The correlation between the molecular mass of a nascent ultrahigh-molecular-weight polyethylene reactor powder synthesized with a postmetallocene catalyst and the specific features of plastic deformation during the orientational drawing of the material compacted and consolidated under laboratory conditions is studied. In the range 5 × 106?7 × 106, molecular mass is controlled via a change in the polymerization conditions. Under comparable conditions of orientational drawing, the highest values of strength (2.65 GPa) and the elastic modulus (100 GPa) are found for samples with M = 6.3 × 106. 相似文献
In this study, the Suzuki–Miyaura cross‐coupling reaction of naphthyl triflate with indole boronic acids catalyzed by a recyclable polymer‐supported Pd–NHC complex catalyst is presented. The polymer‐supported catalyst can be reused several times retaining high activity for the transformation. The structures of all the synthesized compounds were established by elemental analysis and from their mass, 1H‐NMR, and 13C‐NMR spectra. 相似文献
The chemistry and growth of polymer structures based on the cyanate linkage has been studied. The monofunctional model compound 2-(4-cyanatophenyl)-2-phenylpropane was used to study the reaction products. The synthesis was performed with four different transition metal catalysts and also without a catalyst. The quenched products were analyzed using Size Exclusion Chromatography(SEC) and 13C NMR. It was found that the reaction is relatively clean, with trimerization being the major product. A few side products were also detected, which included dimers and higher oligomeric species. Crosslinked polymers were synthesized without catalyst based on the bifunctional monomer 2, 2-bis(4-cyanatophenyl)propane. The structure was analyzed using 13C NMR. The conversion and number-average degree of polymerization based on 13C NMR is reported. Conversion at the gel point was found to be higher than 60%. On this basis it was concluded that polymerization based on cyanate linkages at the conditions studied is diffusion controlled and therefore not described by Flory's mean-field theory. 相似文献
Reactor powders of high- and ultrahigh-molecular weight polyethylene have been investigated. Two different Ziegler-Natta synthesis processes were used: polymerization in a slurry and in the gas phase. Synthesis temperature range was 30–85°C. Monoclinic crystals were identified in samples synthesized at 30°C. Investigations of thermal parameters were carried out by differential scanning calorimetry. A range of heating rates (0.4–10.0°C/min) was used to obtain information on sample reorganization on heating. The corresponding melt-crystallized samples were scanned and their thermal parameters were compared with those obtained from the original nascent powders. Percent crystallinity and average lamellar thickness, computed by the Thompson-Gibbs equation, were found to be controlled by conditions of synthesis. For reactor powders, the fraction of crystallinity is found to be insensitive to synthesis temperature. Crystallinity is controlled mainly by the synthesis process type: slurry or gas phase. Lamellar thickness was found to decrease as synthesis temperature was increased. This trend is the opposite of what is obtained on melt crystallization and can be interpreted on the basis of Lauritzen and Hoffman's theory of crystal growth. Nascent reactor powders give experimental support for the dependence of lamellar thickness on crystallization temperature that follows the pattern described in the theory at high undercooling. The influence of molecular weight on crystallinity and lamellar thickness of both nascent powders and melt-crystallized samples was also studied. Catalyst and synthesis conditions were found to control crystallinity and crystallite dimensions of the reactor powders. Thus, polyethylenes suitable for a specific purpose can be obtained directly on synthesis. 相似文献
Polymerization of norbornene using PdCl2 as catalyst is generally carried out at high temperatures in the absence of solvent. Low yields of polymer with relatively undefined molecular weights are obtained under these conditions. We describe the first example of polymerization of norbornene in water dispersion or aqueous emulsions catalyzed by PdCl2. Good yields of polymers and oligomers were obtained. Furthermore, in aqueous emulsions, novel microlatex which cannot be obtained by radical or ionic routes were synthesized, with particles sizes (10 nm.) generally only observed in microemulsion polymerizations.The stereochemistry of the polymers of low molecular weight was partially elucidated by13C NMR. 相似文献
Summary: A short stop reactor (SSR) was developed to study nascent particle morphology and reaction kinetics in the gas‐phase polymerisation of olefins on supported catalysts. It is shown that the SSR provides a useful means to look into important phenomena such as catalyst fragmentation and catalyst site activation and deactivation that take place during the very early stages of the heterogeneous polymerisation of olefins. New experimental results obtained from gas‐phase polymerisation of ethylene show that, depending on the type of catalyst system and on the reaction conditions, different kinds of morphologies can be obtained for the nascent polymer (e.g., cracks and folded chain). Experimental data also indicate that the growth of the polymer chains occur at a non‐steady state during the very early stages of the polymerisation.
