The effect of commonly used induced condensing agents (ICAs) on the rate of polymerization of ethylene on a supported Ziegler–Natta catalyst in a gas‐phase process is investigated. It is observed that the instantaneous rate of ethylene polymerization is promoted in presence of all ICAs studied. This is attributed to the effect of the heavy ICAs in enhancing the local concentration of ethylene at the active polymerization sites that are dispersed within the growing polymer particles. It is found that the higher the solubility of ICA in the polymer, the greater the observed effect. It is also observed that the enhancement due to the presence of an ICA is greater during the initial phase of the polymerization.
Inert condensing agents (ICAs) are used principally to cool down gas‐phase fluidized bed reactors used to polymerize ethylene over supported catalysts. While these ICAs are chemically inert, it appears that they might nevertheless increase the polymerization rate. n‐Hexane is used as an ICA, and an enhancement in the instantaneous rate of ethylene polymerization in the gas phase is observed. This is attributed to a rise in the local ethylene concentration in the amorphous polymer phase surrounding the active sites, due to increases in both the solubility and diffusivity of ethylene in the amorphous polymer. In addition, the polymer particles have a smoother surface with less formation of fiber‐like substructures as the n‐hexane concentration increases.
Summary: A new procedure was developed to support [(ArN?C(Me))2C5H3N]FeCl2 (Ar?2,4,6‐trimethylphenyl) on spherical MgCl2 for ethylene polymerization. The resultant catalysts showed ten times higher activity of the corresponding catalyst in homogeneous catalysis. The morphologies of polyethylene particles strongly depended on supported catalyst preparation procedure and polymerization conditions. In addition, the GPC measurements showed bimodal polyethylene for the homogeneous polymerization while mono‐modal polyethylene of those supported catalysts.
EDX Line Scan analysis of the catalyst SMSIC‐1 regarding the aluminium and iron distribution in the volume (25 kV accelerating voltage, magnification 1 500). 相似文献
The number of active centers (CP) and propagation rate constant (kP) for ethylene polymerization with homogeneous catalyst LCoCl2 + MAO and supported catalyst LCoCl2/SiO2 + Al(i‐Bu)3, where L is 2,6‐(2,6‐(Me)2C6H3N = CMe)2C5H3N, have been determined using the method of polymerization quenching by radioactive carbon monoxide (14CO). The unstable rate profile of the reaction was attributed to a decrease in the number of active centers from 0.23 to 0.14 mol · mol?1(Co) corresponding to an increase in the reaction time from 5 to 15 min, whereas the kP value remained constant, amounting to 3.5 × 103 L · mol?1 · s at 35 °C. A narrow molecular weight distribution of the obtained polyethylene (PE) samples ( = 1.9) testifies that the homogeneous catalyst LCoCl2 + MAO can be regarded as a single‐site system. The activity of the supported catalyst was stable and noticeably lower than that of the homogeneous catalyst due to the low concentration of the active centers (0.02–0.03 mol · mol?1(Co)). PE with a broad molecular weight distribution ( = 36) and noticeably higher molecular weight is formed in the presence of the supported catalysts. The activity of the supported catalyst increases sharply at polymerization in the presence of hydrogen. The data obtained on the CP and kP values allow suggesting the formation of the “dormant” centers at polymerization without hydrogen and regeneration of the active centers in the presence of hydrogen. The average kP values for the supported catalyst containing multiple active centers were determined to be 5.9 × 103 and 10.5 × 103 L · mol?1 · s, respectively, at 35 and 50 °C.
The RAFT polymerization of styrene in a solvent consisting of a water/alcohol mixture with different water contents is performed and the solvent effects on polymerization kinetics, polymer chain propagation, and polymer particle growth are evaluated. It is found that the solvent affects the RAFT polymerization kinetics greatly, and the apparent polymerization rate constant (Kpapp) increases with an increase in the water content of the water/alcohol mixture. In addition, RAFT polymerization in a water/alcohol mixture with a higher water content affords better control of the polydispersity index (PDI) of the synthesized polymers. Furthermore, the solvent also exerts a great influence on the growth of the polymer particles. Hollow particles are formed either at the initial polymerization with low monomer conversion or in the solvent with a low water content, whereas solid polymer particles are produced either at high monomer conversion or in the solvent with a high water content.
