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71.
Harald Cherdron 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):1077-1088
Abstract A review is given on two types of trioxane copolymers: trioxane/dioxolane copolymers and copolymers of trioxane with polar monomers. It has been possible to find reaction conditions that influence the transacetalization reaction and, hence, the molecular weight distribution and the sequence length of trioxane/dioxolane copolymers. Trioxane copolymers with varying dioxolane content show an unusual behavior with respect to density, specific volume, and melting point as a function of composition. This is possibly caused by the formation of at least four different crystal structures in such copolymers. The synthesis of polyoxymethylenes carrying reactive groups is possible by copolymerizing trioxane with substituted phenylglycidyl ethers. These copolymers can be subjected to further chemical modification leading to poly-oxymethylenes with aldehyde, carboxy, and amino groups or derivatives thereof. 相似文献
72.
Mostafa Mesgar Dr. Payam Kaghazchi Prof. Dr. Timo Jacob Dr. Ernesto Pichardo‐Pedrero Dr. Margret Giesen Dr. Ernesto Pichardo‐Pedrero Dr. Margret Giesen Prof. Dr. Harald Ibach Dr. Noelia B. Luque Prof. Dr. Wolfgang Schmickler 《Chemphyschem》2013,14(1):233-236
Motivated by experimental studies of two‐dimensional Ostwald ripening on Au(100) electrodes in chlorine‐containing electrolytes, we have studied diffusion processes using density functional theory. We find that chlorine has a propensity to temporary form AuCl complexes, which diffuse significantly faster than gold adatoms. With and without chlorine, the lowest activation energy is found for the exchange mechanism. Chlorine furthermore reduces the activation energy for the detachment from kink sites. Kinetic Monte Carlo simulations were performed on the basis of extensive density functional theory calculations. The island‐decay rate obtained from these Monte Carlo simulations, as well as the decay rate obtained from the theoretical activation energies and frequency factors when inserted into analytical solutions for Ostwald ripening, are in agreement with experimental island‐decay rates in chlorine‐containing electrolytes. 相似文献
73.
Sadiqali Cheruthazhekatt Harald Pasch 《Analytical and bioanalytical chemistry》2013,405(26):8607-8614
High-temperature solvent gradient interaction chromatography (HT-SGIC) is a fast and efficient fractionation technique for the chemical composition analysis of olefin copolymers. The separation of ethylene–propylene random copolymers (EPRs) was achieved on a graphitic stationary phase, Hypercarb, at 160 °C by using linear solvent gradient elution from 1-decanol to 1,2,4-trichlorobenzene (TCB). In the present work, the solvent gradient profile was modified to improve the chromatographic separation of EPRs. With the aim to obtain a better resolution in separation, a slow increase in the volume fraction of TCB was applied. This allowed for a relatively large retention region for linear polyethylene (PE) chains on the column; thereby, a broader elution volume zone between the start of the gradient and the PE elution was achieved. The efficiency of this new gradient profile was demonstrated by analysing two fully amorphous EPR samples. Clear differences in the chemical composition of these EPR samples with similar ethylene contents have been proven by using this modified solvent gradient. The comprehensive chemical composition and microstructure analysis of the SGIC-separated fractions by FTIR revealed that ethylene/propylene (EP) copolymer chains were eluted according to their ethylene/propylene contents and E or P sequence lengths, even though they are distributed in a random manner. These results showed that the solvent composition is an important factor to affect the interactive adsorption or desorption behaviour of EP chains on Hypercarb. In this way, for the first time, the determination of the complex composition and chain structure of EPR samples was achieved within short analysis time, which is not possible till now using other fractionation techniques reported. Figure
A slightly modified solvent gradient method for high-temperature solvent gradient interaction chromatography (HT-SGIC) enabled the fractionation of completely amorphous ethylene–propylene rubbers (EPR) according to their microstructure with high resolution in separation. Presence of EP copolymers having short E or P blocks was identified by combing the HT-SGIC fractionation with FTIR analysis. 相似文献
74.
