Author Keywords: trimethylaluminium hydrolysate; stereoregular; poly(propylene oxide); fractionation; end-group analysis; cyclic oligomers 相似文献
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71.
Partially stereoregular poly(propylene oxide) samples were synthesized via reactions catalysed by a preformed analytically defined trimethylaluminium hydrolysate. These samples were fractionated into two contrastingly different fractions.
1. (i) D-polymers: This fraction constituted the major part (up to 90%). It mainly contained cyclic low molecular weight oligomers (MW < 1000). The linear chains found in D-polymers had hydroxyl end groups. No double bonds could be detected spectroscopically.
2. (ii) K-polymers: This fraction was high molecular weight stereoregular polymer. Stepwise thermal precipitation from dilute isooctane solution of K-polymers yielded a succession of fractions which differed in melting point. It appears that the phase equilibria during the thermal precipitations were not controlled by the molecular weights of species.
72.
Summary The effect of tert-butyl chloride in the polymerizations of isobutylene carried out in the presence of SnCl4 in dichloromethane at temperatures-20°C and-78°C was investigated. Synthesized polyisobutylene samples showed a bimodal molecular
weight distribution (MWD) and it was found that the weight content of the lowermolecular weight (LMW) fraction increased with
increasing t-BuCl concentration in the polymerization mixture. The effect of ageing of the initiation mixture t-BuCl/SnCl4 in CH2Cl2 prepared in advance on MWD of the PIB samples was also studied. Ageing of the initiation system supports the formation of
the LMW fraction and this oily PIB is the only product of the polymerization at-20°C,
. 相似文献
73.
The paper deals with state estimation of the nonlinear stochastic systems by means of the unscented Kalman filter with a focus on specification of the σ-points. Their position is influenced by two design parameters—the scaling parameter determining the spread of the σ-points and a covariance matrix decomposition determining rotation of the σ-points. In this paper, a choice of the scaling parameter is analyzed. It is shown that considering other values than the standard choice may lead to increased quality of the estimate, especially if the scaling parameter is adapted. Several different criteria for the adaptation are proposed and techniques to reduce computational costs of the adaptation are developed. The proposed algorithm of the unscented Kalman filter with advanced adaptation of the scaling parameter is illustrated in a numerical example. 相似文献
74.
By means of EPR spectroscopy the behaviour of the vanadocene dichloride (I), Cp(2)VCl(2) (Cp=eta(5)-C(5)H(5)), in various deoxygenated and non-deoxygenated physiological media and therapeutic solution as well as in blood plasma and stabilized human blood was studied. On the basis of measured values of isotropic spectroscopic splitting factor g(iso) and isotropic hyperfine coupling constant A(iso), the vanadocene species, [Cp(2)V(H(2)O)Cl](+) (II; g(iso)= 1.985, |A(iso)| = 7.68 mT), [Cp(2)V(H(2)O)(2)](2+) (III; g(iso)= 1.983, |A(iso)| = 7.92 mT), [Cp(2)V(OH(2) (IV; g(iso)= 1.991, |A(iso)| = 6.285 mT), [Cp(2)VCl(DMSO)](+) (V; g(iso)= 1.985, |A(iso)| = 7.69 mT), the vanadyl species [VO(DMSO)(5)](2+) (VI; g(iso)= 1.964, |A(iso)| = 10.78mT) and [VO(H(2)O)(5)](2+) (VII; g(iso)= 1.955, |A(iso)| = 11.56 mT) have been identified. From the measurements it follows that I does not react in its first coordination sphere with any component of a system used other than water and DMSO, resp. As to water-containing media, its behaviour is fully consistent with that of I in pure aqueous media. It was found the only vanadocene species present after application of the therapeutic solution of I into human blood to be IV not interacting in its first coordination sphere with any blood component. 相似文献
75.
Oligomerization of glycine (gly) and diglycine (gly2) on montmorillonite was performed as cyclic, drying-wetting process at temperatures below 100°C, under varying reaction conditions. The influence of substrate/clay ratio, temperature and pH was found to be different for amino acid (AA) dimerization, cyclic anhydride (CA) formation and peptide chain elongation. High temperatures and neutral pH favour CA formation over diglycine production. An AA/catalyst ratio of 0.2 mmol/g leads to optimal yields. This supports the assumption that amino acid dimerization and CA formation take place at the edges of clay particles. Peptide chain elongation, starting from gly2, produces higher yields at higher temperatures and neutral pH. 相似文献
76.
