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
Polymeric core–shell microstructures have been constructed through a new method, namely sequential precipitation, which is intrinsically a self‐assembly and phase separation process. High‐quality poly(vinyldene fluoride)–polycarbonate–lithium perchlorate composite films with spherical core–shell microstructures have been prepared and determined to consist of conducting cores and insulating shells. Because of the percolation effect, the resulting materials present a dielectric constant as high as 104–107 at the threshold.
Blue emission of oxygen‐doped tertiary amine (triethylamine), a key unit of fluorescent poly(amido amine) dendrimer, was demonstrated. It was found that the fluorescence intensity could be further enhanced if the tertiary amines locate densely in the dendrimer interior as the branching sites. Moreover, a solvatochromic phenol blue, instead of oxygen, is able to induce the blue fluorescence of the tertiary amino‐branching sites based on a guaranteed host‐guest complexation of phenol blue molecules and dendrimer interior.
An amphiphilic biodegradable polymer, poly(aspartic acid‐co‐lactic acid) (PAL), was synthesized by simply heating a mixture of aspartic acid (Asp) and L ‐lactide without additional catalysts or solvents. The unique branched architecture comprising succinimide units and lactic acid units was confirmed by IR and NMR spectroscopy. A copolymer of sodium aspartate and lactic acid (PALNa) was prepared by reacting PAL with an aqueous sodium hydroxide solution. The PAL was soluble in many organic solvents, while the PALNa was soluble in methanol and water. The hydrolytic degradation behavior of PAL varied with the copolymer composition. A higher Asp content resulted in a faster molecular weight decrease, and introducing glycolic acid units accelerated the degradation rate.
Summary: The debate on the mechanism of dithiobenzoate‐mediated RAFT polymerization may be resolved by including the reaction between a propagating radical and the star‐shaped combination product from irreversible termination into the kinetic scheme. By this step, a highly reactive propagating radical and a not overly stable three‐arm star species are transformed into the resonance‐stabilized RAFT intermediate radical and a very stable polymer molecule. The time evolution of concentrations is discussed for the main‐equilibrium range of CDB‐mediated methyl acrylate polymerization.
Illustration of the novel understanding of the RAFT mechanism in dithiobenzoate‐mediated RAFT polymerization. 相似文献
CdSe nanoparticles stabilized with the amphiphilic diblock copolymer polystyrene‐block‐poly(4‐vinylpyridine) were spread from toluene dispersion on the water surface. Monolayers could be transferred onto solid substrates using the Langmuir‐Blodgett technique. By means of atomic force and scanning electron microscopy highly symmetric ring and disk‐like structures with diameters ranging between 150 nm and 1200 nm were observed.
AFM image of a mixed monolayer of copolymer 12 and CdSe nanoparticles stabilized with polystyrene‐block‐poly(4‐vinylpyridine). 相似文献
A novel chlorotitanium calix[4]arene complex was synthesized and tested, without activator, as catalyst for the polymerization of L ‐ and rac‐lactide under solvent‐free conditions. The catalyst displayed high activity, which depended on the monomer‐to‐catalyst molar ratio, and led to highly isotactic PLLA. Despite concomitant transesterification during the polymerization, polylactide formation was well‐controlled, the molar mass distribution indexes remaining in the restricted range of 1.2–1.4.
A novel preparation method for the core‐shell type biodegradable polyesters or biodegradable materials grafted with biodegradable polyesters was developed by alkaline surface treatment of biodegradable polyester films and subsequent enzymatic polymerization of aliphatic lactones, one example of which is shown in this study, i.e., the preparation of poly(L ‐lactide) (PLLA) film grafted with poly(ε‐caprolactone). It is revealed that only alkaline surface treatment or the combination of alkaline surface treatment and enzyme‐catalyzed grafting, the former and the latter, respectively accelerating and delaying the enzymatic degradation of PLLA, will give PLLA materials having a wide variety of biodegradability. Also, the specificity of the enzyme used for hydrolysis could be used to confirm the grafted chain species.
A novel comb‐like derivative CPEG‐g‐DNQ was prepared by incorporating light responsive 2‐diazo‐1,2‐naphthoquinone (DNQ) groups into the structure of comb‐like poly(ethylene glycol) (CPEG). DLS and TEM results showed that CPEG‐g‐DNQ self‐assembled into spherical micelles with an average size of about 135 nm in water. Upon exposure to light, the micelles could be disrupted because of the conversion of hydrophobic DNQ to hydrophilic 3‐indenecarboylic acid. Additionally, hydrophobic coumarin 102 was successfully loaded into the micelles and photo‐induced ON‐OFF release was demonstrated by fluorescence spectroscopy. MTT assay revealed that the micelles are biocompatible. These photo‐responsive micelles might have great potential for controlled release of hydrophobic drugs.
Summary: An initiator for nitroxide mediated ‘living’ free radical polymerization was prepared with a fluorescent tag attached to the initiating alkyl radical terminus. This was used to synthesize amphiphilic poly(acrylic acid)‐block‐polystyrene diblock copolymers, which self assembled in a tetrahydrofuran/buffer solution to form structures that are visible by fluorescence.
