Interfacial modification for controlling silica–polysiloxane interactions and bonding in some elastomeric composites

Silica reinforcing fillers were generated using the sol-gel approach and their surfaces were modified using either a vinyl alkoxysilane (to provide permanent bonding to a host poly(dimethylsiloxane) elastomer), or a hemiacetal ester (to provide bonding that could be thermally ruptured). The surface areas of the fillers were measured by nitrogen absorption, and their morphologies, interfacial structures, and crosslinking to the elastomer were characterized by ultra small angle and small angle X-ray scattering, scanning electron microcopy, and Fourier-transform infrared spectroscopy. Increasing the amount of the silane coupling agent decreased silica domain sizes, with corresponding increases in surface area and stronger filler-polymer interactions. Vinyltrimethoxysilane had a larger effect than vinylmethyldimethoxysilane. The tensile moduli, tensile strengths, and degrees of toughness of the composites were determined using stress-strain measurements in elongation, both under near-equilibrium conditions and under continuous extension. The permanently bonded modifications gave composites with improved mechanical properties. Rupturing the hemiacetal ester bonding at 120-150°C gave some increase in ultimate stress, maximum elongation, and toughness, thus underscoring the importance of interactions or 'networking' between filler particles.     

Development of an Exfoliated Nanocomposite Prepared by Vinyl Acetate and Organic Montmorillonite: Structure,Dynamic Mechanical Properties and Thermal Degradation

Using in-situ emulsion polymerization, the exfoliated nanocomposites were prepared from vinyl acetate (VAc) and organic montmorillonite (OMMT) through five different experimental conditions. The different experimental conditions and OMMT had little effect on the structure of PVAc–OMMT, but significant effect on the dynamic mechanical properties. They produced a combined effect on the modulus, loss tangent and glass transition temperature (T _g). OMMT could lower T _g of PVAc, and improved PVAc's low temperature resistance. PVAc and PVAc–OMMT all were homogeneous amorphous linear polymers and they all displayed cold crystallization. The different experimental conditions and OMMT had some effects on the thermal degradation. The thermal degradation process was found to consist of eight phases, and those of PVAc and PVAc–OMMT were similar. OMMT had no obvious effect on the thermal degradation temperature, but mainly delayed the thermal degradation process.     

Effect of Abrasives on Three-Body Abrasive Wear Behaviour of Particulate-Filled Polyamide66/Polypropylene Nanocomposites

Polyamide66/polypropylene (PA66/PP) blend, graphite (Gr)-filled PA66/PP composite and nanoclay (NC)-filled PA66/PP nanocomposites were prepared by twin screw extrusion and injection molding. Three-body abrasive wear behaviour of the injection moulded composites was carried out using a rubber wheel abrasion wear tester. In this study, angular silica sand and quartz particles of size ranging from 200 to 250 μm were used as dry and loose abrasives. The tests were carried out for 150, 300, 450 and 600 m abrading distances at a constant load of 36 N. It was observed that inclusion of particulate fillers in PA66/PP have significant influence on wear under varied abrading distances for different abrasive particles. Further, it was found that NC-filled PA66/PP nanocomposite exhibited lower wear rate compared to Gr filled ones for different abrasive particles. In addition, the worn surfaces of the samples were examined by scanning electron microscopy (SEM) and the morphology was also discussed.     

MOLECULAR ENGINEERING STUDIES ON NONTHROMBOGENIC BIOMATERIALS--A NOVEL CLASS OF NONTHROMBOGENIC BIOMATERIALS WITH ZWITTERIONIC STRUCTURE OF CARBOXYBETAINES

N,N-dimethyl-N-methacryloyloxyethyl-N-carboxyethyl ammonium (DMMCA) was graft-copolymerized onto the surface of segmented poly(ether urethane) (SPEU) and PE film. The carboxybetaine structure on SPEU and PE film surfaces was confirmed by ATR-FTIR, XPS and water contact angle measurements. Through the experiments with platelet adhesion and protein adhesion assay in vitro, the two materials studied, including poly-DMMCA gel, all show excellent nonthrombogenicity. This confirms once again that the zwitterionic molecular structure on the surfaces of materials is essential for improving their nonthrombogenicity and biocompatibility.     

