The influence of nucleating agent on crystallization behavior and properties of polypropylene and its copolymer with ethylene

The influences of nucleating agent EDBS on crystallization behavior and properties of polypropylene UP) and its copolymer with a small amount (4. 48 %, molar fraction) of ethylene (CPP) were studied. DSC results indicated that the crystallization temperature of iPP and CPP samples with 0.5 % (mass fraction) EDBS obviously increased and the degree of crystallinity of these samples became higher. In addition, adding small amount of EDBS enhanced the crystallization of the low isotacticity and low molecular weight segments of the CPP. PLM results showed that their spherulite size decreased markedly, and as a result, the transmittance and haze of the films were all improved.

Non-isothermal crystallization behavior and kinetics of metallocene short chain branched polyethylene

The non-isothermal crystallization behavior and kinetics of metallocene short chain branched polyethylene were investigated via DSC at cooling rates from 2.5 to 20 degreesC/min, and subsequent heating at rate of 10 degreesC/min. To verify the effect of molecular weight and branching content on crystallization, three group samples were chosen: (1) linear polyethylene with low molecular weight and high molecular weight; (2) low molecular weight polyethylene with low branching content and high branching content; (3) high molecular weight polyethylene with low branching content and high branching content. The results show that crystallization temperature, crystallinity, melting temperature and crystallization rate are highly branching content-dependent. Molecular weight effect is less important, compared to branching content. A dramatic decrease of crystallization temperature, crystallinity, crystallization rate and melting temperature was observed for branched samples. The non-isothermal kinetics was analyzed via the methods, developed by Gupta and Mo Zhi-shen, and good agreement was obtained.

Oriented crystallization process of polypropylene fractions

Melting recrystallization processes of melt-sheared films of polypropylene (S28C) fractions have been investigated in situ by polarized optical microscope equipped with CCD camera and hot-stage. Actually, the morphological developments in the melting recrystallization are partially reappearance of oriented crystallization processes during melt-shearing the fractions, which is due to a memory effect of oriented structure of polymer. For low molecular weight fraction, only incomplete spherulites with some orientation along shear direction are observed in the melting recrystallization processes of the sheared films. For middle molecular weight fractions, extended chain fiber crystals(or bands) are formed first at higher temperatures, and the bands can act as self-nuclei (i. e., row nuclei), resulting in epitaxial growth of chain-folded lamellae(or fibril), i. e., the formation of cylindrites, with further decrease of the crystallization temperature. For high molecular weight fraction, however, it is not possible to shear the melt film because of its high melt viscosity. When the low molecular weight fraction in which no fiber crystals or cylindrites are observed, are mixed with small amount(about 1%-2%) of the high molecular weight fraction, quite large number of cylindrites are formed during the melting recrystallization process of its sheared film, which implies that the component of high molecular weight plays an important role in the formation of cylindrites during the shear process of polypropylene.

Effect of rare earth element on the metabolism in rats by high resolution proton nuclear magnetic resonance spectroscopy

The high-field nuclear magnetic resonance (NMR) spectra can be used for the rapid multicomponent analysis in small amounts of biological fluids. In this paper, the effect of La (NO3)(3) on the rats' metabolism in urine was investigated by H-1 NMR analysis. The experimental groups of wistar rats were injected intraperitoneally with La(NO3)(3) at doses of 0.2, 2.0, 10 and 20mg/kg body weight. The remarkable variation of low molecular weight metabolites in urine has been identified by H-1 NMR spectra, in which dimethylamine, N, N-dimethylglycine, urea, alpha -ketoglutarate, trimethylamine N-oxide, succinate, citrate and amino acids have been suggested as NMR markers for renal damage and ethanol, lactate, taurine as the markers for liver damage. This work may assess its possible use in the early detection of biochemical changes associated with Rare Earth induced kidney and liver dysfunction.

