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Polymer Molecules (polymer + molecule)
Selected AbstractsMultimode Diffusion of Ring Polymer Molecules Revealed by a Single-Molecule Study,ANGEWANDTE CHEMIE, Issue 8 2010Satoshi Habuchi Dr. Polymergewirr: Die Untersuchung einzelner synthetischer Ringpolymere mit einer fluoreszierenden Perylendiimid-Einheit (siehe Bild, orange) in einer Matrix aus linearen Polymeren ergab, dass ein heterogenes System vorliegt. Die cyclischen Polymere sind teilweise auf die linearen Polymere aufgefädelt. [source] Copolymerization of Ethylene with 2,7-Octadienyl Methyl Ether in the Presence of Metallocene and Nickel Diimine CatalystsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2009Mércia Fernandes Abstract In this work, copolymers of ethylene with 2,7-octadienyl methyl ether have been synthesized in the presence of three single-site catalysts. The obtained copolymers not only have a polar ether function but also a double bond in the side chains that is useful for secondary reactions. The polymers were characterized by GPC, EA, DSC, NMR, and FT-IR. The catalytic activity depends on the kind of catalysts, the concentration of the polar monomer, and the concentration of the protecting agent. Up to 7.3 wt.-% of MODE could be incorporated by the metallocene catalyst. These are in average 120 functional side groups in a polymer molecule with a molecular mass of 230,000. [source] Investigation of electrical conduction mechanism in double-layered polymeric systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Prashant Shukla Abstract The electrical conduction in solution-grown polymethylmethacrylate (PMMA), polyvinylidenefluoride (PVDF) and PMMA-PVDF double-layered samples in the sandwich configuration (metal-polymer-metal) was investigated at different fields in the range 100,120 kV/cm as a function of temperature in the range 293,423 K for samples of constant thickness of about 50 ,m. Certain effects which lead to a large burst of current immediately after the application of field were observed in double-layered samples. An attempt was made to identify the nature of the current by comparing the observed dependence on electric field, electrode material and temperature with the respective characteristic features of the existing theories on electrical conduction. The observed linear I-V characteristics show that the electrical conduction follows Pool-Frenkel mechanism in PMMA and PVDF samples. Whereas, the non-linear behavior of current-voltage measurements in PMMA-PVDF double-layered samples have been interpreted on the basis of space charge limited conduction (SCLC) mechanism. The conductivity of the polymer films increased on formation of their double-layer laminates. The polymer-polymer interface act as charge carrier trapping centres and provides links between the polymer molecules in the amorphous region. The interfacial phenomenon in polymer-polymer heterogeneous system has been interpreted in terms of Maxwell-Wagner model. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Prediction of vapor,liquid equilibrium for polymer solutions based on the COSMO-SAC modelAICHE JOURNAL, Issue 10 2010Li Yang Abstract To extend the application of the COSMO-SAC model to phase-equilibrium calculations of polymer solutions, a new strategy for estimating the charge-density profile, the cavity volume and the cavity surface area of polymer molecules is proposed by finding reasonable parameters for the corresponding repeating structure units. The molecular parameters for polymers are obtained by summing up the corresponding COSMO calculated values of the repeating units calculated by the algorithms of DMol3 (a density functional theory) or MOPAC (a semi-empirical method). Combining with the COSMO-SAC model, the activities and equilibrium pressures for several typical polymer solutions are satisfactorily predicted indicating that the proposed method can be used for the prediction of vapor,liquid equilibrium of polymer solutions. It was also found that both DMol3 and MOPAC can be used though the results obtained from them are slightly different. The results in this paper show that the method proposed has the potential to predict other phase-equilibrium properties of polymer systems. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Amphiphilic PEG/alkyl-grafted comb polylactidesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2007Xuwei Jiang Abstract Amphiphilic polylactides (PLAs) with well-defined architectures were synthesized by ring-opening polymerization of AB monomers (glycolides) substituted with both a long chain alkyl group and a triethylene glycol segment terminated in either a methyl or benzyl group. The resulting amphiphilic PLAs had number average molecular weights >100,000 g/mol. DSC analysis revealed a first-order phase transition at , 20 °C, reflecting the crystalline nature of the linear alkyl side chains. Polymeric micelles were prepared by the solvent displacement method in water. Dynamic light scattering measurements support formation of a mixture of 20-nm-diameter unimolecular micelles and 60-nm particles comprised of an estimated 25 polymer molecules. UV,vis characterization of micelles formed from acetone,water solutions containing azobenzene confirmed encapsulation of the hydrophobic dye, suggesting their potential as new amphiphilic PLAs as drug delivery vehicles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5227,5236, 2007 [source] Topological polymer