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Various Polymers (various + polymer)
Selected AbstractsTuning the Refractive Index of Polymers for Polymer Waveguides Using Nanoscaled Ceramics or Organic Dyes,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2004J. Böhm Plastic Optical Fibers (POF) show advantageous properties like high flexibility and their cost advantage in comparison to glass fibers. The refractive indices of core and cladding have to be modified in order to get total reflectance. Thus, there is a strong demand for refractive index adjustable polymers with improved transmission properties in the visible and the NIR range. Inorganic nanosized particles or organic dyes homogeniously dispersed or solved in the polymer matrix allow a tailored increase or decrease of the refractive index of various polymers. [source] Multicolor Fluorescent and Permeation-Selective Microbeads Enable Simultaneous Sensing of pH, Oxygen, and TemperatureADVANCED MATERIALS, Issue 21 2009Matthias I. J. Stich Multicolor fluorescent microbeads made from various polymers and incorporated into a binder polymer to produce a material whose three signals (measuring pH, temperature, and presence of O2) can be unambiguously assigned after either spectral or time-resolved separation. This renders the material well suited for continuous sensing of these parameters in blood or other bioliquids. [source] Carbon Nanosheets for Polymeric Nanocomposites with High Thermal ConductivityADVANCED MATERIALS, Issue 20 2009L. Monica Veca Nanometer-thick 2D carbon structures ("carbon nanosheets") are processed from commercially available expanded graphite. These carbon nanosheets are then incorporated in various polymers to produce flexible nanocomposites that exhibit record-setting anisotropic thermal conductivities, which may prove highly valuable in many technological applications. [source] Palladium-Catalyzed Oxidation of Phenyl-Substituted Alkenes using Molecular Oxygen as the Sole OxidantADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Aline Abstract The palladium-catalyzed aerobic oxidation of styrene and 2-vinylnaphthalene in dimethylacetamide/water or dimethylformamide/water solutions under mild conditions has been developed, in which palladium(II) chloride is used in the absence of co-catalysts or special stabilizing ligands as the sole and recyclable catalyst. The corresponding methyl ketones have been obtained in good to excellent yields with low catalyst loadings (0.2,5,mol%) and high turnover numbers (up to ca. 1000 to palladium). This simple and efficient catalytic method represents an ecologically benign and economically attractive synthetic pathway to industrially important compounds used in the manufacture of various polymers and drugs. [source] Novel polymeric flocculants based on polyacrylamide grafted dextran in kaolin suspensionJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010S. Krishnamoorthi Abstract A study is done on ceric-ammonium-nitrate (CAN) initiated graft copolymerization of polyacrylamide (PAM) on to dextran (Dx) by solution polymerization technique. The average molecular weight of dextran is 7.0 × 10,6 g/mole. By changing the concentrations of the initiator in the reaction feed, a series of graft copolymer (Dx-g-PAM1 to Dx-g-PAM4) with variation in the number and length of the grafted PAM chains are obtained. The flocculation characteristics of various polymers are investigated by the use of settling tests in 2 wt % using kaolin suspensions. Among the series of graft copolymers, the one with highest molecular weight shows superior performance. The flocculation characteristics of the best-performing graft copolymer (Dx-g-PAM3) are compared with those of various commercially available flocculants and PAM in the kaolin suspension. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] An In Vivo Study of the Host Response to Starch-Based Polymers and Composites Subcutaneously Implanted in RatsMACROMOLECULAR BIOSCIENCE, Issue 8 2005Alexandra P. Marques Abstract Summary: Implant failure is one of the major concerns in the biomaterials field. Several factors have been related to the fail but in general these biomaterials do not exhibit comparable physical, chemical or biological properties to natural tissues and ultimately, these devices can lead to chronic inflammation and foreign-body reactions. Starch-based biodegradable materials and composites have shown promising properties for a wide range of biomedical applications as well as a reduced capacity to elicit a strong reaction from immune system cells in vitro. In this work, blends of corn starch with ethylene vinyl alcohol (SEVA-C), cellulose acetate (SCA) and polycaprolactone (SPCL), as well as hydroxyapatite (HA) reinforced starch-based composites, were investigated in vivo. The aim of the work was to assess the host response evoked for starch-based biomaterials, identifying the presence of key cell types. The tissues surrounding the implant were harvested together with the material and processed histologically for evaluation using immunohistochemistry. At implant retrieval there was no cellular exudate around the implants and no macroscopic signs of an inflammatory reaction in any of the animals. The histological analysis of the sectioned interface tissue after immunohistochemical staining using ED1, ED2, CD54, MHC class II and ,/, antibodies showed positively stained cells for all antibodies, except for ,/, for all the implantation periods, where it was different for the various polymers and for the period of implantation. SPCL and SCA composites were the materials that stimulated the greatest cellular tissue responses, but generally biodegradable starch-based materials did not induce a severe reaction for the studied implantation times, which contrasts with other types of degradable polymeric biomaterials. [source] Hysteretic magnetoresistance in polymeric diodesPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7-8 2009Sayani Majumdar Abstract We report on hysteretic organic magnetoresistance (OMAR) in polymeric diodes. We found that magnitude and lineshape of OMAR depend strongly on the scan speed of the magnetic field and on the time delay between two successive measurements. The time-dependent OMAR phenomenon is universal for diodes made with various polymers. However, the width and magnitude of OMAR varied with the polymeric material. The suggestive reason for this hysteretic behavior is trapped carriers, which in presence of a magnetic field change the ferromagnetic ground-state of the polymer leading to a long spin relaxation time. These experimental observations are significant for clarification of the OMAR phenomenon. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation and characterization of polyurethane,gold nanocomposites prepared using encapsulated gold nanoparticlesPOLYMER INTERNATIONAL, Issue 7 2010Chao-Ching Chang Abstract Gold nanoparticles (GNPs) have been widely studied due to their unique properties. Although many research groups have developed the synthesis of GNPs using various polymers as stabilizing or reducing agents, the effects of GNPs on the structures and properties of polymer matrices have been less reported. We propose a new design for the preparation of polyurethane,gold (PU,Au) nanocomposites. 11-Mercapto-1-undecanol-coated GNPs acted as the chain extenders and reacted with isocyanates to form covalent bonds between PU and GNPs. PU,Au nanocomposites were successfully synthesized, and the effects of multifunctional GNPs on the structures, morphology and properties of poly(ester urethane) were investigated. Scanning electron microscopy images suggested the GNPs can be dispersed uniformly in the PU matrix. Maltese-cross of spherical crystals was observed in the PU,Au nanocomposites, and the size of the crystals decreased with an increase in gold content. As the gold content increased, the thermal decomposition temperature and the temperature of the maximum decomposition rate increased. The glass transition temperature, crystal melting temperature and melting enthalpy of the soft segment also increased progressively. The results showed that multifunctional GNPs concentrated hard segments and resulted in an increase of heterogeneous nucleation, phase separation and elasticity. Copyright © 2010 Society of Chemical Industry [source] | ||||||||||||||||||||||