Monte Carlo simulation of pulsed-laser polymerization in emulsion

The pulsed-laser polymerization in emulsions has been simulated by the Monte Carlo method. Our simulation shows that the best measure of the propagation rate coefficients K-p is the peak maximum of molecular weight distribution for microemulsions when the droplets are small. However, the inflection point at the low-molecular-weight side of the peaks provides the best measure of K-p of bigger droplets. (C) 2000 Elsevier Science Ltd. All rights reserved.

Nuclear magnetic resonance studies on the effects of Rare Earth in rats urine

Male Wistar rats were administrated orally with La(NO3)(3) at doses of 0. 05, 0. 2, 2. 0, 10 and 20 mg/kg body weight. Urine was collected over a 24 h period after dosing. Resonances for a large number of low molecular weight metabolites were assigned in a high resolution H-1 NMR spectra of rat urine. The variation of some low molecular weight metabolites in urine provided a sensitive measurement of Rare Earth induced renal and liver lesions, in which DMA, DMG, urea, Kg, TMAO, succinate, citrate and amino acids have been suggested as NMR markers for renal damage and ethanol, lactate, taurine as the markers for liver damage. The method could be applicable to study of the toxicological effects of other compounds and drugs.

Studies on the structure and properties of thermotropic liquid crystalline poly(aryl ether ketone)s

Series of thermotropic liquid crystalline poly (aryl ether ketone) s were synthesized by mucleophilic substitution reactions of 4,4'-biphenol and substituted hydroquinone with different difluoromonomers, The relationship between structure and properties of the novel copolymers was investigated. For the copolymers with liquid crystalline properties, their melting transition temperatures show no great change with increase the content of the crystal-disrupting unit. The reason is that the crystal phase is directly transformed from the ordered liquid crystal phase. Side-groups have important effect on mesophase stability, The temperature range of mesophase stability for the chloro-polymers is smaller than those of other series of copolymers (P-phenyl, t-butyl, methoxy, 3-trifluoromethylbenzene). This behavior indicates that the effect of geometric repulsive factor on the thermodynamic stability of the mesophase is much larger than that of the polarizability attractive factor. Different ordered liquid crystal phases are observed in the polymers with different molecular weights. At low molecular weight, highly ordered smectic liquid crystal phases form. With increasing the molecular weight, the ordered degree of the liquid crystals decreases, and only the nematic liquid crystal phase is observed in the polymer with higher molecular weight.

Preparation and characterization of polymer-supported rare earth complexes

The polymers containing different ligand groups of atoms (mainly O, N, and S) and their rare earth complexes were prepared, characterized and classified based on the type of metal-ligand tending. The catalytic activities of the complexes are briefly discussed. The polymer-supported rare earth complexes showed much greater activities than the corresponding complexes with a low molecular weight.

SYNTHESIS AND CHARACTERIZATION OF POTENTIALLY BIODEGRADABLE THERMOTROPIC POLYESTERS BASED ON P-HYDROXYBENZOIC ACID AND GLYCOLIC ACID

The synthesis of novel thermotropic liquid crystalline copolyesters derived from aliphatic hydroxy acid (glycolic acid, GA) and aromatic hydroxy acid (p-hydroxybenzoic acid, PHBA) via a melt-copolycondensation process in the presence of various catalysts

SYNTHESIS AND CHARACTERIZATION OF POLYMER-SUPPORTED LANTHANIDE COMPLEXES AND BUTADIENE POLYMERIZATION BASED ON THEM

Poly(styrene-acrylic acid)-lanthanide (Ln.PSAA) and poly(ethylene-acrylic acid)-neodymium (NdPEAA) complexes have been prepared and characterized. The infrared and X-ray photoelectron spectra indicate that the lanthanide complexes possess the bidentate carboxylate structure Ln-O-C(R)-O (see structure B in text). The catalytic behavior of the complexes has been described. The catalytic activities of Nd.PSAA and Nd.PEAA are much greater than that of the corresponding low molecular weight catalyst for butadiene polymerization. The activities of various individual lanthanide elements are quite different from one another. Neodymium shows the highest activity. Europium, samarium and the heavy elements exhibit very low or no activities. The cis-1,4 content of the polybutadiene obtained is not affected by different lanthanide elements in the series. The complex with the intermediate content of the functional group has a higher activity than the others. The polymer-supported lanthanide complexes having different constitutions have different catalytic activities. When the molar ratio of lanthanide to the functional group is ca. 0.2, the activity of the complex is in the optimum state. The activity is influenced by the dispersion of the lanthanide metal immobilized on the polymer chain. Catalytic activity can be improved by adding other metals to the catalyst system.