chemistry by electrostatic self-assemblyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2003Yasuyuki Tezuka Abstract Recent developments in topological polymer chemistry are outlined. First, nonlinear polymer topologies are systematically classified on the basis of topological considerations of constitutional isomerism in a series of alkanes (CnH2n+2), monocycloalkanes (CnH2n), and polycycloalkanes (CnH2n,2, CnH2n,4, etc.). Various pairs of topological isomers are identified in randomly coiled, flexible polymer molecules with cyclic and branched structures. An electro- static self-assembly and covalent fixation strategy has subsequently been developed for the efficient synthesis of a variety of topologically unique polymers, including monocyclic and polycyclic polymers, topological isomers, and topological block copolymers. In this process, new telechelics with moderately strained cyclic onium salt groups carrying multifunctional carboxylate counteranions have been designed as key polymeric precursors. Further extensions of topological polymer chem- istry have been achieved by the use of cyclic telechelics (kyklo -telechelics) and cyclic macromonomers, obtainable also by means of the electrostatic self-assembly and covalent fixation process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2905,2917, 2003 [source] Multicenter nature of titanium-based Ziegler,Natta catalysts: Comparison of ethylene and propylene polymerization reactionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2003Yury V. Kissin Abstract This article discusses the similarities and differences between active centers in propylene and ethylene polymerization reactions over the same Ti-based catalysts. These correlations were examined by comparing the polymerization kinetics of both monomers over two different Ti-based catalyst systems, ,-TiCl3 -AlEt3 and TiCl4/DBP/MgCl2 -AlEt3/PhSi(OEt)3, by comparing the molecular weight distributions of respective polymers, in consecutive ethylene/propylene and propylene/ethylene homopolymerization reactions, and by examining the IR spectra of "impact-resistant" polypropylene (a mixture of isotactic polypropylene and an ethylene/propylene copolymer). The results of these experiments indicated that Ti-based catalysts contain two families of active centers. The centers of the first family, which are relatively unstable kinetically, are capable of polymerizing and copolymerizing all olefins. This family includes from four to six populations of centers that differ in their stereospecificity, average molecular weights of polymer molecules they produce, and in the values of reactivity ratios in olefin copolymerization reactions. The centers of the second family (two populations of centers) efficiently polymerize only ethylene. They do not homopolymerize ,-olefins and, if used in ethylene/,-olefin copolymerization reactions, incorporate ,-olefin molecules very poorly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1745,1758, 2003 [source] RAFT Miniemulsion Polymerization Kinetics, 2 , Molecular Weight Distribution,MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2009Hidetaka Tobita Abstract The molecular weight distribution formed in a RAFT polymerization conducted inside submicron particles (Dp,<,300 nm) is considered. For small particles, the MWD at low to middle conversion might be rather broad because of the large differences in MWDs formed in different polymer particles. Such a broad MWD can be made narrower by increasing the radical entry frequency. On the other hand, larger frequencies of radical entry result in a broader MWD at the final conversion levels. The number of dead polymer chains increases with time, and the dead polymer peak could be observed in the MWD at a prolonged aging time. According to this theoretical investigation, smaller particles are advantageous in implementing a faster polymerization rate, a narrower MWD, and a smaller number of dead polymer molecules. [source] Processing/structure/property relationships for artificial wood made from stretched PP/wood-fiber compositesPOLYMER ENGINEERING & SCIENCE, Issue 1 2009Y.S. Kim This article presents the processing/structure/property relationships for artificial wood made from stretched PP/wood-fiber (WF) composites that have required strength and density. The die drawing of PP/WF composites causes a unidirectional orientation of the polymer molecules and enhances the mechanical properties significantly along the stretched direction. The drawing of the composites also lowers the density of artificial wood by generating voids at the WF and polymer matrix interface. The critical processing and materials parameters are identified. The effects of these parameters on the structure and the properties are also investigated. