首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Summary: “True” initial polymerization rates can be calculated from the adiabatic temperature rise under isoperibolic conditions. They are much higher than initial polymerization rates measured by standard mass flow meter methods under quasi‐steady‐state conditions. These high initial rates are followed by a fast apparent deactivation (“attenuation”) until a constant (“plateau”) activity is reached at low polymerization yields of 2–3 g PP · (g catalyst)−1 caused by an “increasing degree of encapsulation” of active sites. Mass transfer limitations are not observed. Cross sectional SEM images of the polymer samples support these kinetic findings.

Rate of polymerization (g of PP · (g catalyst)−1 · h−1) and yield of polymerization (g of PP · (g catalyst)−1) as function of time.  相似文献   


2.
Summary: The synthesis of PEDOT nanoparticles and vesicles by dispersion polymerization in a methanol/water mixture (3/2, v/v) is reported, using either ammonium persulfate or iron(III) p‐toluenesulfonate as oxidants and α‐EDOT‐PEO as a reactive stabilizer. The influence of the oxidant as well as the α‐EDOT‐PEO molar mass and concentration on the core‐shell particle morphology and conductivity properties have been investigated. PEDOT particles with conductivities up to 1.5 × 10−2 S · cm−1 have been obtained in high yield.

TEM image of PEDOT vesicles prepared using PEO‐based stabilizers of 25 000 g · mol−1 in water/methanol mixture (2:3 v/v) at room temperature using ammonium persulfate as an oxidant.  相似文献   


3.
Summary: Alternating copolymers between substituted 1,3,5‐triazine (substituent = alkyl or amine) and thiophene or bithiophene are synthesized. The copolymer of amino‐1,3,5‐triazine with thiophene is soluble in organic solvents, transparent in most parts of the visible region, and photoluminescent. The copolymer receives electrochemical n‐doping with an Epc of −2.08 V vs Ag+/Ag and shows a time‐of‐flight electron drift mobility of 2.0 × 10−4 cm2 · V−1 · s−1, which is larger than that of widely used Al(8‐quinolinolato)3.

Structure of the poly(1,3,5‐triazine)s.  相似文献   


4.
Two novel spiro‐configured ter(arylene‐ethynylene) derivatives, TSF‐Cz and TSF‐F , have been designed and synthesized using spiro(fluorene‐9,9′‐xanthene) (SFX) as building blocks, introducing a hole‐transporting carbazole and a fluorene chromophore as the peripheral functional group into the backbone through an oxygen atom. The two well‐defined oligomers possess good solubility, film‐forming quality, and high Tg's at 140 and 126 °C, respectively. In addition, these oligomers exhibit blue photoluminescence (PL) emission both in solution and solid states. The double‐layered devices fabricated using the two materials as the emitter show a sky‐blue emission with a brightness and a current efficiency of 7 613 cd · m−2 and 1.11 cd · A−1 for TSF‐Cz , and 1 507 cd · m−2 and 0.36 cd · A−1 for TSF‐F , respectively.

  相似文献   


5.
Novel conjugated silole‐containing polyfluorenes, with green‐ and red‐emissive siloles on the backbone of the blue‐emissive polyfluorene are synthesized for white light electroluminescence (EL) from a single polymer with simultaneous red, green, and blue (RGB) emission. The CIE coordinates (0.33, 0.36) of the white light EL spectra are very close to that for pure white light (0.33, 0.33). The EL spectra are also quite stable at different applied voltages or brightness. The relative intensities for the three RGB peaks, at 450, 505, and 574 nm, were 0.94, 1, and 0.97, respectively, which demonstrates a balanced simultaneous RGB emission. A maximum luminous efficiency of 2.03 cd · A−1 for a brightness of 344 cd · m−2, and a luminous efficiency of 1.86 cd · A−1 for a more practical brightness of 2 703 cd · m−2, were achieved.

