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  • 1990-1994  (95)
  • 1940-1944  (5)
  • Chemistry  (81)
  • Life and Medical Sciences  (18)
  • Cell & Developmental Biology  (13)
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  • 11
    Electronic Resource
    Electronic Resource
    An investigation into the nature of the electrochemical and surface properties of polyacrylamides and a study of their adsorption onto the surface of papermaking woodpulps using alternating-current polarography (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 2875-2893 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A cationic polyacrylamide was examined using polarography, constant potential coulometry, photon correlation spectroscopy, electrocapillarity and potentiometric titrimetry. A polarographic response was found in differential-pulse polarography (DPP), direct-current and Kalousek modes at -1,7 V versus a silver/silver chloride electrode. In each case the magnitude of the response was a function of polymer concentration. However, it is thought that the response is not due to the polymer itself but impurities found with it. These were found to have a pK of 4,75. The polymer appears to develop a more open structure in LiCl solution (〈0,0013 mol/L). The unwashed polymer was found to greatly increase the interfacial tension at the mercury drop, but this effect was considerably reduced on washing the polymer in 70% acetone solution. Hydrolysis of the polymer seems to occur at pH 10. The suppression of the negative tensammetric peak of poly(ethylene glycol) (PEG200) by a range of cationic polyacrylamides was used for their analysis in the determination of their adsorption onto the surface of woodpulp. The adsorption was found to be a function of both their cationicity and mean molar mass. The rate of hemicellulose desorption from the woodpulp appears to be pH dependent. The impurity is thought to be mainly adipamic acidSystematic name: 5-carbamoylpentanoic acid..
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021921204
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  • 12
    Electronic Resource
    Electronic Resource
    The measurement of concentration and stability of weak acids and a study of the ionisation of polysaccharides using buffer capacity curves (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1741-1748 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A technique using buffer capacity has been developed for evaluating the approximate pK values of the stability constant K, of polyelectrolytes. The technique has been applied to hemicellulose extracted from woodpulp (pK ≈ 3,9 (0,1 M NaCl)) and dextran (pK = 13,55 ± 0,2 (2 M NaCl)). Verification of the method has been obtained by applying it to acetic acid (pK = 4,55 ± 0,02 (0,1 M NaCl), pK = 4,70 ± 0,02 (0,001 M NaCl)) and glucose (pK = 12,00 ± 0,05 (2 M NaCl)). Glucose was found to turn peppermint green in NaOH solutions. At least 50% of the surface charge of woodpulp was found to originate from its hemicellulose coating.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021920808
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  • 13
    Electronic Resource
    Electronic Resource
    Dynamics of a CSTR for styrene polymerization initiated by a binary initiator system (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 279-290 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: The steady state and dynamic behavior of a continuous stirred tank reactor has been analyzed for free radical solution polymerization of styrene initiated by a mixture of two initiators having different thermal stabilities. From the steady state analysis of the reactor model with a mean residence time as a bifurcation parameter, four unique regions of steady state solutions are identified in an operating parameter space for a given initiator feed composition. A variety of complex bifurcation behavior such as multiple steady states, Hopf bifurcation and limit cycles have been observed and their stability characteristics have been analyzed. The effects of feed initiator composition and the concentration of the initiator in the feed stream on the reactor dynamics are also presented.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760300505
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  • 14
    Electronic Resource
    Electronic Resource
    The thymus gland in relation to sex hormones and reproductive processes in the albino ratThis investigation has been aided by a grant from the Dr. Wallace C. and Clara A. Abbott Memorial Fund of The University of Chicago. (1941)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 68 (1941), S. 519-545 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1050680306
