Summary: A water‐soluble gold nanoparticle aggregate 2 was prepared by chloroauric acid and a polypseudorotaxane 1 of mono‐6‐thio‐β‐cyclodextrin with poly(propylene glycol) bis(2‐aminopropyl ether) ( ≈ 2 000) in the presence of sodium borohydride in N,N‐dimethylformamide (DMF) solution. The investigative results indicated that the gold nanoparticle aggregate 2 might act as an efficient DNA‐cleavage reagent.
A typical TEM image of gold nanoparticle aggregate 2 . 相似文献
Summary: The vapor‐based synthesis and characterization of a reactive polymer, poly[(4‐formyl‐p‐xylylene)‐co‐(p‐xylylene)] ( 1 ), have been reported. The reactive polymer coating enables the immobilization of oligosaccharides via the chemoselective aldehyde‐hydrazide coupling reaction.
Highly dispersed ZnO nanoparticles with variable particle sizes were successfully prepared within an amphiphilic hyperbranched polyetherpolyol matrix via decomposition of an organometallic precursor in the presence of air leading to stable nanocomposites. The high degree of stabilization during and after the synthesis by the polymer permits control over the nanoparticle size and therefore, due to the quantum‐size‐effect, the particle properties. Furthermore, these polymer‐inorganic nanocomposites can easily be dispersed in apolar solvents to yield highly transparent, stable solutions.
A novel self‐oscillating gel actuator with gradient structure, which generates a pendulum motion by fixing one edge of the gel without external stimuli was achieved. The gel was synthesized by copolymerizing the ruthenium catalyst for the Belousov‐Zhabotinsky reaction with N‐isopropylacrylamide and 2‐acrylamido‐2‐methylpropane sulfonic acid. Furthermore, we clarified that the period and amplitude for the self‐oscillating behavior of the gel actuator are controllable by changing the composition, temperature, and size of the gel. The maximum amplitude of the novel gel actuator is about a 100 times larger than that of the conventional self‐oscillating gel system.
A generalized silica coating scheme is used to functionalize and protect sub‐micron and micron size dicyclopentadiene monomer‐filled capsules and polymer‐protected Grubbs' catalyst particles. These capsules and particles are used for self‐healing of microscale damage in an epoxy‐based polymer. The silica layer both protects the capsules and particles, and limits their aggregation when added to an epoxy matrix, enabling the capsules and particles to be dispersed at high concentrations with little loss of reactivity.
Precise nano‐ and microscale control of the architecture of biodegradable biomaterials is desirable for several biotechnological applications such as drug delivery, diagnostics, and medical imaging. Herein, we combine electrohydrodynamic co‐jetting and highly specific surface modification (via Huisgen 1,3‐dipolar cycloaddition) to prepare particles and fibers with spatioselective surface modification. We first prepared biphasic particles and fibers from commercial poly(lactide‐co‐glycolide) copolymers via electrohydrodynamic co‐jetting of two organic solutions loaded with fluorescent macromolecules and acetylene‐modified PLGA derivatives. (i) Spatially controlled reaction of poly[lactide‐co‐(propargyl glycolide)] with O‐(2‐aminoethyl)‐O′‐(2‐azidoethyl)heptaethylene glycol and (ii) subsequent conversion of the newly introduced amino groups with fluorescence probes resulted in particles and fibers with surface modification of one hemisphere only.
Nonlinear optical vinyl polymers with high glass transition temperature (Tg) were prepared by the functionalization of a fluorinated acrylate‐methyl vinyl isocyanate copolymer. A modified pathway to obtain a thiophene bridged chromophore was worked out. Poled films of the polymers show a fairly high and stable nonlinear optical response, even at elevated temperatures.
The thiophene‐bridged chromophore, based on a substituted dicyanomethylene‐dihydrofuran acceptor, synthesized here. 相似文献
We report a simple procedure to prepare a novel Au‐micelle composite with a core‐shell‐corona structure. This composite is prepared by reduction of tetrachloroauric acid (HAuCl4 · 3H2O) in dilute aqueous solution containing polystyrene‐block‐poly(4‐vinylpyridine) micelles and poly(ethylene oxide)‐block‐poly(4‐vinylpyridine) copolymers. The micelles with a polystyrene core and a poly(4‐vinylpyridine) shell are transformed into Au‐micelle composites with a polystyrene core, a swollen hybrid Au/poly(4‐vinylpyridine) inner shell, and a poly(ethylene oxide) corona by direct physisorption of gold particles with poly(4‐vinylpyridine) chains.
