Surface-initiated Reversible Addition-fragmentation Chain Research Articles

A smart material: Multi-stimulus-responsive composite microspheres prepared via RAFT polymerization as recyclable pickering emulsifiers and their application in stabilizing real oil phases

The development of smart composites to sustainably separate and recover oil from oily water had attracted much attention. In this study, tri-block (P(LMA-b-NIPAM-b-AA)) polymer brushes were controllably “grown on” the Fe3O4 surface by three-step surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization to prepare Fe3O4-P(LMA-b-NIPAM-b-AA) (MNPLNA) magnetic nanospheres with interfacial activity. The MNPLNA nanospheres were characterized to demonstrate the triple response of pH, temperature and magnetism. Meanwhile, the comparison experiments showed that the MNPLNA nanospheres with tri-block structure had excellent interfacial activity. Then, the O/W type of Pickering emulsion was prepared by using MNPLNA nanospheres as the particle emulsifier. The size variation pattern of Pickering emulsion was comprehensively investigated by adjusting the concentration of nanospheres, oil-water ratio, electrolyte concentration and polarity of oil phase. Pickering emulsions were controllably separated by the action of an external magnetic field, and could be reversibly switched at least 10 cycles between emulsified and broken states under the trigger of pH and temperature. In addition, MNPLNA nanospheres exhibited excellent emulsification properties for stabilizing variety of real oil phases (e.g., canola oil, kerosene, diesel and crude oil). Based on this, MNPLNA nanospheres were applied as smart multifunctional materials in simulated kerosene-containing wastewater separation. MNPLNA nanospheres could be used to recover kerosene with high recovery rate after 10 separation cycles under the stepwise action of pH, temperature and magnetic field.

Surface-initiated reversible addition fragmentation chain transfer of fluoromonomers: an efficient tool to improve interfacial adhesion in piezoelectric composites

Baryum titanate/P(VDF-co-TrFE) piezoelectric composites with sturdy interfaces thanks to surface-initiated RAFT polymerization prepared fluoropolymer brushes.

Sensitive electrochemiluminescence analysis of lung cancer marker miRNA-21 based on RAFT signal amplification.

An electrochemiluminescence approach based on surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) was developed for miRNA-21 detection for the first time. The SI-RAFT polymerization generates polymer chains with functional groups that are used to recruit luminol, enabling strong ECL signal output with low concentrations of miRNA-21, and greatly improving the detection sensitivity.

Ultrasensitive detection of CYFRA 21-1 DNA via SI-RAFT based in-situ metallization signal amplification

Cytokeratin fragment antigen 21-1 (CYFRA 21-1) DNA is a significant biomarker with relation to non-small cell lung cancer. Here, we described an ultrasensitive electrochemical biosensor for detection of CYFRA 21-1 DNA (target DNA, tDNA) via surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization-based DNA metallization signal amplification strategy. Specifically, 5′terminal modified thiol peptide nucleic acid (PNA) probes are immobilized on the gold electrode surface (by Au-S selfassembly) for the identification of specific tDNA sequences. After hybridization, the 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid (CPAD) is tethered to the PNA/DNA duplexes by means of the recognized phosphate-Zr4+-carboxylate chemistry. Subsequently, in the situation of C3H4O as the monomer, SI-RAFT polymerization can bring numerous aldehyde groups sites for the subsequent silver mirror reaction. The acrolein-polymers act as reductant to reduce Ag+ into Ag0, and then the silver particles are deposited on the polymer skeleton, which significantly amplifies the electrochemical signal. Under optimal conditions, the designed sensor for tDNA detection show a wide linear range from 100 aM to 1 nM, and the detection limit is as low as 0.89 aM. Moreover, the proposed biosensor exhibits prominent applicability for analysis of tDNA in serum samples and high selectivity for different mismatched oligonucleotide fragments. Given the proposed biosensor without extra natural enzyme or bio-labels, this method has enormous potential in bioanalysis.