  相似文献   


6.
Chromophore‐containing dendritic structures (G1, G2) are utilized to intercalate layered silicates, which results in a large d‐spacing up to 126 Å. An exfoliated morphology is obtained by mixing the dendritic structure intercalated layered silicates with polyimide in N,N‐dimethylacetamide solution. The dendritic structures attached on the clay template would arrange in a non‐centrosymmetric manner. This self‐assembled arrangement brought about the electro‐optical coefficients of 5–6 pm · V−1 for these relatively low chromophore‐containing organic/inorganic nanocomposites without resorting to poling. Excellent temporal stability (100 °C) is also achieved.

  相似文献   


7.
A novel donor–acceptor‐type polymer with a low band‐gap that alternates electron‐rich thienylenevinylene groups with electron‐deficient diketopyrrolopyrrole (DPP) units (PETVTDPP) has been synthesized by Pd‐catalyzed Stille cross‐coupling polymerization. The polymer shows a broad absorption band of wavelengths that range from 330 to 900 nm, and a low band‐gap value of 1.43 eV. The field‐effect mobility of an organic thin‐film transistor based on this polymer is 0.05 cm2 · Vs−1. Bulk‐heterojunction solar cells using a mixture of PETVTDPP and PC[71]BM for the active layer show a power conversion efficiency (PCE) of 1.94% under simulated AM 1.5 G solar irradiation at 100 mW · cm−2.

  相似文献   


8.
Multiwalled carbon nanotube (MWCNT)‐coated polystyrene (PS) beads have been prepared by dispersion polymerization followed by a layer‐by‐layer self‐assembly method. The concentration of carboxylic acid groups on the MWCNTs increased from 1.81 × 1021 to 3.43 × 1022 COO per g as the treatment time was increased from 3 to 9 h. The sulfonated polystyrene (SPS) beads changed from being negatively charged to positively charged when the cationic polyelectrolyte was self‐assembled on their surface. The surface morphology of the adsorbed polyelectrolyte was smooth without any aggregation and the thickness of the polyelectrolyte coating on the SPS beads was ≈0.6 µm. The electrical conductivity and resistance of the MWCNT‐coated SPS beads were measured to be 4.0 × 10−2 S · cm−1 and 12.8 Ω at a volume fraction of 91%, respectively.

  相似文献   


9.
Porous polymeric monoliths were prepared via electron beam triggered free radical polymerization of (meth)acrylates. Post‐synthesis functionalization of these supports was accomplished via electron beam initiated free radical graft polymerization of methacryloyl‐substituted NHC precursors. The grafted precursors were converted into the corresponding copper complexes. Cu‐loadings were between 1.3 mg · g−1 and 1.5 mg · g−1. These supported catalysts were used in selected CO hydrosilylation and cyanosilylation reactions using a continuous flow setup.

  相似文献   


10.
PANI‐PAN coaxial nanofibers have been prepared by electro‐spinning during polymerization. The surface of the resulting nanofibers is superhydrophobic with a water contact angle up to 164.5°. Conductivity of the PANI‐PAN nanofibers is about 4.3 × 10−2 S · cm−1. The superhydrophobic nanofibers show a chemical dual‐responsive surface wettability, which can be easily triggered by changing pH value or redox properties of the solution. A reversible conversion between superhydrophobicity and superhydrophilicity can be performed in a short time. The strategy used here may provide an easy method to control the wettability of smart surfaces by using properties of low‐cost functional polymers.

  相似文献   


11.
Summary: An O‐hexyl‐3,5‐bis(terpyridine)phenol ligand has been synthesized and transformed into a hexagonal Zn(II)‐metallomacrocycle by a facile self‐assembly procedure capitalizing on terpyridine‐Zn(II)‐terpyridine connectivity. The structural composition was confirmed by NMR and mass spectral techniques; photo‐ and electroluminescence properties were also investigated. The OLED device shows green electroluminescent emission at 515 nm with a maximum luminance of 39 cd · m−2 and maximum efficiency of 0.16 cd · A−1.