SYNTHESIS AND PROPELLER-PROPELLER TRANSITION OF OPTICALLY-ACTIVE POLY(DIPHENYL-O-TOLYLMETHYL METHACRYLATE)

Diphenyl-o-tolylmethyl methacrylate (DPTMA) was synthesized and polymerized using initiators of organolithium complexes with (+) - (2S,3S) -dimethoxy-1,4-bis(dimethylamino) butane (DDB) and (-) -sparteine (Sp) as the chiral ligands. DDB was suitable for its complex effective to prepare optically active poly(diphenyl-o-tolylmethyl methacrylate) (PDPTMA) with one-handed helical conformation, whereas only low-molecular weight polymer was formed when Sp was used as ligand due to the repulsive hindrance between the triarylmethyl group and the ligand. A new mutarotation, propeller-propeller transition, was observed for PDPTMA from the optical rotation curves and CD spectra in THF solution. The equivalent period of PDPTMA was estimated to be 14 angstrom based on the x-ray diffraction. (C) 1993 John Wiley & Sons, Inc.

THERMODYNAMICS OF POLY(ETHYLENE OXIDE)-POLY(VINYL ACETATE) BLENDS

Heat-of-mixing data, obtained on blends of poly(ethylene oxide) (PEO) with whole and fractionated poly(vinyl acetate) (PVAc), were used to feed Patterson's theory of polymer-polymer miscibility. Negative values of mixing enthalpy, contact-energy term, interaction'' parameter and excess volume were obtained only for blends with the lowest molecular weight PVAc fraction. These results show that miscibility of PVAc with PEO strongly depends on its molecular weight. The calculated unfavourable excess volume term of the Patterson equation is small in comparison with the absolute value of the interaction term. Therefore, miscibility of PEO and low-molecular-weight PVAc is dictated by the weak specific interactions between different repeat units and by the entropic gain in the mixing process.

Preparation of 1,3,5-thiadiazine-2-thione derivatives of chitosan and their potential antioxidant activity in vitro

Three new kinds of 1,3,5-thiadiazine-2-thi one derivatives of chitosan with two different molecular weight (SATTCS1, SATTCS2, TITTCS1, TITTCS2, CITTCS1 and CITTCS2) have been prepared. Their structures were characterized by IR spectroscopy. The substitution degree of derivatives calculated by elemental analyses was 0.47, 0.42, 0.41, 0.38, 0.41 and 0.36, respectively. The result shows that substitution degree of derivatives was higher with lower molecular weight. The antioxidant activity was studied using an established system, such as bydroxyl radical scavenging, superoxide radical scavenging and reducing power. Antioxidant activity of the 1,3,5-thiadiazine-2-thione derivatives of chitosan were stronger than that of chitosans and antioxiclant activity of low molecular weight derivatives were stronger than that of high molecular weight derivatives. It is a potential antioxidant in vitro. (c) 2007 Elsevier Ltd. All rights reserved.

Structural studies on a novel fucogalactan sulfate extracted from the brown seaweed Laminaria japonica

