Grafting of gold nanoparticles and nanorods on plasma-treated polymers by thiols

Grafting of gold nanoparticles and nanorods on the surface of polymers, modified by plasma discharge, is studied with the aim to create structures with potential applications in electronics or tissue engineering. Surfaces of polyethyleneterephthalate and polytetrafluoroethylene were modified by plasma discharge and subsequently, grafted with 2-mercaptoethanol, 4,4′-biphenyldithiol, and cysteamine. The thiols are expected to be fixed via one of –OH, –SH or –NH₂ groups to reactive places on the polymer surface created by the plasma treatment. “Free” –SH groups are allowed to interact (graft) with gold nanoparticles and nanorods. Gold nano-objects were characterized before grafting by transmission electron microscopy and UV–Vis spectroscopy. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and electrokinetic analysis (zeta potential determination) were used for the characterization of polymer surface at different modification phases. It was proved by FTIR and XPS measurements that the thiols were chemically bonded on the surface of the plasma-treated polymers, and they mediate subsequent grafting of the gold nano-objects. On the surfaces, modified polymers were indicated some objects by AFM, size of which was dramatically larger in comparison with that of original nanoparticles and nanorods. This result and the other results of UV–Vis spectroscopy indicate an aggregation of deposited gold nano-objects.     

Polymer brushes on carbon nanotubes by thiol-lactam initiated radical polymerization of 2-hydroxyethyl methacrylate

Water-soluble polymer brushes with multi-walled carbon nanotubes (MWNTs) as backbones were synthesized by grafting 2-hydroxyethyl methacrylate (HEMA) from surface functionalized MWNTs via in situ surface thiol-lactam initiated radical polymerization. MWNTs were functionalized with 2-mercaptoethanol and used as initiators in the polymerization of HEMA in the presence of butyrolactam. FT-IR, XPS, 1H NMR, GPC and TGA were used to determine chemical structure and the grafted polymer quantities of the resulting product. The covalent bonding of PHEMA to the MWNTs dramatically improved the water dispersibility of MWNTs. The average thicknesses of the polymer brushes in the functionalized MWNTs were detected with electron microscopy (SEM and TEM) and images indicated that the nanotubes were coated with polymer layer.     

Grafting of polymers from clay nanoparticles via high-dose gamma-ray irradiation

In this work, the prepared mixture of low concentration of ethyl acrylate (EA) monomers and organophilic montmorillonite (OMMT) particles in methanol solution was exposed to gamma-ray (γ-ray) irradiation. It was found that EA monomers first polymerized at relatively low radiation dose (< 10 kGy), then the polymerized PEA chains can graft onto the OMMT particles when the radiation dose increases above 185 kGy. Electron spin resonance (ESR) tests verified that a large amount of radicals could be created on PEA chains and the OMMT particles at high radiation dose. When the radicals on the PEA chains combined with the radicals on the surface of silicate layers of OMMT particles, the grafting reaction took place. Furthermore, Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) results all confirmed the presence of PEA grafting on the surface of the stacking silicate layers of OMMT particles.     

Polymer microspheres stabilized by titania nanoparticles

Polymer microspheres stabilized by titania nanoparticles were synthesized using a two-step Pickering emulsion polymerization process, in which nanosized titania nanoparticles were used as solid emulsifiers and building blocks. It gives a simple but novel route for the fabrication of functional inorganic/polymer hybrid materials with controlled microstructures. The final Pickering emulsion can be applied to various substrates forming continuous films with highly ordered nanosized to microsized TiO₂ protuberances across the films. Those films will have potential applications for photo-catalyst, water and air purification.     

Grafting of poly(ethylene glycol) monoacrylates on polycarbonateurethane by UV initiated polymerization for improving hemocompatibility

Poly(ethylene glycol) monoacrylates (PEGMAs) with a molecular weight between 400 and 1,000 g mol^?1 were grafted by ultraviolet initiated photopolymerization on the surface of polycarbonateurethane (PCU) for increasing its hydrophilicity and improving its hemocompatibility. The surface-grafted PCU films were characterized by Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy, water contact angle, scanning electron microscopy (SEM) and atomic force microscopy measurements. The surface properties of the modified films were studied in dry and wetted state. Blood compatibility of the surfaces was evaluated by platelet adhesion tests and adhered platelets were determined by SEM. The results showed that the hydrophilicity of the films had been increased significantly by grafting PEGMAs, and platelets adhesion onto the film surface was obviously suppressed. Furthermore, the molecular weight of PEGMAs had a great effect on the hydrophilicity and hemocompatibility of the PCU films after surface modification and increased with increasing molecular weight of PEGMAs.     