STRUCTURE, MOLECULAR WEIGHT AND BIOACTIVITIES OF (1→3)-β-D- GLUCANS AND ITS SULFATED DERIVATIVES FROM FOUR KINDS OF LENTINUS EDODES

Lentinan samples, (1→3)-β-D-glucans containing 4.6-15.2 wt% proteins, coded as L-I1, L-I2, L-I3 and L-I4 (L-I)were isolated from four kinds of Lentinus edodes. These glucans were treated with acetone to remove the protein in order to obtain free protein glucans coded as LNP-I1, LNP-I2, LNP-I3 and LNP-I4 (LNP-I). The free-protein polysaccharides were sulfated to give derivatives (S-LNP-I) with degree of substitution (DS) from 0.4-0.8. The structural features and weight- average molecular weight (Mw) of the samples were investigated by using infrared spectroscopy, elemental analysis,13C-NMR, size exclusion chromatography combined with laser light scattering (SEC-LLS) and viscometry. The effects of structure and conformation of the polysaccharides on antitumor activities were assayed in vivo (Sarcoma 180 solid tumors)and in vitro (Sarcoma 180, HL-60, MCF-7 and Vero tumors). The results indicated that the predominant species of the samples L-I and LNP-I in 0.2 mol/L NaCl aqueous solution existed as triple-helical chains with high rigidity and in dimethyl sulfoxide (DMSO) as single-flexible chains. Interestingly, the antitumor activities of LNP-I are lower than those of the native glucans (L-I), whereas their sulfated derivatives have higher inhibition ratio against Sarcoma 180 than LNP-I. The results reveal that the binding of protein, sulfated modification and the triple helix conformation are important factors in the enhancement of the antitumor activities of polysaccharides on the whole.     

大环多胺的超分子识别作用

就大环多胺及配合物为主体分子对金属离子,磷酸根,氨基酸,肽及核苷酸等的超分子识别作用、影响因素和识别机制进行了简述。     

富勒烯的杯芳烃包合物的研究现状与展望

介绍了[60/70]富勒烯与杯[8],[6],[5]芳烃、高氧杂杯[3]芳烃及双杯芳烃形成包合物的研究进展和应用前景。     

计算烷烃沸点的新方法-基团键贡献法

根据分子中基团的特性和连接性,将基团贡献法和化学键贡献法结合在一起,发展了一种直接根据分子结构信息计算烷烃沸点的新方法-基团键贡献法,此方法同时具有基团贡献法和化学键贡献法的特点。对753种烷烃(C2～C100)的计算结果表明,沸点计算值与实验值的一致性令人满意,平均误差0.46%。     

新磺酰脲类除草活性构效关系的研究

磺酰脲类除草剂具有对环境友好和超高效的特点。本文采用X-衍射谱对其绝对构型进行分析,首次发现分子内氢键的存在。采用各种理论和软件计算,活性结构应符合三点要求：(a)分子内氢键使杂环和脲之间形成一个共轭体系;(b)羰基氧、磺酰氧和杂环氮形成分子中三个负电中心;(c)在磺酰胺与苯邻位取代基之间形成一个空穴。根据以上结论,构建了一个卡口模型,较合理地解释了磺酰脲类草活性的构效关系。建立了一个虚拟靶酶ALS的模拟作用模型,供进一步分子设计ALS抑制剂,包括一些非磺酰脲类先导化合物时参考。     

合成受体的分子识别

系统地总结了我们近年来在超分子化学研究中的一些工作进展,着重介绍了一些合成受体(环糊精,冠醚,杯芳烃)的分子识别和组装研究。