Structure and electroluminescent properties of the metallomacrocycle investigated.  相似文献   


12.
Two multiblock copoly(arylene ether sulfone)s with similar block lengths and ion exchange capacities (IECs) were prepared by a coupling reaction between a non‐sulfonated precursor block and a highly sulfonated precursor block containing either fully disulfonated diarylsulfone or fully tetrasulfonated tetraaryldisulfone segments. The latter two precursor blocks were sulfonated via lithiation‐sulfination reactions whereby the sulfonic acid groups were exclusively placed in ortho positions to the many sulfone bridges, giving these blocks IECs of 4.1 and 4.6 meq·g−1, respectively. Copolymer membranes with IECs of 1.4 meq·g−1 displayed well‐connected hydrophilic nanophase domains and had decomposition temperatures at, or above, 300 °C under air. The copolymer with the tetrasulfonated tetraaryldisulfone segments showed a proton conductivity of 0.13 S·cm−1 at 80 °C under fully humidified conditions, and surpassed that of a perfluorosulfonic acid membrane (NRE212) by a factor of 5 at –20 °C over time.

  相似文献   


13.
The crossover from small‐molecule to polymer behavior in realistic models of PI at temperatures well above the glass transition is investigated by means of MD simulations. The molar masses range from the monomer to = 6 800 g · mol−1 which is far from the critical value for entanglement in PI. It is shown that at this temperature the non‐Gaussian parameter almost vanishes in the Q‐range studied. This implies Gaussian behavior in almost all the Q‐range. From the mean square displacement and the incoherent scattering function behavior a smooth transition from the microscopic regime to the Rouse dynamics is observed. The Rouse behavior is achieved at chain molecular weights of about 1 000 g · mol−1, which corresponds to 14 monomer units.

  相似文献   


14.
Greatly enhanced energy density in poly(vinylidene fluoride‐chlorotrifluoroethylene) [P(VDF‐CTFE)] is realized through interface effects induced by a photo cross‐linking method. Being different from nanocomposites with lowered dielectric strength, the cross‐linked P(VDF‐CTFE)s possess a high breakdown field as well as remarkably elevated polarization, both of which contribute to the enhanced energy density as high as 22.5 J · cm−3. Moreover, patterned thin films with various shapes and sizes are fabricated by photolithography, which sheds new light on the integration of PVDF‐based electroactive polymers into organic microelectronic devices such as flexible pyroelectric/piezoelectric sensor arrays or non‐volatile ferroelectric memory devices.

  相似文献   


15.
The electrical conductivity of composites of exfoliated graphite nanoplatelets (GNPs), including bromine‐doped GNP, and conjugated polyacrylonitrile has been investigated. The focal point is the dual nature of the graphite nanoparticles, which exhibit both intrinsic electrical conductivity and doping capability of semi‐conductive polymers such as conjugated polyacrylonitrile to form charge‐transfer complexes. The conductivity is particularly enhanced in conjugated polyacrylonitrile composites (e.g., with 6 wt.‐% graphite nanoplatelets) where the value rises from 1 × 10−10 to 2 × 10−3 S · cm−1, which reflects jointly the conductivity of the doped semi‐conductive polymer together with the percolation‐based conductivity of the particles.

  相似文献   


16.
Summary: The thiophene‐quinoxaline donor–acceptor conjugated copolymer poly[(thiophene‐2,5‐diyl‐alt‐(2,3‐diheptylquinoxaline‐5,8‐diyl)] (PTHQx) was explored as a semiconductor in thin‐film organic field‐effect transistors (OFETs). A hole mobility of 3.6 × 10−3 cm2 · V−1 · s−1 and an on/off current ratio of 6 × 105 were observed in p‐channel OFETs made from spin‐coated PTHQx thin films. The electronic structures of PTHQx and a related thiophene‐thienopyrazine donor–acceptor copolymer were calculated by density functional theory. Atomic force microscopy of PTHQx thin films showed a polycrystalline grain morphology that varied with the substrate.