Facilely dispersible magnetic nanoparticles prepared by a surface-initiated atom transfer radical polymerization

Facilely dispersible magnetic nanoparticles (Fe₃O₄) prepared by a surface-initiated atom transfer radical polymerization (ATRP) of poly (ethylene glycol) methyl ether monomethacrylate (PEGMA) are reported. The initiator of 2-bromoisobutyrate (BIB) for ATRP was immobilized onto the surface of Fe₃O₄ nanoparticles by the reaction between 2-bromoisobutyryl bromide (BIBB) and the hydroxyl group on the nanoparticles. The results indicated that the poly(poly(ethylene glycol) monomethacrylate) (PPEGMA) was successfully grafted onto the surface of the magnetic nanoparticles. The core-shell nanoparticles with particle size of ≈ 20 nm in water (about 20 mg/mL) are facilely dispersible and can be easily captured by a magnet with magnetic field of 2000 G.     

乙基纤维素接枝偶氮苯聚合物的合成与研究

通过原子转移自由基聚合(ATRP)技术合成乙基纤维素接枝偶氮苯聚合物.以功能化乙基纤维素作为大分子引发剂,在CuBr/N,N,N′,N″,N″-五甲基二亚乙基三胺(PMDETA)催化体系下,以苯甲醚为溶剂,引发对甲氧基偶氮苯单体6-[4-(4-甲氧基苯基偶氮)酚氧基]己基甲基丙烯酸酯(MMAzo)的ATRP反应,构筑接枝共聚物.通过多种手段接枝共聚物结构、热行为与液晶性进行表征.接枝共聚物在紫外-可见光照射下发生可逆的顺反异构化反应,具有作为光学材料的潜力.     

Vacuum electric discharge initiated by accelerated nanoparticles

A static breakdown induced by the impact of particles detached from a point anode in a strong electric field, corresponding to the athermal field evaporation threshold, was studied by field ion microscopy. Under these conditions, the particle size threshold for the vacuum discharge initiation decreases by one order of magnitude as compared to the case of flat electrodes and falls within a nanometer range of the average radius of bombarding charged particles. The threshold energies of particles initiating a static electric discharge also exhibit a significant decrease.     

Preparation of poly(MAA-g-EG) hydrogel nanoparticles by a thermally-initiated free radical dispersion polymerization

Poly(methacrylic acid-grafted-poly(ethylene glycol)) (P(MAA-g-EG)) hydrogel nanoparticles (HNPs) were prepared by a thermally-initiated free radical dispersion polymerization method. The effects of various reaction parameters on the preparation of HNPs were investigated, including the quantity of monomer, temperature, initiator dosage, crosslinker dosage, and co-stabilizer concentration. The reaction temperature at 75 degrees C was found to be suitable for preparing stable and small P(MAA-g-EG) HNPs. By adding a little amount of polyvinyl alcohol in the reaction media, P(MAA-g-EG) HNPs with narrow size distribution could be obtained. The effects of pH and the crosslinker dosage on the equilibrium swelling behavior of P(MAA-g-EG) HNPs were also studied. The P(MAA-g-EG) HNPs perform pH-responsive swelling behavior, which is strongly influenced by the crosslinker dosage.     

Photocross-linking of polymers initiated by benzylsulphonium salts as cationic initiators

Photocross-linking behaviour of poly(ethylene-co-glycidyl methacrylate) (EGMA) initiated by benzylsulphonium slats (BSS) has been investigated in relation to negative photoresist. Unlike triarylsulphonium slats which produce Brønsted acids, following the reaction with solvents or monomers, BSS directly produces benzyl cation on photoirradiation at > 300 nm and the resulting benzyl cation attacks the epoxy residues in EGMA to initiate cationic polymerization, leading to interchain cross-linking of the polymer. In this photocross-linking reaction, the efficiency was found to be so high that only 0.15 mol% BSS (based on the epoxy content in the copolymer) was enough to produce an insoluble network of the copolymer. This fact strongly suggests the presence of domains where the epoxy moieties and BSS are concentrated, thereby once initiating species (benzyl cation) are formed photochemically, the cationic polymerization takes place effectively in these domains.     

Photocross-linking of polymers initiated by benzylsulphonium salts as cationic initiators

Photocross-linking of poly(1,3-dioxolane-4-methyl methacrylate) and copolymers with methyl methacrylate initiated by benzylsulphonium salt (BSS) has been explored. On photoirradiation, BSS directly produces benzyl cations which are capable of initiating cationic polymerization of side-chain cyclic ketals. The homopolymer and the copolymers were doped with BSS in the concentration range 0.05–5 mol % on the basis of the ketal units and the resulting films were irradiated at > 300 nm in air. The course of the photocross-linking of the sample films was followed spectroscopically by measuring the absorbance due to BSS (ultraviolet) and the absorbance due to dioxolane (infrared) as well as thermal analysis (differential scanning calorimetry) and chemical titration (ketal content). It was found that BSS is effective in inducing the cross-linking of the polymers, and the present system might be a promising candidate for a highly sensitive negative photoresist with an aqueous developing system.     

