A series of segmented block copolymers of NR and 1,3-butanediol–toluene diisocyanate oligomers have been synthesized with varying hard segment content. The synthesis has been carried out by one-shot and two-shot processes in solution. The products were characterized by spectral analysis, thermal and mechanical analysis, SEM and optical microscopy. They are found to be amorphous materials having no potential for hydrogen bonding between the ‘hard' and ‘soft' segments. Their two-phase morphology has been deduced from SEM and optical micrographs and established by DMA and thermal studies. DSC analysis shows a soft segment glass transition temperature at −62±2°C and hard segment glass transitions between 70° and 100°C, depending on the polyurethane content. The Tg values determined by the dynamic mechanical analysis are significantly higher than these values.
The thermogravimetric analysis indicates a two-stage thermal decomposition of the materials by random nucleation mechanism and corresponds to the two phases present in the block copolymer. Depending on the proportion of the continuous and dispersed phases, the block coolymers behave like quasi-elastomers at lower hard segment concentrations and brittle plastics at higher hard segment contents. This variation in mechanical behaviour is consistent with the sample morphology. Materials synthesized by the two-shot process are found to possess better mechanical properties than the one-shot products, presumably due to a more systematic ordering of the different segments in the former. 相似文献
Cu–ZnO and Mn–Cu–ZnO catalysts have been prepared by electrodeposition and tested for the synthesis of higher alcohols via CO hydrogenation. The catalysts were prepared in the form of nanowires and nanotubes using a nanoporous polycarbonate membrane, which served as a template for the electrodeposition of the precursor metals from an aqueous electrolyte solution. Electrodeposition was carried out using variable amounts of Zn(NO3)2, Cu(NO3)2, Mn(NO3)2 and NH4NO3 at different galvanostatic conditions. A fixed bed reactor was used to study the reaction of CO and H2 to produce alcohols at 270 °C, 10–20 bar, H2/CO = 2/1, and 10,000–33,000 scc/h gcat. In addition to methane and CO2, methanol was the main alcohol product. The addition of manganese to the Cu–ZnO catalyst increased the selectivity toward higher alcohols by reducing methane formation; however, CO2 selectivity remained high. Maximum ethanol selectivity was 5.5%, measured as carbon efficiency. 相似文献
Noble metal thin films (Pt and Ru) were grown at 250 °C, using commercially available precursors, by the pulsed spray evaporation chemical vapor deposition (PSE-CVD) technique. The growth process relies on the thermally activated reaction of ethanol with the metal acetylacetonate precursors. The synthesized polycrystalline films are pure metal phase and crystallize in hexagonal (Ru) and cubic (Pt) structures. The formation of an interfacial silicide phase was noticed in the case of the Pt growth on silicon substrates. The films are smooth, continuous and show a steady growth without any noticeable incubation time. The single-step growth of Pt-based alloys, Pt–Co and Pt–Cu, with controlled composition was performed by simply adjusting the composition of the liquid feedstock. 相似文献
In this study, we presented an unexpected environmentally benign and easy-to-implement reaction for producing highly pure hydrogen (99.8%) and value-added carboxylate from primary alcohols under basic conditions. No catalyst was required, and no environmentally harmful gas, such as CO and CO2, was produced. The reaction conditions, different reactants and the water tolerance of the reaction were examined. It was found that as long as the temperature is higher than 500 K, no matter what the pressure is, hydrogen and carboxylate can be produced from primary alcohols. Strong alkalinity and high solubility of the base is necessary for the reaction. It was confirmed that ethanol-water mixtures, which could be produced from biomass fermentation, can be used as feedstock in this process, making it more meaningful in terms of sustainability. The mechanism of the reaction was also investigated in detail. 相似文献
The possibility of shape-selective resistive gas sensors for polar molecules using the microporous alumo-silicate Stilbite
is investigated. The electrical impedance of natural Stilbite single crystals at 80°C decreases in presence of methanol, 2-propanol and 3-pentanol, but increases with increasing water and neo-pentanol vapour
pressure. The interaction can be described by a Langmuir-type adsorption equation. The conductivity effects are interpreted
mainly by mobility effects, due to sterical interactions in the zeolite channels. 相似文献
The cyclopropenone activated dehydration reaction of alcohols is a promising alternative to alcohol substitution reactions to avoid hazardous byproducts and harsh reaction conditions. Density functional theory calculations at M062X/6–31 + G(d,p) level were performed for two proposed reaction mechanisms of the cyclopropenone activated chlorodehydration reaction where alkyl chloride product can be obtained from both of the proposed reaction mechanisms but chloroxalate has only one alternative. The calculations enabled us to explain the rection mechanisms in detail. Additionally, the effects of the various substituents on the cyclopropenone ring for the product distribution ratio was clarified.The substitution with electron donating group on para position of the phenyl ring of cyclopropenone has no effect on the relative free energy of the rate-determining step where the electron-withdrawing group increase the energy values independent from the position. The product ratio values that were calculated from energy barriers are in harmony with the experimentally obtained ones pointing out the reaction mechanism preference. 相似文献
The self-organization and aggregation behavior of a surface active ionic liquid (SAIL) 1-methyl-3-octylimidazolium chloride [C8mim]Cl, was investigated in aqueous solutions of alcohols 1,2-propanediol and 1-propanol in different compositions using conductivity, surface tension and fluorescence measurements at room temperature. This surface active ionic liquid was synthesized by the reaction of 1-methylimidazole with 1-chlorooctane. Fluorescence spectroscopy was employed to get detailed insight into the local microenvironment of the aggregates, critical aggregation concentrations (CAC) and aggregation number (Nagg.). Degree of ionization (α), CAC and various thermodynamic parameters like the standard Gibbs free energy of aggregation (ΔGagg.0), standard enthalpy of aggregation (ΔHagg.0) and standard entropy of aggregation (ΔSagg.0) were calculated using conductivity measurements at different temperatures (288.15, 298.15 and 308.15 K). The surface activity of the IL in various mixed solvents was evaluated from surface tension measurements by calculating various surface parameters like the minimum surface area occupied by a single ionic liquid molecule (Amin), adsorption efficiency (pC20), maximum excess concentration at the surface (Γmax), effectiveness of surface tension reduction(ΠCAC), surface tension at CAC (γCAC), p (packing parameter) and CAC at different compositions. Increases in the CAC values were observed with the increase in the amount of alcohols which is attributed to the balancing between electrostatic and hydrophobic interactions. The results from different techniques show that the CAC increases with increase in the amount of the alcohol which is due to the solubilization of the IL molecules which delays the aggregation process. This shows that the spontaneity of the aggregation process of IL decreases with the increase in the concentration of alcohols in water. 相似文献