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  • 1
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A gas-phase reactor system was developed to polymerize ethylene using the MgCl2/ethyl benzoate (EB)/TiCl4+ triethylaluminum (TEA) catalyst. The reproducibility of the reactor was tested and found to be adequate for kinetic study. The effects of TEA and temperature were studied with the multisite model that assumes a multiplicity of active sites. It was found that the productivity increased with Al/Ti molar ratio while initial activity leveled off. The deactivation rate, after an initial increase, Al/Ti molar that assumes a multiplicity of active sites. It was found that the productivity increase, decreased with Al/Ti. This corresponded with a transition in deactivation order: below Al/Ti = 70, first-order deactivation was predominant; above Al/Ti = 70, second-order deactivation was predominant. The second-order deactivation reactions were made less disperse at higher Al/Ti. Molecular weight of the polyethylene was very high (〉 1,000,000) indicating negligible transfer reactions. For Al/Ti 〉 130 a monomer sorption limitation for polymerization was found. The effect of temperature was also studied with a maximum in productivity at 55°C for Al/Ti = 98.0 and no maximum when Al/Ti = 53.0. Apparent activation energies (Ea) for activity were found to be 19.5 ±3.3 kJ/mol at Al/Ti = 98.0 and 9.3±1.1 kJ/mol at Al/Ti = 53.0. for deactivation Ea was found to be 36.6±5.0 kJ/mol at Al/Ti = 98.0 and-15.5± 4.4 kJ/ mol at Al/Ti = 53.0. Temperature increased the dispersity of second-order deactivation reactions. © 1993 John Wiley & Sons, Inc.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 1229-1235 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Slurry polymerization of propene using MgCl2-supported TiCl4/dioctylphthalate catalysts were carried out in a semibatch reactor at a constant pressure to examine the effects of polymerization conditions on catalyst activity and polymer isotacticity. The catalysts were prepared at 80, 90, and 105°C, which gave different compositions of chemical complexes associated with the diester. Five alkyl aluminums (triethyl, triisobutyl, tri-n-hexyl, tri-n-octyl, and isoprenyl) were studied as cocatalysts. Among these, triethyl aluminum was found to be most effective for the catalysts prepared at 80 and 95°C, and tri-n-hexyl aluminum for the catalyst prepared at 105°C. Dimethoxydiphenyl silane and 2,2,6,6-tetramethylpiperidine were employed to study their effects as an external Lewis base for the catalyst prepared at 105°C. In both cases, a small amount of either base resulted in significant increase in activity and isotacticity, which can be attributed to the high level of phthaloyl chloride complex in the catalyst. © 1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Propene was polymerized over the MgCl2-supported TiCl4/dioctylphthalate catalyst in heptane. Polymer products obtained under different polymerization conditions were separated into isotactic and atactic polypropenes by the extraction of boiling n-heptane. The effects of polymerization time, cocatalyst type, cocatalyst/catalyst ratio, polymerization temperature, and external base/cocatalyst ratio on the isotactic triad of the isotactic portion of polypropene were investigated 2,2,6,6-Tetramethyl piperidine (TMPIP), dimethoxy diphenyl silane (DMDPS), and t-butylmethyl ether (TBME) were employed as the external Lewis base. High concentrations of the first two bases caused a decrease in isotactic triads in the isotactic polymer, while TBME showed no significant effects. The difference can be attributed to the different roles these external bases play in polymerization. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In propene polymerization over the MgCl2-supported TiCl4/dioctylphthalate (DOP) catalyst, the weight- and number-average molecular weights and the molecular weight distribution (MWD) of polypropene products and of the isotactic and atactic polymer portions were studied. The average molecular weights and MWD were found to be independent of time. The isotactic polymer had higher molecular weight and broader distribution than the atactic portion by almost an order of magnitude. An increase in temperature and cocatalyst/catalyst ratio resulted in lowering molecular weight due to increasing transfer reaction. Alkyl aluminum was used as a cocatalyst, and the molecular weight did not vary significantly with different alkyl groups. Of the three external bases studied, 2,2,6,6-tetramethyl piperidine (TMPIP), dimethoxydiphenyl silane (DMDPS), and t-butylmethyl ether (TBME), the addition of a small amount of one of the first two bases caused a substantial increase in both molecular weight and polydispersity of the isotactic polymer. Those increases leveled off quickly with increasing amounts of the external base. On the other hand, both average molecular weights and polydispersity of the atactic polymer decreased with a net increase in the molecular weight of the whole polymer. TBME, however, has no significant effect on either molecular weight or MWD. These effects are discussed in the context of the roles of the external base in propene polymerization. © 1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The aging of the MgCl2/dioctyl phthalate (DOP) or ethyl benzoate (EB)/TiCl4 catalyst was studied. Because of the strong complexation of DOP with the catalyst, only a small fraction of DOP was extracted by cocatalyst triethylaluminium (TEA) during aging, resulting in converting some highly isospecific sites into aspecific ones. No change of the overall number of sites was detected. EB, on the other hand, could be readily removed by TEA, resulting in a large increase in aspecific sites. Clustering of those sites facilitated catalyst deactivation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: High activity TiCl4/MgCl2/ethyl benzoate (EB)/triethyl aluminum (TEA) catalysts for the polymerization of propylene were synthesized and characterized for particle size distribution and crystallinity. Polymerization was carried out in a semibatch, constant pressure slurry reactor. A correction for interfacial mass transfer was found to be necessary to relate the monomer feed rate to the instantaneous rate of polymerization. Without such a correction serious misinterpretation of rate data could result. Optimum productivity was observed with respect to the Al/Ti ratio. Similar behavior was observed with polymerization temperature. Isotacticity increased with polymerization tamperature and decreased with Al/Ti ratio. The addition of a small amount of 2,2,6,6-tetramethylpiperidine increased the percentage of isotactic polypropylene to 98% without significantly affecting productivity.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In propylene polymerization over TiCl4/MgCl2/ethyl benzoate (EB)/triethyl aluminum (TEA) catalysts, experimental evidence strongly suggests that active sites have differing propagation and termination rate constants. Although the chemical structure of these sites may be quite similar, their location on the support may affect their polymerization activity, and this results in a distribution of the propagation and deactivation rate constants. To model this type of system, we developed a kinetic model accounting for multiple active sites. The model was fitted to simulated polymerization data to investigate the validity of mathematical approximations used in the derivation of the model equation. Using experimental data, the adequacy of the model was tested, and the statistical inference of parameter estimation was also discussed. The effects of experimental operating variables and additives on the kinetic model parameters revealed an important insight into the fundamentals of this system. The optimum productivity commonly observed has been shown to be the result of differing rates of increase of both propagation and termination rates with Al/Ti ratio and temperature. Kinetic evidence also suggests that the additive selectively poisons atactic-specific sites.
    Additional Material: 15 Ill.
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  • 9
    ISSN: 1520-5134
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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