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Polymer Microstructure (polymer + microstructure)
Selected AbstractsButadiene,isoprene copolymerization with V(acac)3 -MAO.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 20074 copolymers, Crystalline, amorphous trans - Abstract Butadiene-isoprene copolymerization with the system V(acac)3 -MAO was examined. Crystalline or amorphous copolymers were obtained depending on isoprene content. Both butadiene and isoprene units exhibit a trans -1,4 structure and are statistically distributed along the polymer chain. Polymer microstructure, comonomer composition, and distribution along the polymer chain were determined by 13C and 1H NMR analysis. The thermal and X-ray behaviors of the copolymers were also investigated and compared with results from solid-state 13C NMR experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4635,4646, 2007 [source] Rhombicuboctahedral Three-Dimensional Photonic QuasicrystalsADVANCED MATERIALS, Issue 21 2010Alexandra Ledermann The aesthetics of quasicrystals has fascinated mankind already for centuries. Numerous examples are known in one and two dimensions, yet in three dimensions only icosahedral quasicrystals have been realized and observed to date in any system, i.e., in man-made, natural, photonic, and phononic quasicrystals. We rationally construct the novel class of three-dimensional rhombicuboctahedral quasicrystals and realize it as polymer microstructure. [source] Mechanistic understanding of degradation in bioerodible polymers for drug deliveryAICHE JOURNAL, Issue 12 2002Domenico Larobina A new model was developed to understand the mechanism of erosion in bioerodible polymers, which is essential to accurately predict drug release and precisely design controlled release devices. This model takes into account the phenomenon of microphase separation observed for polyanhydrides of certain copolymer compositions, and assumes that erosion is dominated by degradation and, thus, in a system with a fast eroding and a slow eroding species, two rate constants,one for each species,essentially control the evolution of the polymer microstructure. Expressions were derived for the fraction of each monomer released, as well as for the porosity in the system. A partition coefficient accounts for thermodynamic partitioning of a drug into the microdomains. The solutions of the model equations were fitted to experimental data on monomer release kinetics from two polyanhydride systems to obtain the erosion rate constants. Drug release kinetics experiments are compared to the model solution for drug release, and the partition coefficient of the drug is obtained from the fits. The comparisons to the data are promising, while pointing out the limitations of the model. The model does not account for oligomer formation prior to monomer release or for the dependence of the rate constants on parameters such as the degree of crystallinity, the local pH, and the polymer molecular weight. [source] High-molar-mass polypropene with tunable elastic properties by hafnocene/borate catalystsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2006Tanja Seraidaris Abstract Elastic polypropene has gained growing industrial and academic interest as a thermoplastic elastomer. In this study, "rac"- and "meso"-dimethylsilyl(3-benzylindenyl)(2-methylindenyl)hafnium dichloride complexes (Hfr and Hfm, respectively), activated with [NHMe2Ph][B(C6F5)4]/triisobutyl aluminum, were used in propene polymerization. Using these catalyst systems, we obtained polymers with high molar masses, up to 550 kg/mol, and moderate isotacticities between 34 and 52%. By varying the polymerization conditions, we could modify the polymer microstructure and molar mass. 13C NMR was used to calculate the polymer pentad sequence distributions. The crystalline parts of the polymers were analyzed with the differential scanning calorimetry successive self-nucleation and annealing (SSA) technique. The SSA thermograms revealed that Hfr produced polypropene with a more uniform lamellar structure than Hfm. The mechanical properties were tested with dynamic mechanical analysis creep-recovery tests. In the series, the polymers with the lowest isotacticities and therefore lowest crystallinities showed the best elastic properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4743,4751, 2006 [source] Energy Efficient Emulsion Polymerization StrategiesMACROMOLECULAR REACTION ENGINEERING, Issue 1 2008Monika Goikoetxea Abstract Polymerization strategies aiming at further reducing the environmental impact of the already "green" emulsion polymerization process were investigated. Life cycle assessment showed that non-isothermal strategies starting at low temperature resulted in an environmental impact lower than the isothermal ones. Nevertheless, the major part of the environmental impact was due to raw materials. The effect of the polymerization strategy on polymer microstructure was investigated. [source] Polymerisation of ethylene catalysed by mono-imine-2,6-diacetylpyridine iron/methylaluminoxane (MAO) catalyst system: effect of the ligand on polymer microstructurePOLYMER INTERNATIONAL, Issue 