A novel material poly(N-acryloyl-L-serine)-brush grafted kaolin for efficient elimination of malachite green dye from aqueous environments

In the present work, poly(N-acryloyl-L-serine) grafted-kaolin (PNALS@K) synthesized with the surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization method is reported for the efficient removal of malachite green (MG) dye from aqueous environments. The characterization of PNALS@K was carried out by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), energy dispersive x-ray spectroscopy (EDX), and contact angle measurements. The surface characterization analysis indicates there is a thin layer of PNALS on the kaolin surface. Four parameters (starting pH, starting MG concentration (Co), adsorbent dosage (m), and contact time (t)) were evaluated using response surface methodology (RSM) combined with central composite design (CCD) for the removal of MG by PNALS@K. The optimum adsorption conditions for the removal of MG using PNALS@K were determined as starting pH = 8.92, Co = 23.49 mg/L, m = 17.44 mg, and t = 72.2 min. The results indicated that PNALS@K has maximum adsorption decolorization performance of 98.90% for MG% removal at the optimal points. Moreover, adsorption data obeyed the Weber-Morris, liquid film diffusion and pseudo-second-order kinetic models. According to the isotherm results, it was also observed that Freundlich isotherm model presented a better fit.

Conversion from a natural mineral to a novel effective adsorbent: Utilization of pumice grafted with polymer brush for methylene blue decolorization from aqueous environments

The present work reports the adsorption yield of methylene blue (MB) from aqueous environments using pumice (PMC) coated with poly(N-[Tris (hydroxymethyl)methyl]acrylamide), PTHAM@PMC, by surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization. The synthesized PTHAM@PMC particles were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectrometry (ATR-FTIR), scanning electron microscopy (SEM) and water contact angle measurements. Results revealed that a homogeneous polymer layer was grafted on the PMC surface. Response surface methodology (RSM) with central composite design (CCD) was performed to optimize and to investigate the influence of independent parameters such as initial pH, initial MB concentration (Co, mg/L), adsorbent dosage (m, mg), contact time (t, min) and temperature (T, °C) for MB% removal with PTHAM@PMC. The results based on CCD indicated that the optimum initial pH, Co, m, t and T are 8.95, 52.53 mg/L, 40.5 mg, 67.28 min and 33.52 °C, respectively. The maximum removal efficiency of 98.68% and the maximum adsorption capacity of 68.998 mg/g were reached at these optimal points. Additionally, the kinetic, isotherm and thermodynamic studies were performed and the obtained results were evaluated. The great advantage of this work is that polymer brush grafted pumice had high adsorption capacity, fast adsorption kinetics, and high removal of MB. Considering all of these, it is thought that the constructed pumice with polymer brush will allow the improvement of novel procedures for the adsorption process.

Ultrasensitive Detection of DNA via SI-eRAFT and in Situ Metalization Dual-Signal Amplification.

In this work, we report a new amplification strategy based on electrochemically mediated reversible addition-fragmentation chain transfer (eRAFT) and in situ metalization for electrochemical detection of DNA. First, peptide nucleic acid (PNA) probes were immobilized on the surface of the gold electrode, and when they hybridized with the target DNA, the chain transfer agent (CTA), 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPAD), of RAFT was connected to the PNA/DNA heteroduplex formed by the coordination bonding of Zr4+. Then glycosyloxyethyl methacrylates (GEMA) were assembled on the surface of the electrode by electrochemically mediated surface-initiated reversible addition-fragmentation chain transfer (SI-eRAFT) to form a polymer-containing sugar glucose. Next, the o-hydroxyl groups on the polysaccharide molecular skeleton were oxidized to aldehyde groups by sodium periodate (NaIO4). The aldehyde groups generated then reduce silver ions to silver particles deposited on the electrode surface in situ, and this system was then subjected to differential pulse voltammetry (DPV). Under optimal conditions, the intensity of the stripping current and the logarithm of the target DNA (tDNA) concentration has a good linear relationship in the range of 10 aM to 1 pM (R2 = 0.996), and the detection limit can go down to 5.4 aM (S/N = 3). Moreover, the method is suitable for single-nucleotide polymorphism (SNP) analysis and has strong anti-interference ability for the analysis of target ssDNA in serum samples.

Magnetic nanoparticles coated with aminated polymer brush as a novel material for effective removal of Pb(II) ions from aqueous environments.

In the present study, a poly (vinylbenzyl chloride) grafted Fe3O4 nanoparticle (Fe3O4@PVBC) was prepared by surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization and subsequently coated with tris (aminoethyl) amine (TAEA). Then, Fe3O4@PVBC-TAEA nanoparticles were utilized as a novel adsorbent for removal of Pb(II) from aqueous media and optimal adsorption conditions were determined with response surface methodology (RSM). The used adsorbent was characterized by using X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). RSM with central composite design (CCD) was carried out to evaluate the effect of initial pH, initial Pb(II) concentration (C0, mg/L), adsorbent dosage (mg), and contact time (min). The optimum initial pH, C0, adsorbent dosage, and contact time were found to be 5.88, 46.51mg/L, 17.41mg, and 108.21min, respectively. The maximum removal efficiency and adsorption capacity were 97.07% and 129.65mg/g under these conditions, respectively. The kinetic data revealed that the adsorption mechanism could be best explained by the pseudo-second-order and Weber-Morris models. The isotherm studies found that both the Langmuir and Freundlich isotherm models fitted the experimental data well. The thermodynamic analysis indicated that the adsorption nature is exothermic, applicable, and spontaneous.