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source] Twin-screw compounding of poly(methyl methacrylate)/clay nanocomposites: effects of compounding temperature and matrix molecular weightPOLYMER INTERNATIONAL, Issue 8 2007Jr Hao Liaw Abstract Poly(methyl methacrylate) (PMMA)/organoclay nanocomposites prepared by melt-compounding using a co-rotating twin-screw extruder were intercalated nanocomposites. Commercially available PMMA resins of various molecular weights were used for comparison. The results showed an optimum compounding temperature for maximum intercalation with balanced shear and diffusion. Higher operating temperature reduced the shear mixing effect, and might have induced early degradation of the organoclay. Lower operating temperature, in contrast, reduced the mobility of the polymer molecules, which not only hampered the intercalation attempts, but also generated high torque in the extrusion. The mechanical behavior of the nanocomposites was studied. The tensile modulus, storage modulus and glass transition temperature of the nanocomposites increased with increasing clay content; however, an associated decrease in strength and strain at break was also observed. The notched impact strength also showed a slight decrease with clay content. Nanocomposites based on the lower molecular weight PMMA yielded more significant improvement in mechanical and thermal properties at the same clay content. Copyright © 2007 Society of Chemical Industry [source] Pan-milling mixing , a novel approach to forming polymer blends and controlling their morphologyPOLYMER INTERNATIONAL, Issue 9 2001Zhe Chen Abstract A novel technique (pan-milling mixing) was developed to control the morphology and thus enhance the mechanical properties of polypropylene/polyamide 6 (PP/PA6) systems. Through pan-milling at ambient temperature, PP/PA6 pellets of particle size 2,4,mm can be effectively pulverized to well-mixed micrometre fine powders in the solid state. During pan-milling of mixtures of PP and PA6, the polymer molecules undergo chain scission and form copolymers that compatibilize the two polymers in situ. By press moulding the finely mixed PP/PA6 powder obtained at a temperature between the melting points of PA6 and PP (for example 200,°C), a blend can be obtained in which the PA6 powder, retained throughout the process in the solid state, is well dispersed in the PP matrix. The mechanical properties of the system are much better than that of PP/PA6 blends prepared by common twin screw extrusion mixing and injection moulding. Tensile strengths of the fine PA6 particle filled PP/PA6 (70/30) blend is 29.3,MPa, which is 6.1,MPa higher than that of a conventionally prepared PP/PA6 blend. The Izod notched impact strength of a fine PA6 particle-filled PP/PA6 (70/30) blend is 6.34,kJ,m,2, which is 1.72,kJ,m,2 higher than that of a conventionally prepared PP/PA6 blend. Morphological analysis shows that the domain size of PA6 in the system is much smaller than that of the PP/PA6 blend, and can be controlled by the processing conditions such as temperature. © 2001 Society of Chemical Industry [source] Synthesis and characterization of poly(styrene-maleic anhydride)-montmorillonite nanocompositePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2002N. Salahuddin Abstract Poly(styrene-maleic anhydride)-montmorillonite nanocomposites were prepared by intercalation of layered montmorillonite with the polymer ions. Synthetic approaches including polymerization and phosphonium salt formation have been used for polymer intercalation and dispersion of the host layers in the polymer matrix. The ratio of the mineral in the composites ranged 30,50%. Wide-angle X-ray diffraction (WAXD) disclosed that the d(001) spacing between the internal lamellar surface were only expanding to about 13 and 15,Å according to the type of phosphonium salt suggesting packing of polymer molecules between the layers. Examination of these materials by scanning and transmission electron microscopy showed spherical nano size particles of average diameter, 350,nm. Copyright © 2002 John Wiley & Sons, Ltd. [source] Experimental Study on the Molecular Dimension and Configuration of Polymer and Its Flow Characteristics from Electrolyte EffectCHINESE JOURNAL OF CHEMISTRY, Issue 4 2009Xiangguo LU Abstract Molecular clew dimension and configuration of polymer, and flow characteristics of polymer solution were studied from electrolyte effect, by making use of dynamic light scattering (DLS), scanning electron microscopy (SEM), apparent viscosity method and core flow experiment. It can be observed that with the electrolyte concentration increasing, there exists a variation trend of "decreasing, increasing and decreasing again" to the molecular clew dimension of the polymer. The compression action of Ca2+ or Mg2+ to the double electrode layer of polymer molecules is more powerful by comparison against Na+, which results in that Ca2+ and Mg2+ have a more extensive effect on the viscosity of polymer solution, and clew dimensions and their distribution. With the electrolyte concentration increasing, the polymer molecular configuration of multi-layer stereoscopic random reticulation transformed into a dendritic one. During the succeeding water flooding, the variation degree of injection pressure of core was mainly determined by the swelling extent of molecular clew of retained polymer and the produced amount of polymer. And the bigger the molecular weight of polymer is, the stronger the compression or swelling action of electrolyte to the molecule clews is, and the greater the increasing degree of injection pressure during succeeding water flooding is. The greater difference of electrolyte concentrations in used water between polymer flooding and succeeding water flooding can result in greater increasing degree of injection pressure during the succeeding water flooding. So, an advisable increasing in difference of electrolyte concentrations in used water between the polymer flooding and succeeding water flooding was proposed when designing the polymer flooding performance in oilfields, which has promising result for improving effect of polymer flooding. [source] | |||||||||||||