Search

A new aromatic host polymer poly{[1,4-bis(9-decylcarbazole-3-yl)-2,3,5,6-tetrafluorobenzene-3,3-diyl]-alt-[N-methylisatin-2-one-3,3-diyl]} (PICzFB) containing carbazole-tetrafluorinebeneze-carbazole moiety in the -conjugated interrupted polymer backbone was synthesized by superacid-catalyzed metal-free polyhydroxyalkylation. The resulted copolymer PICzFB showed a comparatively wide band gap up to 3.32 eV and high triplet energy (E-T) of 2.73 eV due to confined conjugation by the C bond interrupted polymer backbone. Blue and green light-emitting devices with PICzFB as host, FIrpic and Ir(mppy)(3) as phosphorescent dopants showed the maximum luminous efficiencies of 5.0 and 27.6 cd/A, respectively. The results suggested that the strategy of incorporating bipolar unit into the -conjugated interrupted polymer backbone can be a promising approach to obtain host polymer with high triplet level for solution-processed blue and green phosphorescent polymer light-emitting diodes. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1037-1046

Phase transition and mobility of poly(N-isopropylacrylamide) (PNIPA) chains with three different types of end groups (hydroxyl, carbon-carbon double bond, and camphoric sulfonic groups) have been studied by measurements of the normal H-1 NMR spectrum, spin-spin relaxation time, and 2D NOESY spectrum. It is found that at room temperature not only the end group parts but also the part of the PNIPA chain with hydroxyl end group have higher mobility than corresponding parts of PNIPA with double bond and camphoric sulfonic end groups. The lower critical solution temperatures (LCST) of PNIPAs modified with hydrophilic hydroxyl and hydrophobic double bond end groups are inversely dependent and directly dependent on the molecular weight of polymer respectively, whereas the LCST of PNIPA with the camphoric sulfonic end group bearing both hydrophobic and hydrophilic structures is independent of the molecular weight. The double bond end groups collapse simultaneously with inner segments of the PNIPA chain, whereas the hydroxyl and camphoric sulfonic end groups still exhibit higher mobility and do not shrink tightly after heating-induced collapsing of inner segments. It is suggested that the hydroxyl and camphoric sulfonic end groups locate on the surface of globules, but the double bond end groups are probably buried inside the globules. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 749-755, 2011

Ethylene-(vinyl acetate) copolymer (EVA)/rectorite nanocomposites were prepared by direct melt extrusion of EVA and organo-rectorite. The microstructures and thermal properties of EVA nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), solid-state nuclear magnetic spectroscopy, positron annihilation spectroscopy, thermal gravimetric analysis (TGA) and dynamic mechanical analysis techniques. XRD pattern and SEM images show that the intercalated structure is formed and rectorite is finely dispersed in EVA matrix. When organoclay content of the hybrid increases to 7.5 wt%, or pristine rectorite was used instead of organoclay, the crystallization behavior of EVA nanocomposite changes greatly and the ratio of the monoclinic to orthorhombic crystal increases significantly. The relative fractional free volume of the nanocomposite decreases with the increasing organo-rectorite content, and the values of damping factor (tan delta) for all nanocomposites are lower than that of pure EVA. These facts illuminate that intercalated structure restricts the segment motion and mobilization of polymer chain. TGA results of EVA nanocomposites in air indicate that deacylation of EVA is accelerated because of the catalytic effect and the thermal degradation of the main chain is delayed owing to the barrier effect of silicate layers. (C) 2005 Society of Chemical Industry.

The effects of electron irradiation on the molecular chemical structure, conformation, mobility, and phase transition of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer have been investigated with variable-temperature, solid-state F-19 nuclear magnetic resonance (NMR). It has been found that electron irradiation converts all-trans conformations of both VDF-rich and TrFE-containing segments into dynamically mixed trans-gauche conformations accompanied by a simultaneous ferroelectric-to-paraelectric (or amorphous) transition. The variable-temperature F-19 magic-angle-spinning spectra results show that the paraelectric phase melts at much lower temperatures in irradiated films than in an unirradiated sample. Moreover, F-19 NMR relaxation data (spin-lattice relaxation times in both the laboratory and rotating frames) reveal that electron irradiation enhances the molecular motion in paraelectric regions, whereas the molecular motion in a high-temperature amorphous melt (> 100 degrees C) is more constrained in irradiated films. Besides these physical changes, electron irradiation also induces the formation of several CF3 groups. (c) 2006 Wiley Periodicals, Inc.

Solid-state nuclear magnetic resonance spectroscopy and relaxation measurements, together with DSC, have been used to elucidate the structures and molecular dynamics in poly(ethylene-co-vinyl acetate) (EVA). It has been found that besides immobile orthorhombic and monoclinic crystalline phases, the third mobile crystalline phase (possibly the phase) of a considerable amount (36% of total crystalline phases) appears in the EVA samples, which forms during room-temperature aging as a result of the secondary crystallization and melts at temperature somewhat higher than room temperature. Such a mobile crystalline phase has not only the well-defined chemical shift of its own, but also has different molecular mobility from the orthorhombic phase. The mobile crystalline phase is characterized by the rapid relaxation of the longitudinal magnetization, which is caused by conventional spin-lattice relaxation, while the slow relaxation of the longitudinal magnetization occurring in the orthorhombic phase is originated from the chain diffusion. In addition, the amorphous phase also contains two components: an interfacial amorphous phase and a melt-like amorphous phase. (c) 2006 Wiley Periodicals, Inc.

Hard carbon is one of the most promising anode materials for sodium-ion batteries, but the low Coulombic efficiency is still a key barrier. In this paper, a series of nanostructured hard carbon materials with controlled architectures is synthesized. Using a combination of in situ X-ray diffraction mapping, ex situ nuclear magnetic resonance (NMR), electron paramagnetic resonance, electrochemical techniques, and simulations, an “adsorption–intercalation” mechanism is established for Na ion storage. During the initial stages of Na insertion, Na ions adsorb on the defect sites of hard carbon with a wide adsorption energy distribution, producing a sloping voltage profile. In the second stage, Na ions intercalate into graphitic layers with suitable spacing to form NaC x compounds similar to the Li ion intercalation process in graphite, producing a flat low voltage plateau. The cation intercalation with a flat voltage plateau should be enhanced and the sloping region should be avoided. Guided by this knowledge, nonporous hard carbon material has been developed which has achieved high reversible capacity and Coulombic efficiency to fulfill practical application.

Na3Ni2SbO6 is prepared by solid state reaction of stoichiometric amounts of Na2CO3, Sb2O3, and NiO (900 °C, 12 h) as a cathode for Na-ion batteries.

In this work, the miscibility between chitin nanocrystals (ChNs) and poly(lactic acid) (PLA) was expected to be improved by surface acetylation of ChN. The reaction of acetic anhydride onto the ChN surface was confirmed by FTIR and C-13 NMR, while XRD and TEM proved the crystalline structure and rod-like morphology were maintained. The acetylated ChN (AChN) was incorporated into a PLA matrix by solution blending, and resulted in an increase of tensile strength and Young's modulus and they reached to the maximum value as 45 and 37% higher than neat PLA film, respectively, with the loading level of AChN reaching to 4 wt %. The enhancement could be attributed to that acetylation improved dispersion of AChN in the PLA matrix and interfacial adhesion between AChN and PLA. The performances of the nanocomposites based on PLA and chitin nanocrystals derived from renewable resources have good potential for industrial applications. (C) 2013 Wiley Periodicals, Inc.