Enzymatic grafting of caprolactone was carried out from poly[styrene‐co‐(4‐vinylbenzyl alcohol)] containing 10% hydroxyl functional monomer and compared with the grafting of vinyl acetate. A molecular weight increase due to the grafting of polycaprolactone was observed by size exclusion chromatography. Closer investigation of the grafting density by 1H NMR revealed an upper limit to the amount of grafting of about 50–60% of the pendant hydroxyl groups leaving unreacted hydroxyl groups on the polymer backbone available for subsequent reactions. The higher grafting density (95%) obtained with vinyl acetate suggests that this is not due to limited accessibility of the backbone but sterical constrains. Moreover, the grafting action of polycaprolactone seems to be a combination of grafting from by monomer initiation and grafting onto by transesterification of polycaprolactone.
A numerical model is presented for the optimal vulcanization of 2D extruded polar rubber with microwaves and peroxides. Magnetron power and curing time are used as the input production parameters, and the output mechanical property selected for optimization is the average tensile strength of the item. A 2D thick weather strip is analyzed to validate the model. The electric field is evaluated by means of Yee cells (FDTD approach) and suitably inserted in Fourier's heat transmission law, thus allowing point‐by‐point temperature profiles to be determined. The temperature is then used to evaluate the degree of peroxidic reticulation, and thus the final tensile strength. A so‐called alternating tangent approach based on the bisection method is finally proposed to estimate the optimal magnetron power and curing time.
Summary: A diblock copolymer brush consisting of poly(methyl acrylate)‐block‐poly(pentafluoropropyl acrylate) (Si/SiO2//PMA‐b‐PPFA) was synthesized on a porous silica substrate. The brush was exposed to selective solvents, as well as thermal treatments, to induce a surface rearrangement. The rearrangement resulted in the selective loss or creation of an ultrahydrophobic layer by location of the fluoropolymer segment. This work demonstrates that surface rearrangements observed on flat surfaces can be transferred to porous substrates.
Image of a water droplet in contact with an Si/SiO2//PMA‐b‐PPFA ultrahydrophobic polymer brush, synthesized from a porous silica substrate. 相似文献
A linear variable differential transformer (LVDT) was employed to evaluate CO2‐polymer plasticization. Preliminary results on polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) elastomer are presented. At 22 °C under CO2 pressure, SBS undergoes compression due to hydrostatic pressure. However, sample expansion occurs upon depressurization. At 45 °C, SBS undergoes swelling of 0.7% due to CO2 plasticization, while no post‐pressurization expansion is observed. The contrasting result is explained by change in PS domain mobility and discontinuity in the density‐pressure relationship.
Linear displacement of SBS as a function of time at 56 and 134 bar CO2. 相似文献
Well‐dispersed silver nanoparticles were successfully fabricated within poly[(N‐isopropylacrylamide)‐co‐(acrylic acid)] [P(NIPAM‐co‐AA)] microgel particles which were synthesized with different cross‐linking densities. Their structures were studied by field‐emission scanning electron microscopy, transmission electron microscopy, UV‐vis spectroscopy, X‐ray diffraction and FT‐IR spectroscopy. The interactions between the microgel particles and the incorporated silver nanoparticles were investigated by X‐ray photoelectron spectroscopy. The results revealed that there was charge transfer from the carbonyl groups of the microgel particles to the silver nanoparticles. Moreover, as the diameter of the AgNPs decreases, the charge‐transfer efficiency increases accordingly. The P(NIPAM‐co‐AA)/AgNPs hybrid microgel particles were thermoresponsive and their behavior completely reversible with several heating/cooling cycles.
Summary: Self‐oscillating polymers and nano‐gel particles consisting of N‐isopropylacrylamide and the ruthenium catalyst of the Belousov‐Zhabotinsky reaction have been prepared. In order to clarify the crosslinking effect on the self‐oscillating behavior, the phase transition behaviors were investigated by measuring the transmittance and the fluorescence intensity of the polymer solution and the gel bead suspension. Cooperative effects due to crosslinking will play an important role for the design of nanoactuators.
Chemical structure of poly(NIPAAm‐co‐Ru(bpy)3). 相似文献
New luminescent electrospun (ES) fibers for pH‐tunable colorimetric sensors were prepared from binary blends of poly(phenylquinoline)‐block‐polystyrene (PPQ‐b‐PS)/polystyrene (PS) with a single‐capillary spinneret. The PPQ‐b‐PS aggregated domain sizes in the ES fibers prepared from dichloromethane (CH2Cl2), chlorobenzene (CB) and chloroform (CHCl3) were 1.5 ± 0.5, 2.2 ± 0.4 and 4.1 ± 1.1 µm, respectively. Such variation on the aggregation size led to the red‐shifting photoluminescence spectra changing from green, to yellow, and orange. ES fibers prepared from CH2Cl2 exhibited pH‐tunable photoluminescence and the emission maximum varied from 532 to 560 nm as the pH value changed from 7 to 1. The study demonstrated that the ES fibers prepared could have potential applications for sensory devices.
