomers including 2,3-dihydroxypropyl methacrylate (HPMA), 3-(N-glucidol-N-methyl)amino-2-hydroxypropyl methacrylate (GMHP), and 2-(bis(2,3-dihydroxypropyl)amino)ethyl methacrylate (HAEM) were used. The membrane was characterized by ATR-FTIR, XPS, SEM, water contact angle (WCA) and water flux measurement. The effects of the ligand structure on the adsorption thermodynamics and kinetics were studied in detail. A series of polyol-grafted membranes with boron uptake ranging from 0.20 to 0.46mmol/g were obtained. The boron complexing efficiency of HAEM, GMHP and HPMA is calculated to be 222%, 175% and 62%, respectively. We believe the presence of the amino group, high vicinal diol content and the branched structure are all beneficial to the complexing efficiency. The adsorption isotherms conform to the Langmuir model and the adsorption kinetics obey the pseudo-second-order rate expression. Optimization of the ligand structure is helpful to increase the boron uptake but has limited benefits on the boron adsorption rate.

Novel heparin-mimicking polymer brush grafted carbon nanotube/PES composite membranes for safe and efficient blood purification

Nowadays, polymeric membrane based hemodialysis is considered to be the most practical approach for the treatment of kidney failure. To develop advanced hemodialysis membrane integrated with favorable blood and cell compatibilities and efficient blood purification ability, novel biocompatible composite membranes consisting of heparin-mimicking polymer brush functionalized carbon nanotubes (f-CNTs) and polyethersulfone (PES) are designed. Firstly, surface initiated atom transfer polymerization (SI-ATRP) is applied to synthesize heparin-mimicking polymer brush (contained the sodium styrene sulfonate (SS) and methyl ether methacrylate (EGMA) units) grafted CNT. Then, the f-CNT/PES composite membranes are prepared by a liquid–liquid phase separation technique. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results indicated that the f-CNT would not cause severe damage on the membrane morphologies. Systemic protein ultrafiltration experiment indicated that the heparin-mimicking composite membranes owned satisfied antifouling property and protein rejection ratio. Further blood compatibility evaluation revealed that the composite membranes had decreased protein adsorption, prolonged clotting time, and suppressed platelet adhesion compared to pristine PES membrane. The results of human embryonic hepatocytes (LO-2) culture revealed that the cyto-compatibility of the modified membrane was enhanced by the blending of heparin mimicking polymer functionalized CNT. Furthermore, with the addition of f-CNT, the composite membranes showed remarkably increased removal efficiency of uremic toxin. In general, the fabricated heparin-mimicking f-CNT/PES composite membranes exhibited anti-fouling ability in ultrafiltration, excellent blood and cell compatibility and efficient toxic molecules removal ratio, thus present great potential for various applications, such as hemodialysis and bio-artificial liver support. Furthermore, the proposed method might forward the fabrication of advanced hemodialysis membrane by integrating functional nanomaterials and bioactive polymers.

Amplification of Surface-Initiated Ring-Opening Metathesis Polymerization of 5-(Perfluoro-n-alkyl)norbornenes by Macroinitiation

This article reports the enhanced rate of the surface-initiated polymerization (SIP) of 5-(perfluoro-n-alkyl)norbornenes (NBFn) by combining two SIP techniques, namely surface-initiated atom-transfer polymerization (SI-ATRP) to grow a macroinitiator and surface-initiated ring-opening metathesis polymerization (SI-ROMP) to produce the final coating. This polymerization approach promotes the rapid growth of dense partially fluorinated coatings that are highly hydrophobic and oleophobic and yield thicknesses from 4-12 μm. Specifically, the growth rate and the limiting thickness of pNBFn with different side chain lengths (n = 4, 6, 8, and 10) at various monomer concentrations and temperatures are evaluated through two approaches: growing the polymer from an initiator-terminated monolayer (control) or from a modified poly(2-hydroxyethyl methacrylate) (PHEMA) macroinitiator. X-ray photoelectron spectroscopy (XPS) analysis shows that 38% of the hydroxyl termini in the macroinitiator react with a norbornenyl diacid chloride (NBDAC) molecule, and 7% of such anchored norbornenyl groups react with a catalyst molecule. The kinetic data have been modeled to determine the propagation velocity and the termination rate constant. The PHEMA macroinitiator provides thicker films and faster growth as compared to the monolayer, achieving a 12 μm thick coating of pNBF8 in 15 min. Increasing the monomer side chain length, n, from 4 to 10 improves the growth rate and the limiting polymer thickness. Performing the polymerization process at higher temperature increases the growth rate and the limiting thickness as evidenced by an increase in the film growth rate constant. Arrhenius plots show that the reactions involved in the macroinitiation process exhibit lower activation energies than those formed from a monolayer. Electrochemical impedance spectroscopy reveals that the films exhibit resistance against ion transport in excess of 1 × 10(10) Ω·cm(2).