Surface functionalization of biomaterials by radical polymerization

One effective strategy in the field of biomaterials is to develop biomimetic interfaces to modulate the cell behavior and promote tissue regeneration and surface modification is the best way to obtain biomaterial surfaces with the desired biological functions and properties. Surface radical polymerization offers many advantages compared to other methods, for instance, low cost and simplicity, ability to control the surface chemistry without changing the properties of the bulk materials by introducing high-density graft chains and precisely controlling the location of the chains grafted to the surface, as well as long-term chemical stability of the chains introduced by this method due to the covalent bonding. Because of the precise control of the macromolecules and easy preparation, controlled/living radical polymerization has been widely used to modify biomaterials. There are three main techniques: atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), and reversible radical addition-fragmentation chain transfer (RAFT) polymerization. Some other grafting methods such as plasma-induced polymerization, irradiation-induced polymerization, and photo-induced polymerization also have great potential pertaining to functionalization of biomaterials and tailoring of surface chemistry. This paper summarizes recent advances in the various grafting polymerization methods to enhance the surface properties and biological functions of biomaterials.     

Surface initiated atom transfer radical polymerization: access to three dimensional wavelike polymer structure modified capillary columns for online phosphopeptide enrichment

Reversible phosphorylation is one of the most important post-translational modifications of proteins and a key regulator of cellular signaling pathways. Specific enrichment of phosphopeptides from proteolytic digests is a prerequisite for large scale identification of protein phosphorylation by mass spectrometry. Online enrichment of phosphopeptides attracts particular interests due to its automated operation, higher throughput and reproducibility, lower sample loss, and contamination. Here, we report a new type of capillary column developed using surface initiated atom transfer radical polymerization (SI-ATRP) for automated online phosphopeptide enrichment. SI-ATRP modification leads to a surface confined growth of three-dimensional wavelike polymer structure on the inner wall of capillary columns and, therefore, results in largely increased surface area. Furthermore, the noncross-linked flexible polymer chains grown by SI-ATRP create a large internal volume that allows phosphopeptides to penetrate into during enrichment and also facilitate the interaction between the numerous functional groups in the polymer chains and target phosphopeptides. Therefore, highly efficient and specific enrichment is achieved even for a low femtomole of phosphopeptides. The loading capacity is increased more than an order of magnitude compared with that obtained using conventional open tubular capillary columns. The SI-ATRP modified capillary column was successful applied in the online phosphoproteomics analysis of HepG2 cell lysate and resulted in 10 times improved phosphopeptide identification than the previously reported number. Finally, the SI-ATRP technique is compatible with a variety of functional monomers, and therefore, versatile potential applications in reverse phase, ion exchange, and affinity chromatography can be expected.     

Surface-initiated atom transfer radical polymerization of methyl methacrylate from magnetite nanoparticles at ambient temperature

The synthesis of methyl methacrylate (MMA) brush from the surface of magnetite nanoparticles (core-shell structure), from initiator moieties anchored covalently to the nanoparticles, via room temperature atom transfer radical polymerization (ATRP) is described. The surface-initiated polymerization was carried out from a surface-confined initiator containing a 2-bromoisobutyrate moiety with Cu(I)Br/PMDETA catalytic system. The initiator moiety was covalently anchored to the nanoparticles via a two step modification reaction scheme. Controlled polymerization was observed if ethyl-2-bromoisobutyrate (2-EiBrB) was added as a free/sacrificial initiator. A linear increase of molecular weight and a narrow molecular weight distribution of the PMMA formed in solution, provide evidence for a controlled surface-initiated polymerization, leading to surface-attached polymer brushes under mild conditions. The grafted PMMA provides good stability and dispersibility for the nanoparticles in organic solvents.     

Controlled fabrication of theophylline imprinted polymers on multiwalled carbon nanotubes via atom transfer radical polymerization

Theophylline imprinted polymers were synthesized on the surface of multiwalled carbon nanotubes via atom transfer radical polymerization using brominated multiwalled carbon nanotubes as an initiator. The nanotube-based initiator was prepared by directly reacting acyl chloride-modified multiwalled carbon nanotubes with 2-hydroxylethyl-2'-bromoisobutyrate. The grafting copolymerization of 2-hydroxyethyl-2-methyl-2-propenoate and ethylene glycol dimethacrylate in the presence of template theophylline led to thin molecularly imprinted polymer films coating multiwalled carbon nanotubes. The thickness of molecularly imprinted polymer films prepared in this study was about 5 nm as determined by transmission electron microscopy. Fourier-transform infrared spectroscopy was utilized to follow the introduction of initiator groups as well as polymers on the carbon nanotube surfaces. Thermogravimetric analysis indicated that the molecularly imprinted polymers were successfully grown from the carbon nanotube surfaces, with the final products having a polymer weight percentage of ca. 50 wt%. The adsorption properties, such as adsorption dynamics, special binding and selective recognition capacity, of the as-prepared molecularly imprinted polymer films were evaluated. The results demonstrated that the composite of molecularly imprinted polymers and multiwalled carbon nanotubes not only possessed a rapid dynamics but also exhibited a good selectivity toward theophylline, compared to caffeine.     

