A stable aqueous solution of reduced graphene is prepared by chemical reduction of GO in the presence of PNIPAM in water through the hydrophobic interaction between graphene plates and PNIPAM backbones. Thermosensitive solubility switching of the graphene/PNIPAM assembly was successfully demonstrated below or above the LCST, which is higher (up to 42 °C) than the LCST of pure PNIPAM (36 °C) because interacting PNIPAM chains on graphene plates are less mobile than free PNIPAM chains. The success of PNIPAM as stabilizer for reduced graphene solution can be explained by both efficient hydrophobic interaction with graphene surface and matching of surface tension of water (72.8 mJ · m?2) with “graphene‐friendly surface tension” (40–50 mJ · m?2) by the presence of PNIPAM in water (41.8 mJ · m?2).
We present a new type of nanoporous hydroquinone/catechol formaldehyde resin synthesized by a one‐pot route, with a surface area of up to 1 112 m2 · g?1. The resins show highly efficient reactive adsorption for silver/gold (silver adsorbance up to 2.43 g · g?1) and excellent selectivity for gold (Kd is as high as 1 914 090 mL · g?1). The first‐used resins can be regenerated with NaHSO3, and the gold capacities of the recycled PCFR and PHFR reach 44 and 78% of their first loading capacities, respectively.
Summary: Four dendritic polyesters containing non‐linear optical chromophores on the periphery were synthesized and their material properties were compared for electro‐optic device applications. Thermal and optical parameters of the dendrimer materials were measured along with structural analysis. A high chromophore concentration in the dendritic polyesters produced enhancement of the optical non‐linearity. The second generation dendrimer (G1‐DAIDC) exhibited an electro‐optic coefficient of 43.4 pm · V?1 at 1.55 µm optical communication wavelength. Aromatic ester backbones elevate the glass transition temperature of the chromophore alignment, representing good thermal stability of the optical films.
Summary: Polymer blend nanocomposites containing linear low density polyethylene (LLDPE), nylon 6 and organoclays were prepared by melt mixing, and their morphologies and structures were examined with a field emission scanning electron microscope (FE‐SEM) and an X‐ray diffractometer (XRD). The size of phase‐separated domains decreased considerably with increasing content of organoclay. The d‐spacing of organoclay in the nanocomposites was increased from about 18.6 to over 28 Å. This effect was highly dependent on nylon 6 contents because nylon 6 is more polar and shows higher affinity to the organoclays compared to LLDPE.
A series of substituted fluorenes with vinyl groups as reactive sites were synthesized and characterized. Fluorene‐based polymers with vinyl groups as end chains and side chains functionalities were also prepared. In both cases, successful preparation of functionalized Parylene C films (modylayers) was achieved. The set of spectral methods used has allowed us to conclude that such functionalization is based on the chemical reaction of double bonds with xylylene radicals during deposition process. Parylene C films chemically modified with specially synthesized polyfluorenes showed PL quantum efficiency comparable with neat polyfluorenes.
Nail/spindle‐shaped polyaniline is synthesized by chemically oxidizing aniline with ammonium persulfate in a near‐neutral aqueous medium using PVP as the stabilizing agent. The type of dispersing agent, APS content and aniline concentration have obvious impacts on the morphology of the resulting polyaniline. Typically, in the concentration ranges of 1.5–6 × 10?4 M PVP and 0.02–0.05 M aniline and for molar ratios [APS]:[aniline] of 0.4:1 to 0.8:1, nail/spindle‐shaped polyaniline can be obtained. A possible mechanism is proposed to elucidate the formation process.
A bridged silsesquioxane was obtained from a precursor synthesized by the reaction of glycidoxypropyl(trimethoxysilane) (2 mol) with cyclohexylamine (1 mol). The polycondensation in the presence of formic acid produced a hybrid material exhibiting a short-range order based on elongated organic channels accommodating the pendant cyclohexyl fragments, bounded by inorganic domains. The presence of functional groups in the organic channels (tertiary amine, ether, hydroxyl), can be used to retain small organic molecules capable of forming hydrogen bonds. Aspirin was used as a probe to illustrate this possibility.
Three phosphorescent dendrimers ( IrC1 , IrC3 , and IrF2 ) with an iridium complex core and oligocarbazole or oligofluorene substituted ligands were synthesized and characterized. The structures of the oligocarbazole were designed to maintain high triplet energy of the ligands so that phosphorescence quenching in the resulting dendrimers can be prevented, while the oligofluorene in IrF2 resulted in undesired phosphorescence quenching. Best performance was obtained from an IrC3 based electrophosphorescent light‐emitting device with a maximum luminance of 13 060 cd · m?2 at a driving voltage of 11.5 V and a peak current‐efficiency of 4.3 cd · A?1 at a luminance of 3 400 cd · m?2, owing to its high PL efficiency, and efficient energy transfer between the iridium complex core and the ligands.
The polymerization of ethylene in the presence of 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediiminenickel(II) dichloride ( 1 ) and methylaluminoxane (MAO) gives hyperbranched polyethylene (HBPE) in appropriate reaction conditions. The system 1 /MAO is active in solvents like toluene or hexane at temperatures as high as 80 °C and ethylene pressures ranging from 1 to 15 atm. The polyethylenes obtained show high molecular weights (up to 467 kg · mol?1) and more than 218 branches per 1 000 backbone carbon atoms, qualifying these materials as hyperbranched. Dynamic‐mechanical thermal analysis (DMTA) of these materials shows high β‐transitions, directly related to the branch content of these polyethylenes.
