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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 57 (1962), S. 881-893 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Experimental data and a reaction scheme concerning the reaction between TiCl3 and Al(CH3)3 are presented. The reaction yielding a polymerization-active catalyst was studied in the absence of a solvent, predominantly at 65°C. The conclusion is drawn that about half of the carbon present on the catalyst is in the form of easily exchangeable CH3 groups.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 35 (1959), S. 559-561 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The surface product formed in the reaction between TiCl3 and Al(CH3)3 has been studied. Stoichiometric data, CH3/CD3 exchange, and infrared spectra permit the conclusion that the surface product is essentially a compound having the formula A model structure is proposed for this compound, valid for the 001 face of α-TiCl3. In it the titanium and chlorine atoms maintain the positions which they occupy in the α-TiCl3 lattice. One of the methyl groups protrudes from the surface whereas the other occupies the chlorine vacancy created during the reaction in the chlorine surface layer. A different sterism of the methyl groups is compatible with the experimental result that half of the methyl groups are very easily exchanged whereas the other half are not touched by the exchanging agent. According to this model it has to be assumed that the titanium atoms in the 001 plane, by far the largest face of the α-TiCl3 crystal, are not accessible. A similar model, loading to equivalence conclusions is proposed for β-TiCl3. The infrared spectra of Al(CH3)3, Al(CD3)3, AlCl(CH3)2, AlCl(CD3)2, AlCl2CH3, AlCl2CD3, TiCl3CH3, TiCl3CD3, Hg(CD3)2, and Zn(CD3)2 are discussed. Spectra of surface products formed on interaction of some of these compounds with TiCl3 are given.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 4 (1966), S. 1951-1969 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The determination of the number of sites active in the polymerization of ethylene on the surface of α-TiCl3-Al(CH3)3 dry catalysts leads to the conclusion that this number is small in comparison to the total surface of the catalyst. Qualitatively this conclusion is also reached by two other independent methods. Infrared spectra of the catalyst before and after polymerization do not show a change in the type of bonds present in the surface. Electron microscopy proves that no active sites are formed on the basal plane of the α-TiCl3 which constitutes 95% of the total surface. The results strongly favor the lateral faces of α-TiCl3 as the preferred location of active centers. The lateral faces contain chlorine vacancies and incompletely coordinated titanium atoms. This must then be the essential conditions for the formation of active centers. The propagation of the polymer chain has been repeatedly shown to follow an insertion mechanism. The active site, therefore, necessarily contains a metal-carbon bond. The study of catalysts derived from TiCl3CH3 leads to the conclusion that a Ti—C bond on titanium of incomplete coordination is the active species in these cases. The alkylation of surface titanium atoms was proven to be an intermediate step in the catalyst formation from TiCl3 and AlR3. Survival of titanium-alkyl bonds on the lateral faces, where titanium atoms are incompletely coordinated explains best, in the light of our data, the activity of Ziegler-Natta catalysts. Coordination of aluminum alkyl compounds in or around the active center probably complicates the structure of the active centers.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 4 (1966), S. 1905-1916 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction between α-TiCl3 and AlMe3 at 65°C. in the absence of solvent was studied by a method which gives information about the early stages of the reaction. The results obtained give evidence for a sequence of consecutive reactions and show that the first of these is a fast partial alkylation of the α-TiCl3 surface. The mechanism of formation of methane in the last step of the reaction is discussed in detail.
    Additional Material: 6 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 4 (1966), S. 1917-1926 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following reactions, carried out in the absence of solvents, has been studied: α-TiCl3 + Al(CH3)3 at 20°C., β-TiCl3 + Al(CH3)3 at 65°C., α-TiCl3 + Al(CH3)2Cl at 20 and 65°C., and α-TiCl3 + Al(C2H5)3 between 30 and 65°C. It appears that a general reaction mechanism, such as discussed in the preceding paper of this series, applies to all these reactions between TiCl3 and aluminum alkyls. The differences in overall stoichiometry between some of these systems may be linked to differences in stability of the intermediate Ti—C bonds. In the case of α-TiCl3 + Al(CH3)2Cl, alkylation is probably accompanied by fixation of the AlCH3Cl2 on the nonvolatile product.