Fabrication of an SPR Sensor Surface with Antifouling Properties for Highly Sensitive Detection of 2,4,6-Trinitrotoluene Using Surface-Initiated Atom Transfer Polymerization

In this study, we modified a surface plasmon resonance immunosensor chip with a polymer using surface-initiated atom transfer polymerization (SI-ATRP) for the highly sensitive detection of 2,4,6-trinitrotoluene (TNT). To immobilize a TNT analogue on the polymer, mono-2-(methacryloyloxy)ethylsuccinate (MES), which has a carboxyl group, was used in this study. However, the anti-TNT antibody may adsorb non-specifically on the polymer surface by an electrostatic interaction because MES is negatively charged. Therefore, a mixed monomer with MES and diethylaminoethylmethacrylate (DEAEM), which has a tertiary amino group and is positively charged, was prepared to obtain electroneutrality for suppressing the nonspecific adsorption. The detection of TNT was performed by inhibition assay using the polymer surface. To ensure high sensitivity to TNT, the affinity between the surface and the antibody was optimized by controlling the density of the initiator for ATRP by mixing two types of self-assembled monolayer reagents. As a result, a limit of detection of 5.7 pg/mL (ppt) for TNT was achieved using the optimized surface.

Construction of myoglobin imprinted polymer films by grafting from silicon surface

Molecularly imprinted polymer (MIP) films on silicon wafers were prepared by surface-initiated atom transfer polymerization (ATRP). 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate were used as the functional monomer and the cross-linking agent, respectively. Myoglobin (Mb) was selected as the template molecule to form the MIP films. Various characterization techniques including ellipsometry, contact-angle goniometer, atomic force microscopy, grazing angle-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, were used to characterize the films. Ellipsometry was also used to quantify and compare the binding capacity of the MIP and nonimprinted polymer (NIP) films. The MIP films exhibited higher rebinding capacity than the NIP films at all solution concentrations of Mb. A selectivity coefficient of 3.15 was achieved for the MIP films prepared against the Mb template molecule.

Thermoresponsive graphene nanosheets by functionalization with polymer brushes

We report the preparation of thermoresponsive graphene nanosheets functionalized by the polymer brushes. This approach involves the direct growth of thermoresponsive polymer brushes from functional graphene sheets (FGSs) by chemical modification with initiators followed by extension with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) through surface-initiated atom transfer radical polymerization. The highly controllable polymerization method affords the hybrid FGS-PDMAEMA with tailorable length of PDMAEMA brushes possessing the average molecular weight ( M n ) ranging from 7.4 × 10 3 to 6.0 × 10 4 with low molecular weight distributions ( M w / M n = 1.09–1.22). The resulting FGS-PDMAEMA was carefully characterized with a number of techniques, including elemental analysis, thermogravimetric analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy, all supporting the successful integration of polymer brushes onto the surface of FGS. Most importantly, we accomplished the reversible phase transfer of this hybrid FGS-PDMAEMA between aqueous and organic phases via temperature control by taking advantage of the thermoresponsive nature of PDMAEMA brushes. Moreover, the composite film prepared by depositing the suspensions of FGS-PDMAEMA demonstrated the facile control over the wettability upon temperature changes. This tailored control over dispersion in water, selective solubilization between aqueous and organic solvents, and wettability control upon temperature variation have a significant impact on the ability to improve properties of hybrid graphene-based materials. Because of the highly versatile and tunable properties of surface-initiated atom transfer polymerization, we anticipate that the general concept presented here offers a unique potential platform for integrating responsive polymers for graphene nanosheets for advanced electronic, energy, and sensor applications.

Size exclusion chromatography of quantum dots by utilizing nanoparticle repelling surface of concentrated polymer brush

We have found that the concentrated poly(methyl methacrylate) (PMMA) brush showed the very good nanoparticles (NPs) repellency in its good solvent, e.g. tetrahydrofuran (THF). Whereas the oil- and hydro-phobic (fluorinated), hydrophobic and hydrophilic surfaces adsorbed a lot of NPs. The repellency of NPs did not depend on the surface nature of the NPs. Preparing absorption free columns for size exclusion chromatography (SEC) may enable us to separate quantum dots (QDs) and NPs according to their size. By installing the concentrated PMMA brush into silica monolith columns, we tried to achieve SEC of QDs and NPs. The concentrated PMMA brush immobilized silica monolith columns were prepared by surface initiated atom transfer polymerization of MMA. As a result, we have succeeded in separating QDs according to their size. This SEC system may be advantageous because it can be used in good solvents of the brush regardless of the stability of the surface modifier layer on the NPs.