A low molecular weight fucogalactan, obtained from the brown seaweed Laminaria japonica, was separated into three fractions (LF1, LF2 and LF3) by DEAE-Sepharose FF column chromatography. All three fractions contained predominantly fucose, sulfate group and galactose. The results showed that the main fraction LF2 consisted of L-fucose, D-galactose and sulfate at a molar ratio 6:1:9. Structural study on the LF2 was carried out by NMR spectroscopy. The backbone of LF2 was primarily (1 -> 3)-linked alpha-L-fucopyranose residues (75%) and a few (1 -> 4)-alpha-L-fucopyranose linkages (25%). The branch points were at C-4 of 3-linked alpha-L-fucopyranose residues by beta-D-galactopyranose unites (35%, molar ratio) or at C-2 of 3-linked alpha-L-fucopyranose residues by non-reducing terminal fucose unites (65%, molar ratio). Sulfate groups occupied at position C-4 or C-2, sometimes C-2, 4 to fucose residues, and C-3 and/or C-4 to galactose residues. The structure of LF2 was supposed as following: [GRAPHICS] (C) 2010 Elsevier B.V. All rights reserved.

天山乌鲁木齐河源1号冰川成冰过程的地球化学研究--以低分子有机酸为主

冰川上的表面雪层是联系大气成分与冰芯记录的重要纽带，对雪－冰现代过程的研究将有助于正确解释保存在冰芯中的古气候和环境信息。山地冰川雪冰中有机酸记录的研究在认识有机酸生物地球化学循环方面占很大的优势，本文依托天山冰川观测试验站开展的冰雪物理、化学现代过程方面的研究，对乌鲁木齐河源1号冰川中低分子有机酸和无机阴离子在成冰作用过程中的迁移转化进行了研究。新雪和保存较好的表层雪主要用来分析采样点低分子有机酸和无机阴离子的季节变化特征，粒雪坑样品主要用于进行低分子有机酸和无机阴离子沉积后过程的研究。 雪冰样品采集于1号冰川东支东经86°49′，北纬43°06′，海拔4 130 m 处，2004年3月至2005年3月期间，共获取了23个连续雪坑剖面的粒雪样品。采用美国Dionex公司的ICS-90型离子色谱仪加RFC-30型淋洗液在线发生器进行测定，检测到的低分子有机酸主要有HCOO-、CH3COO-、C2H5COO- 和(COO)22-，无机阴离子主要有F-、Cl-、NO2-、NO3-、SO42- 和PO43-。 表层雪是研究粒雪化和成冰作用过程中化学组成变化的起点。为配合天山乌鲁木齐河源1号冰川沉积后过程中化学组成变化的研究，我们首先对表层雪样品（雪坑表层5cm的雪样）进行了低分子有机酸和无机阴离子含量的分析。结果显示，除(COO)22- 外，大部分有机酸和高浓度的无机阴离子因受到周围环境和盛行风的影响呈现出明显的季节变化特征，即夏半年离子浓度变化剧烈，最大值和最小值同时出现在夏半年，冬半年的浓度则相对小而稳定；而(COO)22- 和低浓度的无机阴离子随季节变化的特征不明显，在全年均显示出波动性。数据表明，在外界条件不变的情况下，表层雪可以长时间（至少半年时间）保存其中高含量的化学组成不被改变。 通过对高含量低分子有机酸和高含量无机阴离子的沉积后过程的研究，发现它们在沉积后的迁移转化过程受温度和融水的影响较大，在不同时期表现出不同的季节变化特征。雪层消融初期，淋溶作用导致雪层内的大部分离子组分进入初始融水中，并随着融水下渗、聚集，使下部雪层中离子组分的浓度不断增加；当消融进一步加剧，大部分低分子有机酸和无机阴离子随融水径流而流失，雪层中记录的低分子有机酸和无机阴离子含量迅速降低；在消融季节，峰值向雪坑底部移动的速度较快。在冬半年的负温条件下，雪层中记录的低分子有机酸和无机阴离子的含量及其保存在雪坑下部的峰值都相对稳定，这也再次说明如果外界条件不发生改变，雪冰可以长时间（至少半年时间）保存其中的化学组成不被改变这个结论；另外，冬半年雪坑上部记录的峰值在一定程度上可以反映它们在大气中的初始水平。CH3COO- 和(COO)22- 的峰值通常会出现在污化层的附近，与污化层的位置具有较好的一致性，说明污化层对CH3COO- 和(COO)22- 的沉积后过程可能有一定的影响。