Results 1 - 10 of 1901
Results 1 - 10 of 1901. Search took: 0.023 seconds
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[en] Novel antibacterial oxazolidinones bearing pyrrolidinone ring system at the C-5 side chain were synthesized and their in vitro antibacterial activities were evaluated. Most of the synthesized oxazolidinones showed good antibacterial activity against the Gram-positive and Gram-negative bacteria tested
[en] Pure and polyvinyl pyrrolidone blend polyethersulfone (PES) membranes were irradiated by an XeCl laser with various numbers of pulses at different fluences to investigate the changes in the surface morphology and the porosity. The results show that the membrane pore size and distribution on the surface can be modified following irradiation dependent on the laser fluence, the number of pulses and the membrane composition. These changes are very attractive for improving the membrane surface in filtration processes and biological applications. (paper)
[en] A melt crystallization process is proposed to produce high-purity n-vinyl-2-pyrrolidinone (NVP). To produce high purity products, operation strategy plays key role in the melt crystallizer. We investigated the cooling strategy and optimal sweating time using a batch-type melt crystallizer. A slow cooling followed by a slow heating was found to be an effective temperature profile to produce high purity of NVP. The optimal sweating time was found to be about 20 minutes. For industrial application, a cascade melt crystallizer which consists of four stages was constructed and the proposed crystallization/sweating scheme was applied. Using the new melt crystallizer, NVP more than 99.99% purity can be produced in semi-continuous mode
[en] An efficient small scale synthesis of 14C labeled 1-vinyl-2-pyrrolidinone (NVP) is described. The cyclization of commercially available [1,2,3,4-14C]-γ-aminobutyric acid (GABA) gives [2,3,4,5-14C]-2-pyrrolidinone which is vinylized with vinyl acetate via a sodium tetrachloropalladate catalyst to give good yields of [2,3,4,5-14C]-1-vinyl-2-pyrrolidinone. (Author)
[en] Highlights: • PA12 microspheres were prepared by a modified phase-separation process. • Polyvinyl pyrrolidone was used as a dispersant in a formic acid solution of PA12. • The microsphere diameters were controlled by adjusting the reaction parameters. • The sintering window between the onset points of Tc and Tm was greatly increased. - Abstract: Materials technology is currently a great challenge in selective laser sintering (SLS). The development of new method for the preparation of a variety of materials has drawn great attention from both industrial and academic organizations. In this work, we described a simple strategy to prepare polyamide 12 (PA12) microspheres through a modified phase-separation process. The phase separation was conducted by adding ethanol as a poor solvent into a formic acid solution of PA12 pellets with polyvinyl pyrrolidone as a dispersant. The mean diameters of the obtained PA12 microspheres, ranging from tens to hundreds of micrometers, were well controlled by adjusting the amount of ethanol and the phase separation temperature. Further investigation by differential scanning calorimetry demonstrated that the sintering window for PA12, between the onset temperatures of crystallization and melting, was drastically stretched during the microsphere formation process. The PA12 particle size and morphology, together with the wider sintering window of the microspheres, demonstrated that the obtained PA12 powder was suitable for SLS processing.
[en] The classical Charlesby-Pinner equation is reviewed and a new, general version is presented. The meaning of the virtual dose, Dv a parameter characterising deviation from the most probable distribution of molecular weight of irradiated polymer is discussed. An example of application of this modified Charlesby equation for gel-sol analysis of radiation crosslinking of vinylpyrrolidone is demonstrated
[en] Solid-liquid equilibria for mixtures composed of n-vinyl-2-pyrrolidone (NVP) and 2-pyrrolidone were measured as a basic study for the melt crystallization process to remove 2-pyrrolidone as impurity included in NVP. A differential scanning calorimeter (DSC) and a crystallizer were used and the experimental results obtained from two methods were similar. The mixture showed a eutectic system which has a single composition at the minimum melting temperature. Calculation results from simple thermodynamic equations were found in general agreements with present data. To determine the growth rate of NVP crystal which is important for the design of crystallization process, thicknesses of the crystal were measured with the time using a layer melt crystallizer. The growth rates increased as cooling temperatures decreased. Heat transfer coefficient correlated from present data was found to successfully describe the crystal growth behavior
[en] Complete text of publication follows. Radiation chemistry and in particular pulse radiolysis techniques possess unique capabilities for studying kinetics and mechanism of free-radical polymerization. These include for instance direct, time-resolved observations of early stages in polymerization processes, as well as detailed studies on propagation-depropagation equilibria. In this work a new approach to determination of propagation rate constant, kp, is discussed. Recently most studies on kp employ the IUPAC-recommended Pulsed Laser Polymerization - Size-Exclusion Chromatography (PLP-SEC). The method is based on subjecting a monomer to a series laser pulses, which initiate and terminate polymerization, and subsequently analyzing the product by SEC. Molecular weight data allow to determine kp. PLP-SEC is limited to transparent systems. Replacing laser pulses by pulses of fast electrons one can analyze kp in a broad range of systems, including non-transparent liquids or solids. This idea has been put forward by Luthjens et al. Experimental evidence of its applicability has been so far very limited. In our work we have tested this method on N-vinylpyrrolidone in water, a system recently studied in detail by PLP-SEC. Pulse irradiation with SEC analysis can precisely reproduce kp values determined by PLP-SEC at various conditions.