Chemical Synthesis and Characterization of Poly(poly(ethylene glycol) methacrylate)-Grafted CdTe Nanocrystals via RAFT Polymerization for Covalent Immobilization of Adenosine.

This paper describes the functionalization of poly(poly(ethylene glycol) methacrylate) (PPEGMA)-grafted CdTe (PPEGMA-g-CdTe) quantum dots (QDs) via surface-initiated reversible addition–fragmentation chain transfer (SI-RAFT) polymerization for immobilization of adenosine. Initially, the hydroxyl-coated CdTe QDs, synthesized using 2-mercaptoethanol (ME) as a capping agent, were coupled with a RAFT agent, S-benzyl S′-trimethoxysilylpropyltrithiocarbonate (BTPT), through a condensation reaction. Then, 2,2′-azobisisobutyronitrile (AIBN) was used to successfully initiate in situ RAFT polymerization to generate PPEGMA-g-CdTe nanocomposites. Adenosine-above-PPEGMA-grafted CdTe (Ado-i-PPEGMA-g-CdTe) hybrids were formed by the polymer shell, which had successfully undergone bioconjugation and postfunctionalization by adenosine (as a nucleoside). Fourier transform infrared (FT-IR) spectrophotometry, energy-dispersive X-ray (EDX) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy results indicated that a robust covalent bond was created between the organic PPEGMA part, cadmium telluride (CdTe) QDs, and the adenosine conjugate. The optical properties of the PPEGMA-g-CdTe and Ado-i-PPEGMA-g-CdTe hybrids were investigated by photoluminescence (PL) spectroscopy, and the results suggest that they have a great potential for application as optimal materials in biomedicine.

Preparation and application of temperature-sensitive affinity chromatographic materials for enrichment of phosphoric acid compounds

Based on the surface initiated-reversible addition fragmentation chain transfer (SI-RAFT) method, an immobilized metal ion affinity chromatographic material, silica@ploy(N-isopropylacrylamide-co-(aminomethyl)phosphonic acid)-titanium(Ⅳ) (silica@p(NIPAAm-co-AMPA)-Ti4+), was synthesized by the method of rapid introduction of functional groups. The synthesis of the material was confirmed by FT-IR and X-ray photoelectron spectroscopy. The grafting ratio and lower critical solution temperature (LCST) of the material were measured by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the material had excellent temperature-sensitive properties and could successfully capture and release adenosine triphosphate successfully. The service life of the material could be extended by online supplementation of Ti4+.

Preparation of Polyamidoxime/Magnetic Graphene Oxide Composite and Its Application for Efficient Extraction of Uranium(VI) from Aqueous Solutions in an Ultrasonic Field

In this work, the polyamidoxime functionalized magnetic graphene oxide (mGO-PAO) was prepared via the surface-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization, characterized by TEM, FT-IR, VSM, and TGA techniques, and applied for the extraction of uranium(VI) from aqueous solutions in an ultrasonic field. The effects of pH, contact time, initial uranium(VI) concentration, temperature, and competitive ions on the adsorption of U(VI) were investigated. The adsorption speed of mGO-PAO for U(VI) was found to be 18 times faster in the ultrasonic field than in the shaking mode, and the adsorption equilibrium, to be reached within 2 min. When the U(VI) concentration was 10 mg/L, the temperature, 298 K, and pH, 6.0, the removal rate of U(VI) reached 98.24% with high selectivity. The adsorption kinetics and isotherm data were well described by the pseudo-second-order and Langmuir models, respectively. The thermodynamic parameters suggested that the adsorption of U(VI) was a typical ...