This paper deals with photostabilization of low density polyethylene films (LDPE) grafted with the UV-stabilizer 2-hydroxy-4-(3-methacryloxy-2-hydroxy-propoxy) benzophenone (HMB). The influence of grafting yield and the other grafting conditions upon photostabilization efficiency of LDPE films were then studied. The chemically bound monomer (HMB) was localized mainly near the surface of an LDPE film. The grafted LDPE film was exposed to an ultraviolet radiation source, and the degree of oxidation and other photooxidative changes were determined by transmission IR and ATR IR spectroscopy. Experimental results show that radiation grafting of a UV-stabilizer upon LDPE films is an efficient photostabilization method. 相似文献
77.
Jan Kolaík 《应用聚合物科学杂志》1979,24(6):1565-1570
A freely oscillating torsional pendulum was used in the investigation of the influence of trichloroethyl, tetrachloroethyl, trichloromethoxyethyl, and trichloroethoxyethyl side groups on the molecular mobility in the glassy state and on the glass transition temperature of poly(meth)acrylates. All the polymers under study, which may be used as fire retardants, exhibit a simple relaxation behavior. While the parameters of the low-temperature and secondary relaxation process in the glassy state are not noticeably affected by the substituents used, the glass transition temperature Tg, increases with rising polarity and volume of side chains. The increase is larger in the series of polyacrylates, so that differences in the softening temperatures of polymethacrylates and polyacrylates having the same side chains decrease considerably with growing substitution. 相似文献
78.
Martin Saska Tomáš Krajník Vojtěch Vonásek Zdeněk Kasl Vojtěch Spurný Libor Přeučil 《Journal of Intelligent and Robotic Systems》2014,73(1-4):603-622
A fault-tolerant method for stabilization and navigation of 3D heterogeneous formations is proposed in this paper. The presented Model Predictive Control (MPC) based approach enables to deploy compact formations of closely cooperating autonomous aerial and ground robots in surveillance scenarios without the necessity of a precise external localization. Instead, the proposed method relies on a top-view visual relative localization provided by the micro aerial vehicles flying above the ground robots and on a simple yet stable visual based navigation using images from an onboard monocular camera. The MPC based schema together with a fault detection and recovery mechanism provide a robust solution applicable in complex environments with static and dynamic obstacles. The core of the proposed leader-follower based formation driving method consists in a representation of the entire 3D formation as a convex hull projected along a desired path that has to be followed by the group. Such an approach provides non-collision solution and respects requirements of the direct visibility between the team members. The uninterrupted visibility is crucial for the employed top-view localization and therefore for the stabilization of the group. The proposed formation driving method and the fault recovery mechanisms are verified by simulations and hardware experiments presented in the paper. 相似文献
79.
The honey bee,Apis mellifera, is one of only a few species of phytophagous insects known to be unable to convert C-24 alkyl phytosterols to cholesterol.
Regardless of the dietary sterols available to worker bees, the major tissue sterol of brood reared by the workers is always
24-methylenecholesterol, followed by sitosterol and isofucosterol. Normally, little or no cholesterol is present in honey
bee sterols. The maintenance of high levels of certain sterols is accomplished through a selective transfer of sterols from
the endogenous sterol pools of the workers to the developing larvae through the brood food material secreted from the hypopharyngeal
and mandibular glands and/or the honey stomach of the workers. The selective uptake and transfer of radiolabeled C27, C28 and C29 sterols have been studied to correlate these aspects of sterol utilization with the discovery of an unusual molting hormone
(ecdysteroid) in honey bee pupae as the major ecdysteroid of this stage of development. The phylogenetic implications of this
selective transfer phenomenon in the honey bee and comparison with sterol metabolism in certain other hymenopteran species
emphasize the diversity of steroid biochemistry in insects. 相似文献
80.
Zoltán Varga Jenő Hancsók Gábor Nagy György Pölczmann Dénes Kalló 《Topics in Catalysis》2007,45(1-4):203-206
The hydrodesulphurization (HDS) of dibenzothiophene (DBT), 4-methyl dibenzothiophene (4 M-DBT), 4,6-dimethyl dibenzothiophene
(4,6 DM-DBT) and 4,6-diethyl dibenzothiophene (4,6 DE-DBT) as real gas oil components on NiMo/Al2O3 catalyst was investigated. On the basis of the first order rate constants of HDS of the individual sulphur compounds reactivities
of the investigated compounds decreased in the order DBT ≫ 4 M-DBT > 4,6 DE-DBT ≈ 4,6 DM-DBT. Apparent activation energies
of HDS of above sulphur compounds increased from 80.0 to 120.5 kJ/mol. 相似文献