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  • 15
    Electronic Resource
    Electronic Resource
    Middle-ear development: II. Morphometric changes in the conducting apparatus of the chick (1992)
    New York, NY : Wiley-Blackwell
    Journal of Morphology 212 (1992), S. 257-267 
    Details
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The ontogeny of various middle-ear structures was examined in 11 groups of chicks between 10 days embryonic and adult. Measurements of the tympanic membrane surface area and height, columella length, and that of the columella footplate, annular ligament, and oval window area were obtained using video micrographs and computer digitization techniques. The oval window matures first at 53 days post-hatching, whereas the columella achieves adult size at 74 days. The tympanic membrane surface area is the last middle-ear variable studied to reach adult size (79 days post-hatch). The columella increases its length from 0.63 mm (10 days embryonic) to 2.73 mm in the adult. The tympanic membrane area expands by 280% whereas the columellar footplate area increases by 11x. As a result, the pressure amplification of the middle ear due to the tympanic membrane/columellar footplate area ratio improves by over 400%. These data further contribute to our understanding of the functional development of the middle ear. © 1992 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jmor.1052120305
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  • 16
    Electronic Resource
    Electronic Resource
    Metallocene-methylaluminoxane catalysts for olefin polymerization. V. Comparison of Cp2ZrCl2 and CpZrCl3 (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 15-38 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ethylene polymerization by Cp2ZrCl2/MAO (Cp = η5: cyclopentadienyl; MAO = methyl aluminoxane) and CpZrCl3/MAO have been studied. The MW and PD (= Mw/Mw) of polymers obtained after 2.5-60 min are the same, which indicate short chain lifetime. The values of rate constants for Cp2ZrCl2 at 70°C are: kp = 168-1670 (M s)-1 and ktrA1 = 0.012-0.81 s-1 depending upon [Zr] and [MAO,] ktrβ = 0.28 s-1, and ktrH = 0.2 M-1 torr-1/2 s-1. These chain transfer rate constant values are two to three orders of magnitude greater than the corresponding values found for MgCl2 supported titanium catalysts. One significant difference between the heterogeneous and homogeneous catalysts is that the former decays according to an apparent second order kinetics, whereas the latter decay is simple first order at 0°C and biphasic first order at higher temperatures. The productivity of the catalysts depends weekly on temperature while the MW decreases strongly with increase of temperature above 30°C. All the active species were formed upon mixing Cp2ZrCl2 with MAO while it took up to 20 min for the CpZnCl3/MAO system. The productivity of the former increase more strongly with the decrease of [Zr] than the latter. Otherwise, the two catalyst systems have all their kinetic parameters differing less than a factor of two.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280102
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  • 17
    Electronic Resource
    Electronic Resource
    Magnesium chloride supported high mileage catalysts for olefin polymerization. XXI. Isospecific and regiospecific vanadium catalyst for propylene polymerization (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 2609-2632 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several CW-V catalysts were prepared by supporting VCl4 on Mg Cl2 with ethyl benzoate and CH-V catalysts prepared by reacting MgCl2.ROH, phthalic anhydride, and VCl4. These vanadium catalysts, activated with TEA (triethyl aluminum)/MPT (methyl-p-toluate) produce mainly (88-96%) refluxing n-heptane insoluble isotactic PP. The active site has \documentclass{article}\pagestyle{empty}\begin{document}$ k_{p,i} = 1580 \left( M {\rm s} \right)^{ - 1}, k_{tr,i}^{\rm A} = 2 \times 10^{ - 3} {\rm s}^{ - 1} , k_{tr}^{\rm H} = 3.8 \times 10^{ - 2} \left( {\rm torr} \right)^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{ - 1}$\end{document} for the isospecific ones and \documentclass{article}\pagestyle{empty}\begin{document}$ k_{p,a} = 58 \left( M {\rm s} \right)^{ - 1} ,k_{tr,a}^{\rm A} = 3 \times 10^{ - 3} {\rm s}^{ -1}$\end{document} for the nonspecific sites. Catalyst of VCl3 supported on MgCl2 has comparable productivity as the VCl4/MgCl2 catalyst but catalyst of VCl2 supported on MgCl2 exhibit only one-ninth of the productivity. Extensive comparison has been made between the CW-V and the CW-Ti systems which revealed striking similarities between their polymerization behaviors. MgCl2 exerts profound influence on the stereochemical control of the vanadium ion on its activity for monomer coordination and insertion.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080281003