SEM image showing the morphology of a polymer/catalyst particle after 2 seconds of polymerisation at 8 bars of ethylene on an MgCl2‐supported Ziegler‐Natta catalyst. 相似文献
High molecular weight block terpolymers with different contents of polypropylene carbonate and cyclohexene carbonate units in the polymer chain were synthesized by the copolymerization of carbon dioxide, propylene oxide, and cyclohexene oxide. Zinc adipate was used as a catalyst. The terpolymerization products were characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, GPC, DSC, and DMA methods. The influence of the reaction conditions on the composition, microstructure, and molecular-weight and thermal characteristics was studied.
The polymerization of methyl methacrylate with the VOCL3–ALEt2Br catalyst system in n-hexane has been studied. The first-order dependence of rate of polymerization on catalyst and monomer concentrations, activation energy of 6.67 kcal/mole, and NMR spectra of polymer lend support to a coordinate anionic mechanism of polymerization. It has been shown that the vanadium in V+2 oxidation state is less active than V+3 oxidation state of active complex. 相似文献
Ultra-fine zirconium carbide (ZrC) powders have been synthesized by carbothermal reduction reactions using inorganic precursors
zirconium oxychloride (ZrOCl2 · 8H2O) as sources of zirconium and phenolic resin as the carbon source. The reactions were substantially completed at relatively
lower temperatures (∼1400 °C/1 h) and the synthesized powders had a small average crystallite size (<200 nm) and a large specific
area (54 m2/g). The oxygen content of the powder synthesized at 1400 °C/1 h was less than 1.0 wt%. The thermodynamic change process in
the ZrO2–C system and the synthesis mechanism were studied. 相似文献
Bisphenylene orthocarbonate (Ⅱ) was synthesized by the reaction of dicopper catecholate with carbon tetrachloride, and underwent cationic ring-opening polymerization with the introduction of phenyl group into the main chain. The obtained polymer with ester and ether group was verified by IR and ~1H NMR spectra. Based on the analysis of the polymer structures, the polymerization mechanism was proposed. Its T_m and T_(?) are 254℃and 160℃respectively. No decomposition of the polymer was observed below 320℃. The volume expansion property of the monomer during polymerization was studied by measuring the density difference between Ⅰand its polymer at various temperatures. 相似文献
The structure of the lithium manganese tartrate precursor and the synthesis mechanism of LiMn2O4 were investigated by FT-IR, NMR, TG/DSC, and XRD in this study. The results of FT-IR and 7Li and 13C NMR measurements revealed that lithium ions bond with carboxylic acid ligands and the O–H stretching modes of tartaric acid. Manganese ion bonds only with carboxylic acid. Lithium and manganese ions were trapped homogeneously on an atomic scale throughout the precursor. Such a structure eliminates the need for long-range diffusion during the formation of lithium manganese oxides. Therefore, spinel LiMn2O4 was synthesized at temperatures as low as 300°C. In this work, the electrochemical properties of Li/LixMn2O4 were studied. It is clear that the discharge curves exhibit two pseudo plateaus as the LiMn2O4 is fired to higher temperatures. The discharge capacity of LiMn2O4 increases from 84 to 117 mAh/g as the calcination temperature increases from 300 to 500°C. The LiMn2O4 powders calcined at low temperatures with a high specific surface area and an average valence of manganese exhibit a better cycle life. 相似文献