Improved thermal fractionation technique for chain structure analysis of ethylene/alpha-olefin copolymers

In this report, we describe an improved thermal fractionation technique used to characterize the polydispersity of crystalline ethylene sequence length (CESL) of ethylene/alpha -olefin copolymers. After stepwise isothermal crystallization, the crystalline ethylene sequences are sorted into groups by their lengths. The CESLs are estimated using melting points of known hydrocarbons. The content of each group is determined using the calibrated peak area. The statistical terms: the arithmetic mean (L) over bar (n), the weighted mean (L) over bar (w) and the broadness index I = (L) over bar (w)/(L) over bar (n) are used to describe the distribution of CESL. Results show that improved thermal fractionation technique can quantitatively characterize the polydispersity of CESL with a high degree of accuracy.

稀土及其配合物对蛇毒磷脂酶A_2活性的影响

分别研究了三价稀土离子 (La3 + ,Eu3 + ,Dy3 + ,Yb3 + )、二乙三胺五乙酸及其衍生物二乙三胺五乙酸 -双二甲酰胺 ,二乙三胺五乙酸 -双 (异烟肼 )与稀土离子的配合物以及Tb -谷氨酰胺配合物对蛇毒磷脂酶A2 活性的影响 .浓度低于 <3μmol/L的稀土离子可以激活磷脂酶A2 ,浓度大于 5 μmol/L后稀土离子对酶活性表现出抑制作用 ;外源Ca2 + 离子的加入可以缓解稀土离子对酶活性的抑制作用 ,表明稀土离子和钙离子是竞争性地结合在酶的活性部位 ;稀土离子和二乙三胺五乙酸及其衍生物的配合物对酶活性没有明显影响 ;Tb -谷氨酰胺在浓度大于 10 μmol/L后开始抑制酶的活性

Structural phase transition in the layered perovskite compound BaTb2Mn2O7

A distorted layered perovskite compound BaTb2Mn2O7 was synthesized by the solid state reaction in pure argon. There is a structural phase transition in the BaTb2Mn2O7 compound. The phase transition was characterized by the DSC and high temperature Xray diffraction. The heat capacity of BaTb2Mn2O7 was calculated. The thermal anomaly corresponding to the phase transition was observed at about 740K. The lattice parameters were calculated by the CELL program for BaTb2Mn2O7, It has Tb-type orthorhombic symmetry with a = 0.3908 nm, b = 0.3866 nm, c = 2.0163 nm, and space group Immm at room temperature. With the increase of temperature, the lattice parameters gradually increase until 673K. From 723K to 973K, the compound translates to tetragonal with a = 0.39078 nm, c = 2.0277 nm and S.G. I4/mmm. This result is fairly in accordance with that of heat capacity.

Observation of inverted phases in poly(styrene-b-butadiene-b-styrene) triblock copolymer by solvent-induced order-disorder phase transition

We report observation of inverted phases consisting of spheres and/or cylinders of the majority fraction block in a poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer by solvent-induced order-disorder phase transition (ODT). The SBS sample has a molecular weight of 140K Da and a polystyrene (PS) weight fraction of 30%. Tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM) were utilized to study the copolymer microstructure of a set of solution-cast SBS films dried with different solvent evaporation rates, R. The control with different R leads to kinetic frozen-in of microstructures corresponding to a different combination parameter chi (eff)Z of the drying films (where chi (eff) is the effective interaction parameter of the polymer solution in the cast film and Z the number of "blobs" of size equal to the correlation length one block copolymer chain contains), for which faster evaporation rates result in microstructures of smaller chi (eff)Z. As R was decreased from rapid evaporations (similar to0.1 mL/h), the microstructure evolved from a totally disordered one sequentially to inverted phases consisting of spheres and then cylinders of polybutadiene (PB) in a PS matrix and finally reached the equilibrium phase, namely cylinders of PS in a PB matrix. We interpret the formation of inverted phases as due to the increased relative importance of entropy as chi (eff)Z is decreased, which may dominate the energy penalty for having a bigger interfacial area between the immiscible blocks in the inverted phases.

Synthesis, structure and ring-opening polymerization of phenolphthalein macrocyclic polyarylates

Phenolphthalein based polyarylate macrocyclic oligomers were selectively synthesized by an interfacial polycondensation reaction of o-phthaloyl dichloride with phenolphthalein. The high selectivity benefits from the role of phenolphthalein as a color indicator, an efficient phase transfer catalyst, acid a preferred conformation of the starting materials as indicated by analyzing a single-crystal X-ray structure of an analogous macrocycle. The melt ROP of phenolphthalein polyarylate cyclic dimer was studied using nucleophilic initiators, The molecular weight of the resulting polymers builds up very rapidly at the very early stage of polymerization but decreases with time. During the ROP of cyclic dimer, analogous macrocycles with higher degree of polymerization (n greater than or equal to 3) and linear oligomers were produced by backbiting reaction especially at later stage of polymerization. Conversion of cyclic dimer is very fast at the earlier stage of polymerization and then increases slowly with time as analyzed by gel permeation chromatography. However, the total amount of cyclic oligomers in the ROP system increases with time at the later stage of polymerization because of the formation of larger macrocycles. The resulting polymers are amorphous. Glass transition temperatures (T(g)s) of these polymers are influenced by the polymerization time, type of initiator, and initiator concentration.