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  • 18
    Electronic Resource
    Electronic Resource
    Polymer precursor synthesis of alumina fibers (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 495-503 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High strength alumina fibers were fabricated with a polymer precursor process which was monitored with 13C-NMR, elemental analysis, gas evolution, SEM, and X-ray diffraction. Methylaluminoxane was chain extended by reaction with H2O, the unreacted methyl groups were converted to propanoyloxyl and i-propanoyl groups in molar ratios of 0.2 : 0.8 to 0.4 : 0.6 to afford spinning dope of adequate fluidity which can be spun into filaments with suitable stability. These precursor fibers were hydrolyzed in two stages at ambient temperatures and at 320-350°C, and then calcined at 950°C. The resulting alumina fibers have average tensile strengths up to 1.1 GPa and modulus of greater than 140 GPa.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290406
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  • 19
    Electronic Resource
    Electronic Resource
    Olefin copolymerization with metallocene catalysts. III. Supported metallocene/methylaluminoxane catalyst for olefin copolymerizationFor Parts I and II, see References 1. (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1603-1607 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Supported catalyst for fluidized bed polymerization processes has been prepared by reacting macroporous SiO2 first with MAO (methylaluminoxane) and then with Et [Ind]2ZrCl2. It contains 0.60 wt % of Zr and an [Al]/[Zr] ratio of 50. This catalyst produces homogeneous E/P (ethylene/propylene) copolymers with truly random copolymerization behaviors and required to achieve the same copolymerization activity for the Et[Ind]2ZrCl2/MAO would be required a total [Al]/[Zr] of only 670. Several time larger amount of MAO would be required to achieve the same copolymerization activity for the Et [Ind]2ZrCl2/MAO catalyst in solution. This random copolymerization is independent of catalyst concentration and composition. Activation of the supported catalyst with i-butylaluminoxane, tri-i-butylaluminum, or trimethylaluminum resulted in lower activity and copolymers having high ethylene content and crystallinity.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080291109
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  • 20
    Electronic Resource
    Electronic Resource
    Solvay type VCl3 isospecific catalysts (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1807-1817 
    Details
    ISSN: 0887-624X
    Keywords: VCl3 ; propylene polymerization ; Ziegler-Natta catalyst ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvay type S-VCl3 catalyst has 7% of catalytically active vanadium sites ([C*]) with kp (rate constant of propagation) = 31 (M s)-1 for ethylene polymerization. Addition of a comonomer, propylene of 4-methylpentene-1 (4-MP) significantly raised the ethylene polymerization activity. S-VCI3 catalyst has very small amounts of catalytically active vanadium for propylene polymerizations: [Ci*] = 0.19% with kp,i = 857 (M s)-1 and [Ca*] = 0.45% with kp,a = 23 (M s)-1 for isospecific and nonspecific sites, respectively. Addition of a conomer, ethylene or 4-MP. lowered the propylene polymerization activity. S-VCI3 is more easily reduced to the divalent ion by AIR3 than S-TiCl3. Methyl-p-toluate moderates the reducting power of AIR3; it increase the productivity and stereoselectivity of the S-YiCl3 catalyst, VCI3 supported on MgCl2 (CW-V catalyst) has enhanced rate constant of propylene polymerization but has the opposite effects on the S-TiCl3 Catalyst. VCI3 supported on MgCl2 (CW-V catalyst) has enhances rate constant of propylene polymerization but only a minute fraction of the supported vanadiums are catalytically active: [Ci*] = 0.019% and kp,i = 1580 (Ms)-1, [Ca*] = 0.057% and kp,i = 58 (M s)-1. This is compared with far greater number of catalytically active titanium sites in the TiCl3 supported on MgCl2 catalyst: [Ci*] = 6% and kp,i = 200 (M s)-1, [Ca*] = 6% and kp,a = 16(M s)-1. Therefore, both the S-VCI3 and CW-V catalysts are highly stereoselective but low in efficiency with respect to the utilization of the vanadium ion in the catalysis.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080291213
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