Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Electronic Resource  (269)
  • Polymer and Materials Science  (184)
  • Life and Medical Sciences  (76)
  • Physics  (35)
  • Engineering General  (9)
  • 1
    Electronic Resource
    Electronic Resource
    Superactive and stereospecific catalysts. IV. Influence of structure of esters on MgCl2 supported olefin polymerization catalystsPart III of this series: J. C. W. Chien and Y. Hu, J. Polym. Sci. Polym. Chem. Ed., in press. (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 273-284 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CH-type catalysts were prepared by reacting MgCl2 · ROH, where ROH is 2-ethyl hexanol (EH), (R)-2-octanol (R-20), and (S)-2-octanol (S-20), with TiCl4 in the presence of di-i-butyl phthalate (BP), di-i-butyl terephthalate (BT), (-)-dimenthyl phthalate (MP), or (-)-dimenthyl terephthalate (MT). The MT catalysts were found to incorporate 8.9 to 13% Ti whereas the BP catalysts contain only 1.9 to 2.6% Ti. Comparison of the CH(EH, BP) and CH(EH, MT) catalysts showed that they have about equal number of isospecific active sites per gram of catalyst and the same rate constants of propagation for their nonspecific sites, however, the isospecific sites in the latter are less active by comparison. Consequently, the CH(EH, BP) catalysts is five times more active than the CH(EH, MT) catalysts and produces polypropylene which is 97% isotactic (reflux n-heptane insoluble) as compared to 84.7% for the latter. The catalysts derived from 2-octanols are much less active than the corresponding catalysts prepared with 2-ethyl hexanol due to lack of reactivity with phthalic anhydride which permits excessive incorporation of TiCl4 to form nonstereospecific catalytic sites as well as inactive Ti species.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280204
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Effect of polarity of the medium on the stereospecific polymerization of propylene by ansa-zirconocene catalyst (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2049-2056 
    Details
    ISSN: 0887-624X
    Keywords: metallocenes ; olefin polymerizations ; Ziegler-Natta catalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Propylene was polymerized with rac-ethylene-bis (1-η5-indenyl)dichlorozirconium/methylaluminoxane in solvents of different polarity. The poly (propylene) formed was separated by solvent extraction; 13C-NMR and DSC measurements were made on the polymer fractions. The poly(propylene) in each solvent fraction has its characteristic molecular weight steric pentad distributions, melting transition temperature, and enthalpy for fusion irrespective of the polymerization medium. The results suggest that the medium dielectric constant does not affect the polymerization rate or the intrinsic stereoselectivity, propagation and chain transfer rates a given catalytic species but can alter the occurrence of steric insertion errors through shifting of distributions of the propagating species producing poly(propylenes) of different stereoregularities. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321106
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Solid-State NMR characterization of a superactive supported ziegler-natta catalystThis is Part XXXI of the series on MgCl2-supported Ziegler-Natta catalyst. Part XXX was: J. Vizzini, F. Ciardelli, and J. C. W. Chien, “Stereoselective Polymerization of α-Olefins by Heterogeneous Chiral Ziegler-Natta Catalysts,” Macromolecules, 25, 3199 (1992). (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 48 (1993), S. 2173-2179 
    Details
    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: The formation of CH-type catalysts has been investigated by high-resolution and solid-state NMR. These catalysts are prepared from a soluble MgCl2 and 2-ethyl-1-hexanol adduct (MgCl2·3EH) by reaction with phthalic anhydride (PA) to form dioctylphthalate (DOP) and then with TiCl4 in the presence of di-i-butylphthalate (BP). In the model systems MgCl2·3EH/PA, MgCl2/BP, and MgCl2/TiCl4/BP, the ester is complexed with MgCl2 and /or TiCl4 in two or more states. Only single-ester C=O and OCH2 resonances are seen in TiCl4/BP, probably due to exchange of ester coordinations. CH-catalysts prepared by three different procedures exhibit a single mode of bonding for the ester. The chemical shift values are consistent for ester complexed with MgCl2. The most active and stereoselective catalyst has the most shielded chemical shift values for the C=O and  - OCH2 -  carbons, shortest TH1 and TH1p, and longest TCH relaxation times. These parameters change monotonically with the decrease of activity and stereoselectivity of the catalyst preparation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070481211
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Difference in stereoselective polymerization of 4-methyl-1-hexene by homogeneous and heterogeneous Ziegler-Natta catalysts (1992)
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 13 (1992), S. 479-484 
    Details
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1992.030131101
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Noncomplementarity in base sequences between the cohesive ends of coliphages 186 and λ and the formation of interlocked rings between the two DNA's (1967)
    New York : Wiley-Blackwell
    Biopolymers 5 (1967), S. 953-966 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The half molecules of 186 DNA have been isolated by the Hg(II)-Cs2SO4 density gradient centrifugal ion technique. The buoyant densities of the two halves in CsCI at 25°C. are 1.713 and 1.709 g./cm.3, corresponding to GC contents of 54% and 50%, respectively. Similarly, 5-bromouracil labeled λ DNA halves were separated. The isolation of the four DNA halves made it possible to test for homology in base sequences between the cohesive ends of λ and those of 186. There was no indication of any significant homology in base sequences between the cohesive ends of the two DNA's, as indicated by the absence of a band with intermediate buoyant density in CsCI when either half of 186 DNA was annealed with either half of 5-bromouracil labeled λ DNA and then centrifuged. The lack of cohesion between the two DNA's made it possible to demonstrate unequivocally the formation of interlocked rings (catenanes) between the two DNA's. The existence of a dimeric catenane is evidenced by the formation of a species of intermediate buoyant density when 5-bromouracil labeled λ DNA is cyclized in the presence of cyclic 186 DNA of a relatively high concentration. The molecular weight of one DNA relative to the other can be calculated from the position of the dimeric catenane in a density gradient by using the method of Baldwin. The result was in complete agreement with our previous measurements from the sedimentation coefficients and by electron microscopy. The probability of dimeric catenane formation when one DNA is cyclized in the presence of another DNA is discussed. The experimental results agree with the theoretical expectation.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1967.360051008