The proteins of eggshell membranes, an industrial waste product, are dissolved by reductive cleavage with aqueous 3‐mercaptopropionic acid and acetic acid. The soluble protein preparation is cast into a thin film, and its bioactivity is investigated by cell culture.
Photomicrograph of NIH3T3 fibroblasts cultured on SEP film for 3 days. 相似文献
A set of poly(propylene) composites containing different amounts of copper nanoparticles (CNP) were prepared by the melt mixed method and their antimicrobial behavior was quantitatively studied. The time needed to reduce the bacteria to 50% dropped to half with only 1 v/v % of CNP, compared to the polymer without CNP. After 4 h, this composite killed more than 99.9% of the bacteria. The biocide kinetics can be controlled by the nanofiller content; composites with CNP concentrations higher than 10 v/v % eliminated 99% of the bacteria in less than 2 h. X‐ray photoelectron spectroscopy did not detect CNP at the surface, therefore the biocide behavior was attributed to copper in the bulk of the composite.
Via a batch process in an autoclave, the foam processing of neat polylactide (PLA) and two different types of PLA/layered silicate nanocomposites has been conducted using supercritical carbon dioxide as a foaming agent. The morphological correlation between the dispersed silicate particles with nanometer dimensions in the bulk and the obtained closed‐cell structure of the foam is discussed. This is the first report that deals with the possibility of preparing biodegradable nanocellular polymeric foams via nanocomposite technology.
SEM image of the freeze‐fracture surface of a PLA/layered silicate foam, exhibiting closed‐cell structure. 相似文献
Summary: A new crystal morphology (δ form) of poly(3‐hydroxypropionate) (PHP) is found in cast and melt‐crystallized PHPs with low molecular weight, in which the PHP chains possibly adopt a 21 helix rather than the trans conformation found in the β or γ form. The fusion temperature‐ and the crystallization temperature‐dependent polymorphism are responsible for the dual morphologies and the unique growth kinetics of spherulites in the melt‐crystallized PHPs.
a) A dual‐morphology developed at 70 °C in PHP films after melting at 117 °C and b) that formed during cooling at a rate of 1 °C · min−1 from 130 °C. 相似文献
Composite films of poly(3,4‐ethylenedioxythiophene) (PEDOT)‐coated over functionalized multiwalled coiled and linear carbon nanotubes (CNTs) have been fabricated by a simple oxidative electropolymerization route. The nanotubular morphology of the polymer–CNT composite is responsible for the lower charge transfer impedance, lower internal resistance, and superior capacitive response in comparison to that shown by the control PEDOT film doped by trifluoromethanesulfonate ions. This facile electrochemistry exhibited by the PEDOT–CNT composite film ensues in a remarkably high coloration efficiency of 367 cm2 · C−1 at 550 nm, hitherto unrealized for PEDOT; thus demonstrating the huge potential the PEDOT–CNT composite film has as cathode for the entire spectrum of electrochromic devices.
The phase diagram of a series of poly(1,2‐octylene oxide)–poly(ethylene oxide) (POO–PEO) diblock copolymers is determined by small‐angle X‐ray scattering. The Flory–Huggins interaction parameter was measured by small‐angle neutron scattering. The phase diagram is highly asymmetric due to large conformational asymmetry that results from the hexyl side chains in the POO block. Non‐lamellar phases (hexagonal and gyroid) are observed near fPEO = 0.5, and the lamellar phase is observed for fPEO ≥ 0.5.
The synthesis of poly(N‐vinylcarbazole)‐based block copolymers functionalized with rhenium diimine complexes or pendant terpyridine ligands is reported. The copolymers are synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, and they exhibit interesting morphological properties as a result of the phase separation between different blocks. The rhenium complex polymer block may function as a photosensitizer, while the terpyridine‐containing polymer block can be used as the template for nanofabrication by selective deposition of zinc complexes.
Functional polymers possess tremendous potential both in academia and in industry. In particular, oxiranes offer manifold possibilities for the introduction of single hydroxyl or multiple orthogonal functionalities in carbanionic polymerization. Here, we present a brief overview of the fascinating possibilities arising from the employment of common as well as individually designed epoxide derivatives for the synthesis of end‐functional polymers. Continuous flow techniques can be utilized for the rapid generation and screening of precisely defined hydroxyl‐modified polymers. The utilization of functionalized polymers as precursors for the formation of complex macromolecular architectures (e.g., miktoarm star polymers) is summarized and potential applications as well as future perspectives are discussed.
In this paper, we report on the tunable metal‐enhanced fluorescence (MEF) of Ag nanostructures. Because of the good MEF properties of the highly dendritic Ag nanostructures, we obtained an increase of up to 25 times for the weak fluorescence of porphyrin molecules (Por4–). More importantly, by the introduction of a stimulus‐responsive PAA/PDDA multilayer film as an interlayer, the distance between the fluorophores and the Ag nanostructures could be tuned by immersing the substrates into solutions of different ionic strength or pH. The MEF behavior of the composite films could thus be tuned in a controlled manner, because of the distance dependent nature of the MEF effects.