Ashwell C. Makan Pritish Sinha Nyashadzashe Ngaza Werner van Aswegen Harald Pasch 《Analytical and bioanalytical chemistry》2013,405(28):9041-9047
Asymmetrical flow field-flow fractionation (AF4) was used as a fractionation technique to investigate the molecular heterogeneity of poly(styrene-b-isoprene) diblock copolymers synthesized by either sequential living anionic polymerization or coupling of living precursor blocks. AF4 coupled to multi-angle laser light scattering (MALLS), refractive index (RI), and ultraviolet (UV) detectors was used to separate the diblock copolymers from the homopolymers and coupling products, and the molar masses of the different components were analyzed. In order to get more information about the separated block copolymers, homopolymers, and coupling products, fractions were collected directly after the AF4 channel. The collected fractions were analyzed offline by 1H NMR to provide identification of the different species and additional information on the true chemical composition, and the microstructure of the diblock copolymer was obtained. Figure
? 相似文献
75.
A bicyclic diamine with defined and stable conformation in solution was prepared from Kemp's triacid. The efficient four-step synthesis of the Boc-protected diamine requires only a single purification by column chromatography. X-ray analysis and NMR spectroscopy confirm the structure of the diamine in the solid state and in solution. 相似文献
76.
Florian Capito Romas Skudas Bernd Stanislawski Harald Kolmar 《Colloid and polymer science》2013,291(7):1759-1769
The effect of low ionic strength leading to reduced polyelectrolyte–protein interactions has been shown by in silico and in vitro experiments, suggesting polyelectrolyte rigidity increasing at low ionic strength, thus leading to reduced interactions with proteins. This contribution elucidates polyelectrolyte–protein precipitation in the 0–2.6-mS?cm?1 ionic strength regime with polyelectrolyte rigidity determinations, using viscosimetry at these conditions, also considering protein charge distributions, using different proteins. Precipitation yields increased from 5 to 40 % at low ionic strength to up to 90 % at intermediate ionic strength, depending on protein and polyelectrolyte type, using lysozyme and three different monoclonal antibodies. Comparing precipitation behavior of the monoclonal antibodies, a qualitative correlation between required polyelectrolyte flexibility to enhance protein precipitation and protein average charge as well as hydrophobicity of the antibodies was discovered. Antibodies with lower average charge and less hydrophobicity required more flexible polyelectrolytes to enhance precipitation behavior by allowing interaction of the polyelectrolytes with proteins, attaching to positively charged protein patches while “circumnavigating” negatively charged protein areas. In contrast, antibodies with higher protein average charge showed increasing precipitation yields up to 90 % already at lower ionic strength, associated with then more rigid polyelectrolyte structures. Therefore, designing polyelectrolytes with specific chain flexibility could help to improve precipitation behavior toward specific target proteins in polyelectrolyte-driven purification techniques. 相似文献
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Harald Rennhofer Janea Khnke Jozef Keckes Johannes Tintner Christoph Unterweger Thomas Zinn Karl Deix Helga Lichtenegger Wolfgang Gindl-Altmutter 《Molecules (Basel, Switzerland)》2021,26(7)
Application of low-cost carbon black from lignin highly depends on the materials properties, which might by determined by raw material and processing conditions. Four different technical lignins were subjected to thermostabilization followed by stepwise heat treatment up to a temperature of 2000 °C in order to obtain micro-sized carbon particles. The development of the pore structure, graphitization and inner surfaces were investigated by X-ray scattering complemented by scanning electron microscopy and FTIR spectroscopy. Lignosulfonate-based carbons exhibit a complex pore structure with nanopores and mesopores that evolve by heat treatment. Organosolv, kraft and soda lignin-based samples exhibit distinct pores growing steadily with heat treatment temperature. All carbons exhibit increasing pore size of about 0.5–2 nm and increasing inner surface, with a strong increase between 1200 °C and 1600 °C. The chemistry and bonding nature shifts from basic organic material towards pure graphite. The crystallite size was found to increase with the increasing degree of graphitization. Heat treatment of just 1600 °C might be sufficient for many applications, allowing to reduce production energy while maintaining materials properties. 相似文献