12 2002Susete Fernandes Abstract The complex, {1-{6-[(2,6-diisopropylphenyl)-ethaneimidoyl]-2-pyridinyl}-1-ethanone}iron(II) dichloride (2), has been synthesised and characterised. Treatment of complex 2 with methylaluminoxane resulted in a very active catalytic system for the preparation of polyethylene (PE). The system shows activities in the order of magnitude 107,g (PE) mol,1(Fe) h,1 bar,1. Characterisation by 13C NMR indicated that branched PE was obtained and that experimental conditions affect polymer microstructure. PE produced contained six to eight branches per 100 carbons. © 2002 Society of Chemical Industry [source] Polymerization at the gas/solution interface: Preparation of polymer microstructures with gas bubbles as templatesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Maciej Mazur Abstract We report on the chemical polymerization of 2-methoxyaniline at the interface between an aqueous solution and air. The polymer is formed in the interfacial region, whereas the soluble trimer is yielded in the bulk of the polymerization solution. The preferential polymerization of 2-methoxyaniline is discussed in terms of monomer and oligomer accumulation at the interface, which influences the reactivity of these species and allows further polymerization. The phenomenon of polymer growth is employed to selectively deposit polymeric material onto glass slides decorated with gas microbubbles. Because of preferential polymerization at the bubble/solution interface, hemispherical features are produced on the surface of glass. When some polymeric material is mechanically removed, microrings or microholes are obtained. The anomalous polymerization of 2-methoxyaniline is compared to that of 2-methylaniline. This monomer polymerizes uniformly within the entire volume of the reaction mixture; thus, no preferential polymer formation at the gas/solution interface is observed. As a result, deposition on microbubble-decorated glass slides produces polymeric films containing a number of microholes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Study on squeezing flow during nonisothermal embossing of polymer microstructuresPOLYMER ENGINEERING & SCIENCE, Issue 5 2005Donggang Yao A numerical simulation of the hot embossing process with nonisothermal embossing conditions was carried out to observe the flow pattern of poly (methyl methacrylate) into microcavities. The microcavity was isomorphically downsized. The ratio of the cavity width over the cavity thickness was maintained constant at 8:1 throughout the analysis, while the cavity thickness varied from 200 ,m to 0.5 ,m. It was found that as the microcavity was downsized, the filling mechanism varied. For larger cavity thicknesses (e.g., 100 ,m), the polymer flow climbed along the wall of the heated die and was then compressed downward and squeezed outward. In contrast, for a smaller cavity thickness (e.g., 5 ,m), the flow was uniform and the wall-climbing flow was absent. This size effect was correlated with the uniformity (UNF) of the temperature distribution of the polymer substrate during the embossing process. For larger cavity thicknesses, the high temperature zone was localized in the vicinity of the die wall, and consequently localized wall-climbing flow occurred. The size effect in nonisothermal embossing was also studied experimentally, and localized flow was observed for larger cavities but not for smaller cavities. POLYM. ENG. SCI., 45:652,660, 2005. © 2005 Society of Plastics Engineers [source] Nanostructuring polymers with cyclodextrins,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2-3 2005Cristian C. Rusa Abstract Bulk solid polymer samples formed by the coalescence of guest polymer chains from their inclusion compounds (ICs) formed with host cyclodextrins (CDs) can result in significant reorganization of their phase structures, morphologies, and even chain conformations from those more commonly produced from randomly-coiled, entangled polymer solutions and melts. When the cyclic host CDs are threaded by polymer chains to form crystalline polymer-CD-ICs, the guest polymers become highly extended due to the narrow host CD diameters (,5, 7, and 9 Å for , -, , -, and , -CDs) and are segregated from neighboring guest polymer chains by the CD-IC channel walls. As a consequence, when polymer-CD-IC crystals are treated with CD solvents that do not dissolve the guest polymers or are treated with amylase enzymes, the resulting coalesced bulk polymer samples often display properties distinct from those of normally produced bulk samples of the same polymers. In this article the CD-IC processing of polymers to generate novel polymer microstructures and morphologies are described, to control the phase separation of immiscible blocks in block copolymers, and to form well-mixed intimate blends of two or more polymers that are normally incompatible. The thermal and temporal stabilities of polymer samples coalesced from their ICs formed with CDs will also be mentioned, and it is suggested that the range of polymer properties can be greatly expanded by their CD-IC processing. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||