Preparation of pH-responsive silver nanoparticles by RAFT polymerization

Silver nanoparticles were prepared by chemical reduction of AgNO₃ in the presence of the PDMAEMA-b-PPA, which was synthesized by the reversible addition-fragmentation transfer technique. The formation of the silver nanoparticles was determined by the transmission electron microscopy (TEM) images and UV–Vis absorption spectra. The average size of the silver nanoparticles was shown to 11.4 nm. Particularly, the pH-responsive property of the silver nanoparticle was further observed. It was characterized by the zate potential, the UV–Vis spectra, and TEM images. The results show that the pH-responsive property is attributed to the aggregate of the silver nanoparticles as a function of pH. The characteristic is expected to apply in the nanoscale optical biosensor and biomaterials.     

Fabrication of pure ZnO nanoparticles by polymerization method

ZnO nanoparticles have received enormous attention due to their wide range of application such as diodes, ultraviolet-protection films, catalysts, sensors, ceramics and solar energy transformation parts. In the current research, ZnO nanoparticles were prepared by polymer decomposition. Synthesized ZnO nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and transition electron microscopy (TEM) and size distribution of these particles was investigated. Narrow size distribution of particles with a diameter of 20–30 nm and the regular distribution of ZnO nanoparticles were attributed to the application of poly amidoxime polymer. The results show that the polymer thermal decomposition technique is a feasible method for production of ZnO nanoparticles.     

Thermally induced structural evolution of methylsilicone xerogel monoliths reinforced by titania nanoparticles

Thermally stable methylsilicone xerogel monoliths were prepared by sol–gel technology with methylsilicone oligomer as precursor and titania nanoparticles as filler. The effects of titania doping and heating temperature on the structure, morphology, and hydrophobic property of xerogels were investigated. The structural evolution under thermal treatment showed that the blank methylsilicone monolith was crushed after 300 °C treatment, but the samples reinforced by titania could retain the intact structure after 500 °C treatment. Thermogravimetric analysis results certified that the thermal degradation of methylsilicone was resisted due to incorporation of TiO₂. Fourier transform infrared spectra and ²⁹Si nuclear magnetic resonance results showed that Si–CH₃ unit still existed in the reinforced samples, compared with the complete transformation of Si–C to Si–O in the blank methylsilicone after 500 °C treatment. Thus, the hydrophobic property was preserved and certified by measurement of contact angle.     

Effects of oxygen on the properties of titania nanoparticles prepared by MOCVD

Anatase titania nanoparticles are prepared using pyrolysis of titanium tetrabutoxide in oxygen free and oxygen containing atmospheres by MOCVD method. Influence of oxygen on the properties of the titania nanoparticles is investigated, followed by discussion. The results show that oxygen influences not only the particle size but also the particle size distribution of the nanoparticles. With increasing oxygen flow rates, the average grain sizes of the nanoparticles decrease and the particle size distributions become uniform. Oxygen exerts great influence on the nucleation rate of the nanoparticles and reaction kinetics occurred in the reactor. The formation of titania nanaoparticles by MOCVD is not a growth controlled process, but is a nucleation rate controlled process.     

Mechanochemical polymerization of styrene initiated by the grinding of layered clay minerals

The polymerization of styrene mechanochemically initiated by the grinding of talc was performed by using a vibrating ball mill. Talc used was one of layered clay minerals as well as montmorillonite. The effect of the grinding of talc on the polymerization of the styrene was investigated by characterizing the polymer formed and talc ground. The results revealed that of all the experiments we have performed thus far, styrene most abundantly polymerized by grinding of talc. The polymerization of styrene was closely related to the total surface area of the ground talc. The products obtained were the composites of talc particles and resulting polymer attached to the particle surface. From the analysis of the molecular weight distribution of the polymer, it was suggested that the polymerization of the styrene proceeded with two types of cationic active species which were produced by the grinding of layered clay minerals. Mechanochemical polymerization is expected to be one of the more promising production processes of polymeric nanocomposites when layered clay minerals can be ground to finer nanometer sized-particles.