We report for the first time the preparation of single polypyrrole (PPy) molecule chains using a “metal‐organic framework” with 1 nm channels as a template. The obtained one‐dimensional (1‐D) PPy has highly structure order and excellent conductivity, which has improved by as much as five orders of magnitude in comparison with that of 2‐D PPy.
Low‐molecular weight amphiphilic diblock copolymers, polystyrene‐block‐poly (2‐vinylpyridine) (PS‐b‐P2VP), and (P2VP‐b‐PS) with different block ratios were synthesized for the first time via organotellurium‐mediated living radical polymerization (TERP). For both the homo‐ and block copolymerizations, good agreement between the theoretical, and experimental molecular weights was found with nearly 100% yield in every case. The molecular weight distribution for all the samples ranged between 1.10 and 1.24, which is well below the theoretical lower limit of 1.50 for a conventional free radical polymerization. Furthermore, a very simple approach to producing highly dense arrays of titania nanoparticles (TiO2) is presented using a site‐selective reaction of titanium tetraisopropoxide within the P2VP domains of micellar film of P2VP‐b‐PS in toluene through the sol–gel method.
Poly(N‐isopropylacrylamide)‐block‐poly{6‐[4‐(4‐pyridyazo)phenoxy] hexylmethacrylate} (PNIPAM‐b‐PAzPy) was synthesized by successive reversible addition‐fragmentation chain transfer (RAFT) polymerization. In a water/tetrahydrofuran (H2O/THF) mixture, amphiphilic PNIPAM‐b‐PAzPy self‐assembles into giant micro‐vesicles. Upon alternate ultraviolet (UV) and visible light irradiation, obvious reversible swelling‐shrinking of the vesicles was observed directly under an optical microscope. The maximum percentage increase in volume, caused by the UV light, reached 17%. Moreover, the swelling could be adjusted using the UV light power density. The derivation of this effect is due to photoinduced reversible isomerization of azopyridine units in the vesicles.
We demonstrate spatially controlled photoreactions within bicompartmental microparticles and microfibers. Selective photoreactions are achieved by anisotropic incorporation of photocrosslinkable poly(vinyl cinnamate) in one compartment of either colloids or microfibers. Prior to photoreaction, bicompartmental particles, and fibers were prepared by EHD co‐jetting of two compositionally distinct polymer solutions. Physical and chemical anisotropy was confirmed by confocal laser scanning microscopy, Fourier‐transformed infrared spectroscopy, and scanning electron microscopy. The data indicate adjustment of polymer concentrations of the jetting solutions to be the determining factors for particle and fiber structures. Subsequent exposure of poly(vinyl cinnamate)‐based particles and fibers to UV light at 254 nm resulted in spatially controlled crosslinking. Treatment of the crosslinked bicompartmental colloids with chloroform produced half‐moon shaped objects. These hemishells exhibited a distinct porous morphology with pore sizes in the range of 70 nm. Based on this novel synthetic approach, Janus‐type particles and fibers can be prepared by EHD co‐jetting and can be selectively photocrosslinked without the need for masks or selective laser writing.
A series of poly{(3‐hexylthiophene)‐co‐[3‐(6‐hydroxyhexyl)thiophene]}:titania (P3HT‐OH:TiO2) hybrids were synthesized via the in situ polycondensation of titanium (IV) n‐butoxide in the presence of P3HT‐OH. Introducing a hydroxyl moiety onto the side‐chain of poly(3‐hexylthiophene) (P3HT) significantly promotes the polymer‐titania interaction, resulting in the formation of homogeneous hybrid colloids. The UV‐vis spectra of P3HT‐OH:TiO2 films demonstrate that TiO2 markedly affects the stacking structure and the chain conformation of P3HT‐OH. The maximum absorption wavelength of these hybrid materials can be tailor‐made by merely varying the weight percentage of TiO2. Moreover, P3HT‐OH:TiO2 can be further utilized as an efficient compatibilizer in preparing photoactive P3HT:P3HT‐OH:TiO2 films with excellent miscibility. The photovoltaic cell based on such a hybrid exhibited a 2.4‐fold higher value of power‐conversion efficiency compared to the cell based on P3HT:TiO2.