Novel trichromatic phosphor codoped with two rare earth ions in a single matrix

The luminescence properties of CaBPO5: Eu, Tb phosphor and the sensitization of Ce3+ were investigated. The CaBPO5: Eu, Tb phosphors were synthesized in the ambient air and the emission spectra of Eu3+, Tb3+ and Eu2+ were Observed in the phosphor. The result shows that there is electron transfer between conjugate rare earth ions. Sensitization of Ce3+ can improve the intensity of emission of Tb3+ and Eu2+. A novel trichromatic lamp phosphor codoped with Eu3+-Tb3+ in matrix CaBPO5 is then predicted.

Crystallization kinetics of narrow molecular weight distribution metallocene short-chain-branched polyethylene

Isothermal and non-isothermal crystallization kinetics of three metallocene-catalysed short-chain-branched polyethylene (SCBPE) fractions with different degree of branching were investigated by using differential scanning calorimetry (DSC). Narrow molecular weight fractions (M-w = 20,000 and M-w/M-n < 1.15) are used and the degree of branching (CH3 per 1000C) are 1.6, 10.4, 40 respectively. The regime I - II transition temperature are 119.8C, 115.9 degreesC, 113.3 degreesC with the decreasing of degree of branching. Increasing the branch content decreases the rate of secondary nucleation, i,relative to the rate of surface spreading and so increases the range of supercooling over which regime I exists. The rate of bulk crystallization for both isothermal and non-isothermal crystallization decreases with the increasing of degree of branching. Both Ozawa Equation and Kissinger Equation are invalid for non-isothermal crystallization kinetics of SCBPE fractions,that means the effects of the branched chain on crystallization process are more complex than expected.

Preparation, characterization and photophysical properties of layered zirconium bis(monohydrogenphosphate) intercalated with rare earth complexes

Two kinds of rare earth (RE) complexes were intercalated into zirconium bis(monohydrogenphosphate) (alpha -ZrP) by exchanging the RE complexes into the p-methyoxyaniline (PMA) preintercalated compound Zr(O3POH)(2). 2PMA (alpha -ZrP . 2PMA). Powder X-ray diffraction patterns reveal that Eu(DBM)(3)phen (DBM: dibenzoylmethane, phen: 1,10-phenanthroline) and Tb(AA)(3)phen (AA: acetylacetone) intercalated into alpha -ZrP . 2PMA. This was confirmed by the UV-visible spectra of both the RE complexes and the assemblies. At the same time, the assemblies have better luminescent properties, and the fluorescent lifetimes of RE3+ in the excited state in the assemblies are much longer than those in the complexes. The stabilities of the assemblies under UV radiation are much better than those of the RE complexes.

Investigating mechanical response of single chain polystyrene particles by scanning probe techniques

Single chain polystyrene particles were obtained by dilute solution casting method. The sample with both single chain polystyrene particles and multi-chain (more than 1000 molecular chains) polystyrene particles was obtained by a little more concentrate solution. Force modulation technique showed that single chain polystyrene particles were softer than multichain polystyrene particles. On the other hand, nanoindentation experiments on multi-chain particles and bulk polystyrene manifested that the elastic modulus of multi-chain polystyrene particles was very close to that of bulk polystyrene. Therefore, it was concluded that single chain polystyrene particles were softer than bulk polystyrene,which indicated that the density of intrachain entanglement points in the single chain polystyrene particles was not as large as that of the interchain entanglement points in the bulk state.

Nanostructure and mechanical measurement of highly oriented lamellae of melt-drawn HDPE by scanning probe microscopy