Light-triggered pH/thermal multisensitive polyelectrolyte/ITO glass hybrid electrode

Surfaces with stimuli-responsive properties have shown prominent applications in bioengineering, controlled drug release and biosensors in recent years. In this work, we report a surface-initiated reversible addition–fragmentation chain transfer polymerization method to graft azobenzene-containing diblock copolymer (azo-BCP) brushes onto an Indium Tin Oxide (ITO) glass surface. In this method, a sequential azo block serves as the outer layer that controls the closure or opening of the brushes, and the second block (PDMAEMA) acts as the inner layer that switches between swollen and collapsed chain states in response to different pH values and temperatures. Upon exposure to UV light, the ITO surface became more hydrophilic (>10° change of contact angles), and its friction coefficient (0.5–0.9) increased; this suggests a loose aggregation of the azo block. Additionally, the ion conductivity of the ITO surface can be influenced by the aggregation state of the azo-BCP brushes, thus leading to the transportation of light-triggered ions under various pH values and temperatures. This work provides a deep understanding of the surface properties of a sensitive hybrid material upon various stimuli for electrode purpose, thereby paving the way for the development of bioengineering and environmental sensory applications.

Efficient and selective separation of metronidazole from human serum by using molecularly imprinted magnetic nanoparticles.

Magnetic molecularly imprinted nanoparticles were prepared through surface-initiated reversible addition fragmentation chain transfer polymerization by using metronidazole as a template. The molecularly imprinted magnetic nanoparticles were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The adsorption characteristics were also investigated and the kinetics of the adsorption of metronidazole on the imprinted nanoparticles were described by the second-order kinetic model with the short equilibrium adsorption time (30min). The adsorption isotherm was well matched with the Langmuir isotherm in which the maximum adsorption capacity was calculated to be 40.1mg/g. Furthermore, the imprinted magnetic nanoparticles showed good selectivity as well as reusability even after six adsorption-desorption cycles. The imprinted magnetic nanoparticles were used as a sorbent for the selective separation of metronidazole from human serum. The recoveries of metronidazole from human serum changed between 97.5 and 99.8% and showed similar sensitivity as an enzyme-linked immunoassay method. Therefore, the molecularly imprinted magnetic nanoparticles might have potential application for the selective and reliable separation of metronidazole from biological fluids in clinical applications.

High Performance Capacitors Using BaTiO3 Nanowires Engineered by Rigid Liquid-crystalline Polymers

Capacitors that provide high power density have attracted scientific and commercial interest, while often suffering from low energy density. Preparing a core–shell structured ceramic is regarded as a kind of effective method to improve the energy density, which is largely determined by the shell in the interfacial region. However, the current state-of-the-art of interfacial layer modification is predominantly based on utilizing flexible polymers, which are random polymer coils that collapse on the surface of any modified ceramic nanoparticles. Because of the characteristic properties of rigidity and orientation, the liquid-crystalline polymer poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) is utilized to engineer the interfacial layer thickness on BaTiO3 nanowire surfaces via surface-initiated reversible addition–fragmentation chain transfer polymerization (RAFT) method, in this paper. As a result, a high discharged energy density of 7.5 J/cm3 and an energy efficiency of 55.1% at 300 MV/m are a...

Matrix-Free Polymer Nanocomposite Thermoplastic Elastomers

Thermoplastic elastomer (TPE) grafted nanoparticles were prepared by grafting block copolymer poly(styrene-block-(n-butyl acrylate)) onto silica nanoparticles (NPs) via surface-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization. The effects of polymer chain length and graft density on the mechanical properties were investigated using films made solely from the grafted NPs. The ultimate tensile stress and elastic modulus increased with increasing PS chain length. The dispersion of the silica NPs and the microphase separation of the block copolymer in the matrix-free polymer nanocomposite were investigated using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The higher polymer graft density TPEs exhibited better microphase separation of the block copolymers and more uniform silica NP dispersion than lower polymer graft density TPEs with similar polymer chain length and composition.

Surface-imprinted magnetic nanoparticles for the selective enrichment and fast separation of fluoroquinolones in human serum.

Surface enrofloxacin-imprinted magnetic nanoparticles were prepared for the selective recognition and fast separation of fluoroquinolones in human serum by surface-initiated reversible addition fragmentation chain transfer polymerization. The surface morphology and imprinted behavior were investigated and optimized. The living/controlled nature of reversible addition-fragmentation chain transfer polymerization reaction allowed the successful construction of well-defined imprinted polymer layer outside the Fe3 O4 core. Such molecularly imprinted polymers exhibited superparamagnetic properties and specific recognition toward fluoroquinolones. Combined with reversed-phase high-performance liquid chromatography, the prepared molecularly imprinted polymers were used for the selective enrichment and analysis of fluoroquinolones in human serum samples. The recoveries of four fluoroquinolones were 86.8-95.3% with relative standard deviations of 2.0-6.8% (n=3). Such magnetic molecularly imprinted polymers have great prospects in the separation and enrichment of trace analysts in complex biological samples.