    Additional Material: 1 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 4 (1966), S. 1971-1992 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental results on Ziegler-Natta catalysts, based on observations made with the electron microscope, and a qualitative comparison of the stereospecificity of various catalyst combinations are given. The polymerization of olefin in these experiments is performed in the gas phase on dry catalysts in the absence of solvent or excess aluminium alkyl. The crystallographic structure of the lateral faces of α-TiCl3 is established by electron microscopy and electron diffraction. The electron micrographs of α-TiCl3-AlMe3 catalysts show that the active centers, which are revealed by the dotwise formation of polymer, are located along the growth spirals, on lateral faces, and on surface defects. These regions of the surface are the only regions in which the surface titanium atoms are incompletely coordinated. The presence of chlorine vacancies and exposed titanium atoms is therefore an essential condition for the formation of active centers. However, the number of active centers is small in comparison to the number of incompletely coordinated titanium atoms, and hence it is concluded that the normally occurring α-TiCl3 sites with one vacancy do not yield active centers on reaction with aluminum alkyl. It is proposed that the reaction with aluminum alkyl on such sites leads ultimately to a bimetallic complex which fills the original vacancy on the titanium atom. That the complexation is reversible and that the deblocked alkylated site, which is of the type proposed by Cossee, is an active center is not excluded. Such a center would, however, give atactic polymer. Similar complex formation on a TiCl3 site having originally two vacancies would leave one vacancy on the titanium atom. This is believed to be the center of stereospecific polymerization. A model of this active center and a mechanism of polymer growth on it are proposed.
    Additional Material: 20 Ill.
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  • 8
    Publication Date: 2021-05-19
    Description: Se utiliza la información de perfiles de playa en cuatro localidades de las Playas del Este obtenidos en los últimos 27 años, para describir la tendencia de la playa a mediano plazo. A partir de datos de posición de la línea de costa y de volúmenes de arena de la playa emergida se estableció la tasa de cambio de la playa utilizando la regresión lineal simple. Los resultados confirman la tendencia erosiva de un sector de la playa de Guanabo. La tasa anual de retroceso de la línea de costa ha sido de -0.97 m/año que ha establecido un cambio total de - 26 ±7 m. La reducción de los volúmenes de arena ha sido de -28 ± 8 m3/m, a un ritmo de -1.04 m3/m/año. En la playa de Santa María, la línea de costa en algunas localidades ha experimentado retroceso y en otras ha ocurrido poco cambio, sin embargo en todos los casos se ha producido un incremento notable en los volúmenes de arena de la playa emergida debido a la formación y crecimiento de las dunas. La reactivación de los procesos eólicos que dio lugar al restablecimiento de la morfología de dunas fue posible por la eliminación del bosque de casuarinas que, durante más de 20 años, ocupó la zona posterior de la playa.
    Description: The information of beach profiles, obtained during the last 27 years in four localities of Playas del Este, is used to describe the medium-term tendency of the beach. Starting from data of the shoreline location and sand volumes of the emerged beach, the beach change rate was established applying simple linear regression. The results confirm the erosive tendency of a sector in Guanabo beach. The annual rate of shoreline retreat has been -0, 97 m/y, which has established a total change of - 26 ± 7 m. The reduction in sand volumes has been -28 ± 8 m3/m, at a rate of -1,04 m3/m/y. In Santa Maria beach, the shoreline has experienced retreat in some localities or little change in the others. However, a remarkable increase in sand volumes of the emerged beach has taken place in all the cases. The reactivation of Aeolian processes, resulting in the reestablishment of dune morphology, was possible due to the removal of the Australian pine forest that had occupied the area from the beach top landward for more than 20 years.
    Description: Published
    Description: playas, evolución a mediano plazo, regresión lineal, beach, medium- term evolution, lineal regression.
    Keywords: Dunes ; Beach morphology ; Beach erosion ; Dunes
    Repository Name: AquaDocs
    Type: Journal Contribution
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