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    An apporach to automatic three-dimensional finite element mesh generation (1985)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 21 (1985), S. 329-347 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Recently developed solid modelling systems for the design of complex physical solids using interactive computer graphics offer the exciting possibility of an integrated design/analysis system. Called geometric modellers, these systems build complex solids from primitive solids (cubes, cylinders, spheres, solid patches, etc.) and macro solids (combination of primitives)3, 4, 8, 16, 18, 25, 38. To provide an effective structural analysis capability for these systems, methods must be devised to ease the burden of discretizing the solid geometry into a user controlled (usually locally graded) finite element mesh. The purpose of this paper is to describe an interactive solid mesh generation system capable of generating valid meshes of well-proportional tetrahedral finite elements for the decomposition of multiply connected solid structures. The system uses a semi-automatic node insertion procedure to locate element node points within and on the surface of a structure. An independent automatic three-dimensional triangulator then accepts these nodes as input and connects them to form a valid finite element mesh oftetrahedral elements. Although this report makes use of a modeller based on a constructive solid geometry representation (a so-called CSG modeller), the mesh generation strategy elaborated herein is completely general and makes no particular use of the CSG representation.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620210210
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Punch stretching of sheet metal and differential equations on manifolds (1988)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 25 (1988), S. 269-282 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The goal of mathematical modelling of sheet metal forming processes is to provide predictive tools for use in the design of stamping processes and the selection of sheet materials. Most current approaches to finite element modelling of large deformation, elastic-plastic sheet metal forming problems use a rate form of the virtual work (equilibrium) equations, and a single-field finite element representation of the displacement components. Called the incremental method, this approach does not produce approximations which satisfy the discrete equilibrium equations at all times, and consequently it demands small time steps to insure stability and numerical accuracy. This paper describes a variant of the mixed method in which displacements, stresses, effective strain and pressures are all given separate finite element representations. The equilibrium equations in non-rate form are discretized to produce a system of algebraic equations which are coupled with the constitutive equations and then integrated using state-of-the-art numerical software. When used to model rate sensitive sheet materials in hydrostatic bulging, plane strain punch stretching and hemispherical punch stretching, the new approach proved to be between 6 and 26 times as fast as the old incremental method.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620250120
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Polymer reactions, 8.Part 7: cf.3. Oxidative pyrolysis of poly(propylene)This work was supported in part by a grant No. G7-9010 from the Center for Fire Research of the National Bureau of Standards. (1980)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 181 (1980), S. 47-57 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(propylene) has been oxidized at temperatures between 240 and 289°C. The products were GC separated and on-line identified by an interfaced GC peak identification system. The major products are CO2, H2O, acetaldehyde, acetone, butanal, formaldehyde, methanol and other ketones and aldehydes. Most of the products can be accounted for by well-known reactions of alkoxyl and peroxyl radicals; the major products are derived from the secondary alkoxy and peroxy species. Oxygen starvation is manifested in diffusion limited products of olefins and dienes, and the increase of CO2 and H2O formation in pure oxygen atmosphere. The first order rate constant at 240°C is 2,4·10-3 S-1 with an overall activation energy of ca. 16 kcal·mol-1 (67 kJ·mol-1). If one assumes the oxidative pyrolysis to share the same reaction pathways as autoxidation at lower temperatures, then the observed rate constants and activation energy may be calculated from kinetic parameters measured earlier for autoxidation of poly(propylene) from 71 to 140°C. Good agreement was obtained implying a similarity of oxidative degradation of the polymers spanning a large temperature range.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1980.021810105
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Investigation on the microstructure of poly(cyclohexyl α-chloroacrylate)s using 500 MHz 1H and 25 MHz 13C NMR (1986)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 187 (1986), S. 375-381 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The tacticity of poly(cyclohexyl α-chloroacrylate) (PCCA) was studied by 500 MHz 1H and 25 MHz 13C NMR spectroscopy. The influence of the polymer configuration was observed at three different carbon resonances: The backbone methylene carbon, the carbonyl carbon and the quaternary carbon. Tetrad tacticities of PCCA measured from the resonance of the backbone methylene carbon were in good agreement with tetrad values obtained by 1H NMR. The polymer obtained was syndiotactic rich and obeyed Bernoullian statistics in its tacticity distribution.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1986.021870217
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    High mileage catalysts for olefin polymerization, 34Part 33: cf. 1. Methanolysis of titanium, vanadium and chromium olefin polymerization catalysts (1993)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 194 (1993), S. 1639-1643 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 14CH3O3H was used to quench ethylene polymerization by transition metal catalysts. 3H labeling occurred exclusively for Ti-containing catalysts, whereas more than 95% of the chains were labeled with 14CH3 for the Cr-containing catalysts. Both modes of labeling occurred with V-containing catalysts. The observed phenomena indicate a change of “coordinate-carbanionic” to “coordinate-carbocationic” character for the alkyls of Ti, V and Cr in this order.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1993.021940611
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...