Synthesis and characterization of photoluminescent Eu(III) coordinated with poly(2-hydroxyethyl methacrylate) grafted SiO2 nanoparticles via surface RAFT polymerization

ABSTRACTA novel fluorescent nanohybrid complex comprising of SiO2 nanoparticles, poly(2-hydroxyethyl methacrylate) (PHEMA), and photoluminescent (Eu3+) was synthesized by a combination of controlled surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization and coordination chemistry. Initially, PHEMA was grafted from the surface of SiO2 NPs by SI-RAFT and then reacted with succinic anhydride to provide carboxyl acid groups on the external layers of SiO2-PHEMA nanohybrids. The subsequent coordination of the nanohybrids with Eu3+ ions successfully afforded the photoluminescent Eu3+ tagged SiO2-PHEMA nanohybrid complex (SiO2-PHEMA-Eu3+). The structure and fluorescence properties of the Eu3+ coordinated nanohybrid complex were investigated using the respective physical and spectral studies.

Fabrication and adsorption properties of novel magnetic graphene oxide composites for removal of methylene blue

ABSTRACTThe hybrid material of magnetic graphene oxide (MNPs/GO) was prepared with a facile route and adsorption properties for removal of methylene blue (MB) were investigated. Initially, the surface of magnetic nanoparticles (MNPs) was modified with poly(glycidyl methacrylate) by the surface-initiated reversible addition fragmentation chain transfer (RAFT) polymerization. The modified MNPs and graphene oxide (GO) were fabricated to form MNPs/GO in N,N-dimethylformamide at 60°C. The composites were characterized by using XRD, SEM, TEM, and vibrating sample magnetometry analyses. The adsorptive removal of MB on the adsorbent obeyed a pseudo-second-order kinetic whose equilibrium data were fitted well to the Langmuir isotherm model and the maximum MB uptake of MNPs/GO was estimated from this model to be 153.85 mg/g. MNPs/GO adsorbent could be recycled and maintained 75.3% of its initial adsorption capacity for MB after five regeneration cycles.

Photo-induced in situ crosslinking of polymer brushes with dimethyl maleimide moieties for dynamically stimulating stem cell differentiation

We designed photo-crosslinkable polymer brushes with dimethylmaleimide moieties, in order to demonstrate dynamic stimulation of cell differentiation in mesenchymal stem cells (MSCs). The polymer brushes were synthesized by surface-initiated reversible addition fragmentation chain transfer polymerization using dimethylmaleimide ethyl methacrylate and methyl methacrylate on a chain transfer agent-immobilized glass surface. The polymer brushes were crosslinked by photodimerization of the dimethylmaleimide moieties within polymer chains with stem cells present on the surface. In order to evaluate the effects of in situ photo-induced crosslinking of the polymer brushes on gene expression of stem cells, human bone marrow MSCs were cultured under static and dynamic culture conditions for 7 days. Expression of the osteocalcin (Ocn) gene in MSCs was used as an indicator of osteoblast differentiation under dynamic culture conditions. Structural conversion from non-crosslinked polymer brushes to crosslinked polymer brushes increased the expression of Ocn by 1.4-fold in the presence of adhered cells, compared with non-crosslinked polymer brushes under static culture conditions. These results suggest that MSCs recognized surface conversion from non-crosslinked to crosslinked structures, which resulted in altered differentiation lineages. Therefore, photo-crosslinkable surfaces with dimethyl maleimide moieties are potential novel materials for dynamically stimulating MSC differentiation.

A new approach for synthesis of SiO2/poly(2-hydroxyethyl methacrylate):Tb3+ nanohybrids by combination of surface-initiated raft polymerization and coordination chemistry

A facile strategy for growing the poly(2-hydroxyethyl methacrylate) encapsulated on the surface of SiO2 nanoparticles (SiO2/PHEMA) as a molecular host matrix for the luminescent Tb3+ via a combination of surface-initiated reversible addition fragmentation chain transfer polymerization and coordination chemistry was successfully developed. The structure, morphology and fluorescence properties of the materials were investigated using relevant physical and spectral techniques. The core–shell structure and uniform dispersion of SiO2/PHEMA and SiO2/PHEMA:Tb3+ complexes were found according to SEM and TEM analyses while their surface bonding characteristics were determined via FT-IR analysis. In photoluminescence measurement, the SiO2/PHEMA:Tb3+ nanoparticles showed characteristic emissions of Tb3+ with the strongest (5D4 → 7F5) green emission without detectable emissions of ligands, demonstrating that SiO2 framework covalently bonded with PHEMA segments acting as an efficient matrix for sensitization of fluorescent Tb3+ ions.