In this work (Part II) the application of new polystyrene based microcarriers in cell culture technology is demonstrated. Carriers with a variety of surface modifications were tested as a growth support for cell line BHK 21. The growth behavior of the cells and cell to surface attachment were compared to Cytodex 3 (Pharmacia), which was used as a reference carrier. To select carriers with growth supporting surfaces, broad screening in petri dish experiments was carried out. Candidates with the highest growth rates were investigated in spinner flask experiments in further detail. Polystyrene carrier with a surface modification like triethylamine, maltamine or N-methylglucosamine were able to support growth as good or better as the reference carrier Cytodex 3. Economies of ingredients and ease in laboratory handling could make amine-modified polystyrenes a competitive alternative to currently commercially available microcarrier types. 相似文献
The three-dimensional structure of the transverse-axial tubular system, sarcoplasmic reticulum (SR) and mitochondria in the extracapsular region of the intrafusal muscle fibers of the rat lumbrical muscle was observed by ultra-high-resolution scanning electron microscopy after removal of the cytoplasmic matrix by the osmium-DMSO-osmium procedure. Nuclear chain fibers possessed thick to moderately sized column-forming mitochondria with occasional I-band branches. The transverse tubules (T-tubules) running at the level of the A-band side of the A-I junction were sandwiched between two large terminal cisternae for most of their length, forming triads. The sarcotubules arising from the terminal cisternae formed single-layered networks at the A-band level, and well developed, double-layered, three-dimensional networks at the I-band level. Nuclear bag1 fibers possessed slender column-forming mitochondria devoid of I-band branches. The T-tubules were located at the level of the A-I junction. Both the T- and the axial-tubules were occasionally coupled with small terminal cisternae, forming dyads or triads. At the I-band level, the SR was well developed and formed single layered networks, but at the A-band level only a few longitudinally arranged sarcotubules and axial tubules were observed. Nuclear bag2 fibers contained medium to large diameter column-forming mitochondria without I-band branches. The T-tubules ran at the level of the A-band adjacent to the A-I junction, and were coupled at some intervals with terminal cisternae of various lengths. Swollen, large terminal cisternae were frequently seen.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
There has been a re-emergence of the use of lectins in a variety of therapeutic venues. In addition lectins are often responsible for the binding of pathogens to cells and for cancer cell clumping that increases their escape from body defenses. It is important to define precisely the activity of inhibitors of lectin-binding that may be used in anti-infection and anti-cancer therapeutics. Here we describe a kinetic assay that measures the activity of saccharide inhibitors of lectin binding using a model system of yeast (Saccharomyces cerevisiae) and lectin (Concanavalin A, Con A) derivatized agarose microbeads that mimics pathogen-cell binding. We show that old methods (part I of this study) used to identify inhibitor activity using only one sugar concentration at one time point can easily provide wrong information about inhibitor activity. We assess the activity of 4 concentrations of 10 saccharides at 4 different times in 400 trials and statistically evaluate the results. We show that d-melezitose is the best inhibitor of yeast binding to the lectin microbeads. These results, along with physical chemistry studies, provide a solid foundation for the development of drugs that may be useful in anti-infectivity and anti-cancer therapeutics. 相似文献
Summary The validity of the pedometer and actometer for estimating the daily physical activity was evaluated by means of an observation study. The physical activity in a classroom of 11 pupils of a kindergarten was assessed by means of a pedometer, actometer and by observation. Besides this an activity questionnaire was completed by the infant-quide. On basis of the individual observation it is clear that the infant-guide can give valuable information about the activity of the children at school.The results of the pedometer attached to the waist and the actometers attached to the ankle were significantly correlated with the results of the observation method. The wrist actometer showed a smaller but still significant correlation with the other variables. Implications of this findings are discussed in regard toward the physical activity. The pedometer results point out that when the percentage of intense activity is high the pedometer tends to underestimate the level of activity.The actometer results indicate that such a motion recorder gives a reliable estimation of activity in children. The findings are discussed in terms of the practical applications of the actometer in the research of daily physical activity and the physical rehabilitation treatment of certain diseases. 相似文献
ABSTRACT: In the previous paper we have demonstrated that progesterone-treated lymphocytes of healthy pregnant women produce a 34,000 MW protein that inhibits cytotoxic activity and prostaglandin F2α synthesis. Since recently it has been shown that certain leukotrienes have a stimulatory effect on natural killer activity, in this study an attempt was made to determine whether there is a relationship between cytotoxicity and PGF2α synthesis or if alterations in the values of these parameters are independent. Arachidonic acid increased cytotoxic activity of healthy pregnant women's peripheral blood mononuclear cells (PBMC) in a concentration-dependent manner. Exogenous arachidonic acid was able to counteract the blocking effect of the above-mentioned protein produced by progesterone-treated lymphocytes. To determine whether the products of the cyclooxygenase or the lipoxygenase pathway of arachidonic acid metabolism are responsible for increased cytotoxicity, both enzyme systems were blocked separately. Both indomethacin and the lipoxygenase inhibitor BW 755C reduced cytotoxicity in a dose-dependent fashion. However, the lipoxygenase inhibitor prevented prostaglandin synthesis to the same extent, or even more than indomethacin, in all concentrations used; so, its blocking effect cannot be considered as supportive evidence for the role of leukotrienes in cytotoxicity. On the other hand, lipopolysaccharide, with a selective stimulatory effect on prostaglandin synthesis, increased cytotoxicity. Lipopolysaccharide had no effect on progesterone-pretreated PBMC. The above data allow the assumption that besides leukotrienes, cyclooxygenase products may also increase cytotoxicity. 相似文献
Three 2,5‐substituted polar PPV derivatives have been prepared using the sulfinyl precursor route and compared to the apolar MDMO‐PPV. All polymers were obtained in excellent yield and with improved purity as compared to other methods. The influence of the polarity of the side chains, i.e. oligo(oxyethylene) and alkyl substituents, on the optical and electronic properties were investigated. In thin films, the oligo(oxyethylene) substituents do not significantly alter the optical properties of the conjugated backbone and the field effect mobility. In contrast, other thin film electrical properties, such as relative permittivity and conductivity, are markedly affected by the polar substituents. This is also the case for their solubility and solution properties. The polar PPV‐derivatives are not only soluble in a wide range of solvents, but also exhibit aggregation phenomena.
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