Scanning probe microscopy was used to simultaneously determine the molecular chain structure and intrinsic mechanical properties, including anisotropic elastic modulus and friction, for lamellae of highly oriented high-density polyethylene (HDPE) obtained by the melt-drawn method. The molecular-scale image of the highly oriented lamellae by friction force microscopy (FFM) clearly shows that the molecular chains are aligned parallel to the drawing direction, and the periodicities along and perpendicular to the drawing direction are 0.26 and 0.50 nm, respectively. The results indicate that the exposed planes of the lamellae resulting from the melt-drawn method are (200), which is consistent with results of transmission electron microscopy and electron diffraction. Because of the high degree of anisotropy in the sample, coming from alignment of the molecular chains along the drawing direction, the measured friction force, F, determined by FFM is strongly dependent on the angle, theta, between the scanning direction and the chain axis. The force increases as theta is increased from 0 degrees (i.e., parallel to the chain axis) to 90 degrees (i.e., perpendicular to the chain axis). The structural anisotropy was also found to strongly influence the measurements of the transverse chain modulus of the polymer by the nanoindentation technique. The measured value of 13.8 GPa with transverse modulus was larger than the value 4.3 GPa determined by wide-angle X-ray diffraction, which we attributed to anisotropic deformation of the lamellae during nanoindentation measurements that was not accounted for by the elastic treatment we adopted from Oliver and Pharr. The present approach using scanning probe microscopy has the advantage that direct correlations between the nanostructure, nanotribology, and nanomechanical properties of oriented samples can be determined simultaneously and simply.

Degradation of polyimide induced by nitrogen laser irradiation

The degradation behavior of polyimide (PMDA-ODA) induced by nitrogen laser irradiation was studied. The changes in the surface morphology and the composition of the irradiated polyimide films were examined by scanning electron microscopy, X-ray photoelectron spectroscopy and FT-IR spectroscopy. The initial reaction was achieved by photochemical degradation of polyimide in the highly electronic excited state by the absorption of a second 337 nm photon. Atmospheric oxygen sequentially reacted with the produced radicals to form a highly oxidized layer. The formation of carbonyl group was enhanced by the heat remaining on the irradiated polyimide film surfaces. (C) 2000 Elsevier Science B.V. All rights reserved.

Excimer-laser irradiated polyimide films as temperature-sensitive materials

The temperature dependence of the resistivity of KrF laser irradiated polyimide films was studied. In all cases, the resistivity decreased with increasing temperature. The irradiated polyimide film exhibited a typical semiconducting property. This result indicated that the irradiated polyimide films can be used as temperature-sensitive materials. We demonstrated that both the sensitivity and the sensitive temperature range of the irradiated polyimide films can be altered by adjusting laser irradiation parameters. The intrinsic relationship between the temperature coefficient of the resistivity and irradiation condition was interpreted in terms of the microstructural change. The result provided a new insight into the fundamental aspects of laser irradiated polyimide film structure and a method of preparing temperature-sensitive materials. (C) 2000 Elsevier Science B.V. All rights reserved.

Luminescent properties of organic-inorganic hybrid monoliths containing rare-earth complexes

Transparent organic-inorganic hybrid monoliths containing rare-earth complexes (Eu(TTA)(3)Phen, Tb(Sal)(3)) were prepared via the sol-gel technique. It could be observed by transmission electron microscopy that the fluorescent particles are distributed in the matrix at the microscopic level. The matrix is composed of organic-inorganic semiinterpenetrating networks, i.e., PHEMA-SiO2 system. The fluorescence emission spectra of samples are similar to those from corresponding powdered Eu(III) and Tb(III) complexes, and the half-widths of the strongest bands are less than 10 nm, which indicates that the monolith exhibits high fluorescence intensity and color purity. Furthermore, the fluorescence spectra exhibit no obvious change with decreasing nanoparticle size of the rare-earth complex. The fluorescence lifetimes of samples are longer than pure Eu(III), Tb(III) complexes, respectively. Samples irradiated with an UV lamp (365 nm) are still transparent but become bright red and green in color due to fluorescence of Eu(III) and Tb(III) complexes. (C) 2000 Elsevier Science B.V. All rights reserved.

Synthesis and electroluminescent properties of a novel terbium complex

A new carboxylic acid ligand (o-amino-4-hexadecane benzoic acid, AHBA) and a corresponding terbium complex (Tb(AHB)(3)) were synthesized and characterized. A multilayer electroluminescent device with poly(N-vinylcarbazole) (PVK), 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) and the terbium complex as emissive layer was fabricated: glass substrate/ITO/PPV/PVK:-To(AHB)(3):PBD/Alq(3)/Al. The photoluminescence (PL) and electroluminescence (EL) spectra were discussed. This EL cell exhibited characteristic emission of terbium ions with a maximum luminance of 35 cd/m(2) at 20 V. (C) 2000 Elsevier Science S.A. All rights reserved.

Green electroluminescence generated from the thin film based on a soluble lanthanide complex

Electroluminescent (EL) devices based on a soluble complex Tb(MDP)(3) [Tris-(monododecyl phthalate)Terbium] doped with poly (N-vinylcarbazole) (PVK), (2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole) (PBD) were fabricated. The device structures of ITO/PVK/PVK:PBD:Tb(MDp)(2)/Aiq(3)/Al and ITO/PVK:PBD:Tb(MDP)(3)/Alq(3)/Al were employed. The Tb(MDP), as emissive layer was spin-coated. The EL cell exhibited characteristic emission of terbium ion. (C) 2000 Elsevier Science S.A. All rights reserved.