Output (left) and transfer (right) characteristics of a PTHQx (structure shown) organic field‐effect transistor.  相似文献   


17.
Summary: A series of cross‐linked polythiophene derivatives ( P1 – 4 ) are synthesized by adding different ratio (0, 2, 5, and 10%) of conjugated cross‐linker via a Stille coupling reaction. From P1 – 4 , with the increase of the content of the conjugated bridges, the UV‐visible absorption peaks of the polymers were shifted towards blue and their electrochemical bandgap increased. The hole mobilities of P1 – 4 as determined from the SCLC model are 5.23 × 10−6, 1.28 × 10−4, 7.01 × 10−3, and 2.34 × 10−5 cm2 · V−1 · s−1, respectively. The PCEs of the polymer solar cells based on P1 – 4 are 0.37, 1.05, 1.26, and 0.78%, respectively. The improvement of PCE of the devices based on P2 – 4 compared with that of P1 may be due to the increase of hole mobility.

Molecular structure of the polythiophene derivatives ( P1 – 4 ).  相似文献   


18.
In the current contribution it is demonstrated – for the first time – that poly(ethylene) ( = 1 400 as well as 2 800 g · mol−1, PDI = 1.2) can be readily equipped with highly reactive cyclopentadienyl (Cp) end groups. The Cp terminal poly(ethylene) can subsequently be reacted in an efficient hetero Diels‐Alder (HDA) reaction with macromolecules (poly(isobornyl acrylate) ( = 4 600 g · mol−1, PDI = 1.10) and poly(styrene) ( = 6 300 g · mol−1, PDI = 1.13) featuring strongly electron withdrawing thiocarbonyl thio end groups, prepared via reversible addition fragmentation chain transfer (RAFT) polymerization employing benzylpyridin‐2‐yldithioformate (BPDF) as transfer agent. The resulting block copolymers have been analyzed via high‐temperature size exclusion chromatography (SEC) as well as nuclear magnetic resonance (NMR) spectroscopy. The current system allows for the removal of the excess of the non‐poly(ethylene) containing segment via filtration of the poly(ethylene)‐containing block copolymer. However, the reaction temperatures need to be judiciously selected. Characterization of the generated block copolymers at elevated temperatures can lead – depending on the block copolymer type – to the occurrence of retro Diels‐Alder processes. The present study thus demonstrates that RAFT‐HDA ligation can be effectively employed for the generation of block copolymers containing poly(ethylene) segments.

  相似文献   


19.
Summary: We report novel organic‐inorganic hybrid nanomaterials that consist of polymer hydrogel nanoparticles (nanogels) and calcium phosphate. Hybrid nanoparticles that measure ca. 40 nm are synthesized from a dilute solution of hydroxyapatite using nanogels as templates for calcium phosphate mineralization. These nanoparticles show a narrow size distribution and high colloidal stability. Nanogel‐adsorbed liposomes act as templates for hierarchical hybrid nanostructures. These nanohybrids can potentially be used as biocompatible drug carriers with controlled‐release properties.

TEM images of calcium phosphate nanoparticles formed in the presence of CHP nanogels (0.5 mg · mL−1) (left) and nanogel‐liposomes (CHP 0.05 mg · mL−1, DPPC 0.08 mg · mL−1)(right).  相似文献   


20.
We have studied the kinetics of polymeric nanoparticle formation for poly(styrene‐block‐4‐vinylpyridine) [P(S‐b‐4‐VPy)], chains in a non‐selective solvent using 1,4‐dibromobutane (DBB) as a cross‐linker by means of different nuclear magnetic resonance (NMR) spectroscopy techniques. The kinetic process was followed using 1H, 13C, and 2‐D Heteronuclear Single Quantum Correlation (HSQC) NMR experiments. The kinetic data obtained from 2‐D HSQC and 1H NMR experiments were in good agreement between them, proving the reliability of the 2‐D HSQC NMR technique for the in situ study of the kinetics of core‐shell nanoparticle formation. A value of 1.5 × 10−5 s−1 was determined for the apparent kinetic constant of the P(S‐b‐4‐VPy)‐DBB core‐shell nanoparticle formation process.

  相似文献   


设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号