DMTA analysis of polyethylenes obtained with 1 /MAO at 0, 30, and 50 °C (corresponding to entries 1, 2 and 3). 相似文献
Phenylphosphonic diisocyanate has been prepared and polymers from its condensation with hydrazines using the interfacial technique are reported. The polymers are believed to contain the following repeating structure: 相似文献
Summary: In this article we describe the synthesis of various monomers modified with triphenyl‐1,3,5‐triazine side groups as electron transport moieties. By nitroxide‐mediated polymerization with a TEMPO unimer it was possible to obtain polymers with a narrow polydispersity. Furthermore, by living radical polymerization block copolymers were obtained from these monomers. Therefore, microphase separated structures are accessible which possess hole conducting moieties in one phase and electron conducting moieties in the other phase.
General build‐up of the copolymers consisting of hole and electron conductor. 相似文献
Biodegradable and photocurable block copolymers of ε‐caprolactone and L ‐lactide were synthesized by polycondensation of PLLA diol ( = 10 000 g · mol?1), PCL diol ( = 10 000 g · mol?1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape‐memory properties. Random copolymers exhibited Rf and Rr values above 90% at 45 °C for an extremely large tensile strain of 1 000%.
The liquid‐crystalline side‐group polyacrylate PAC6 forms two mesophases in thin layers within the temperature range between 90 and 100 °C. The structures developing by self‐organization can be made clearly visible by Schlieren‐optical methods. If a low lateral temperature gradient is maintained in the temperature range mentioned above one can simultaneously and abreast observe four phases in PAC6 layers. Both new phases occur between the smectic and the nematic phase. Layer surface deformations arise during this phase transition. They were analyzed with a microscope interferometer. The PAC6 melt shows a considerable change of surface tension in this temperature range.
Schlieren‐optical image of a PAC6 layer with two mesophases. 相似文献
Crystalline‐branched supramolecular structures (CBSSs) with surface area (Brunauer‐Emmett‐Teller model) up to 350 m2 · g?1 were synthesized by in situ self‐assembly of the zigzag polyimide macromolecules under solvent‐thermal condition. The pore formation mechanism in these polyimides was supposed to be different from any microporous polymers ever reported. Although this family of porous polyimide does not belong to covalent organic frameworks (COFs), their high degree of crystallinity shows the possibilities that the dynamic covalent chemistry for synthesizing COFs could be extended from easily hydrolyzable B? O bond to a more stable imido bond. Therefore, we believe that these CBSSs could be useful in many applications, e.g., catalyst carriers and low‐K materials.
Poly(vinylsulfonic acid) (PVS) possesses a high acid content (ion‐exchange capacity in the chemical formula = 9.2 meq · g?1). Its monomer, vinylsulfonic acid (VSA), had a high acid dissociation ability (Hammett acid function = 0.74 in water), and a high ionic conductivity (0.04–0.11 S · cm?1). The radical polymerization of VSA with various initiators was kinetically investigated. The ESR spectrum of the VSA polymerization mixture showed a strong signal ascribed to the propagation carbon radical of VSA. The molecular weight of PVS increased with the increasing monomer concentration and decreasing radical initiator concentration to yield the PVS with a molecular weight of 4.0 × 104. Proton‐conductivity of PVS under hydrated and nonhumidified conditions was on the order of 10?1 and 10?3–10?6 S · cm?1, respectively.
Summary: Hydrophobically substituted diallylamines bearing a hexyl, dodecyl, or octadecyl chain were synthesized and homopolymerized as hydrochlorides. Copolymerization of the diallylamines with maleic acid produces alternating copolymers. The copolymers behave as amphiphilic polyampholytes and dissolve best in the acidic or in the basic form. Only the copolymer with the hexyl chain could be dissolved in aqueous solvents and shows hydrophobic association. The copolymers with the longer alkyl chains require polar protic organic solvents. All polymers are amorphous, but show a superstructure in bulk due to their amphiphilicity.
PEDOT is one of the most frequently studied conducting polymers in literature but values for optical transmission and electrical conductivity vary greatly. Therefore measurement protocols are examined and insights are suggested into why the protocols themselves may lead to differences. Reported PEDOT conductivity is the result of contact and non‐contact film thickness and four‐point probe measurements. The soft nature of PEDOT implies that any contact method must be executed with extreme care as values of conductivity ranging from 780 to 2 775 S · cm?1 can be obtained. Similarly, variations in the optical minimum, maximum, and transmission range are found based on different switching voltage protocols. The results present here highlight the need for explicitly stating the measurement protocol used.
Summary: In order to prepare well‐defined polymers on solid surfaces in the gas phase, a gas phase‐assisted surface polymerization (GASP) of vinyl monomers was carried out on solid surfaces pre‐coated with a photoiniferter, 2‐cyanoprop‐2‐yl N,N′‐dimethyldithiocarbamate, under UV irradiation. The GASP of methyl methacrylate (MMA) resulted in the formation of polymer on the surfaces and showed a proportional relationship between and polymer yield. Consecutive copolymerization of MMA and styrene led to the formation of a block copolymer, which was confirmed by a selective solvent fractionation method. These results demonstrate that controlled radical polymerization of vaporized monomer occurred on the solid surfaces.
Expected mechanism of GASP under UV irradiation. 相似文献
Fluorene‐based single‐chain copolymers with a white light emitter consisting of a blue and an orange chromophore have been synthesized and their photophysical and electroluminescent properties are investigated. The experimental results suggest that only a relatively small fraction of the orange‐emitting units incorporated into the fluorene is needed to achieve efficient white light emission by controlled incomplete energy transfer. A device from a copolymer with 0.02% DDQ content showed the highest external quantum efficiency of 2.64% with a luminance efficiency of 4.06 cd · A?1 with CIE coordinates (0.28, 0.24). The EL emissions are extremely stable over a wide range of current densities.
