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  • Polymer and Materials Science  (14)
  • Bronze Age  (2)
  • Density functional calculations  (2)
  • Transition states  (2)
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  • 1
    Digitale Medien
    Digitale Medien
    Prehistoric land use as recorded in a lake-shore core at Lake Constance (1993)
    Springer
    Vegetation history and archaeobotany 2 (1993), S. 213-232 
    Details
    ISSN: 1617-6278
    Schlagwort(e): Human impact ; Lake Constance ; Neolithic ; Bronze Age ; Climate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Klassische Archäologie , Biologie
    Notizen: Abstract The second part of a pollen profile from Hornstaad/Lake Constance (Germany), containing the Atlantic and Subboreal (6400 cal B.C. to 700 cal B.C.) is presented. The diagram has a sampling interval of 1 cm and an average time resolution of 10 years. The cereal curve provided the basis for cereal zones, which are used to classify the human impact. Twenty-six cereal zones can be distinguished, most of them divided into subzones, from 5500 cal B.C. to 700 cal B.C. They correspond to both known and, mostly, unknown settlements in the surrounding landscape from the Early Neolithic to the Late Bronze Age. Charcoal and chemical analyses as well as sediment accumulation, confirmed by accelerator dates, provide evidence for human impact on the environment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00198163
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  • 2
    Digitale Medien
    Digitale Medien
    New approaches to prehistoric land-use reconstruction in south-western Germany (1996)
    Springer
    Vegetation history and archaeobotany 5 (1996), S. 65-79 
    Details
    ISSN: 1617-6278
    Schlagwort(e): Late Neolithic ; Bronze Age ; Germany ; Prehistoric farming ; Cultural landscape
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Klassische Archäologie , Biologie
    Notizen: Abstract Botanical on-site and off-site data relating to Late Neolithic and Bronze Age settlement phases in south-western Germany are compared with a view to reconstructing economic and environmental change. The large differences between the Neolithic and Bronze Age as regards forest composition, crops and crop weeds, and charcoal input are explained in terms of different types of agronomic systems and hence cultural landscape. In the Late Neolithic, shifting cultivation, involving slash and burn, was practised with the result that the landscape was largely dominated by tall shrubs. In the Bronze Age there were more or less permanent arable fields with only short fallow phases. The agronomic system and the resulting cultural landscape was already similar to that of the medieval period and, especially, early medieval time.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00189436
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  • 3
    Digitale Medien
    Digitale Medien
    Progress in synthesis and application of segmented polymersDedicated to Prof. Dr. H. Sinn on the occasion of his 65th birthday (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 47-60 
    Details
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Maßgeschneiderte segmentierte Polymere spielen eine Schlüsselrolle bei der Entwicklung von neuen polymeren Materialien. In Abhängigkeit von den molekularen Architekturen der segmentierten Polymeren kann die Ausbildung von Polymermorphologien und von Eigenschaftssynergien gesteuertwerden. An ausgewählten Beispielen werden grundlegende Konzepte und neuere Entwicklungen vorgestellt. Segmentierte Silikon-Flüssigkautschuke, wo unverträgliche Silikonsegmente von zwei mischbaren Oligo(caprolacton)-Segmenten flankiert werden, sind wirkungsvolle Zähmodifikatoren für Epoxidharze. In nanophasenseparierten IPNs auf Basis dieser Silikon-modifizierter Epoxidharze kann die Schlagzähigkeit ohne Verlust der Dimensionsstabilität erhöht werden. Kompatibilisierte Blends aus segmentierten phenolischen Polyurethan- und epoxidfunktionellen Nitril-Flüssigkautschuken bilden diskrete Blend-Mikrophasen, die in Epoxidprepregs dispergiert sind und strukturelles Verkleben von Aluminium in Faser-Metall Laminaten ermöglichen. Reaktive Blendtechnologien werden entwickelt, um während der Polymerverarbeitung, z.B. von Polypropylen/Polyamid 6 Blends, in-situ Phasenvermittler herzustellen. Durch Einbau von definierten Oligo(tetrafluoroethene) Segmenten in Kodensationspolymere werden neben thermischen und mechanischen Eigenschaften auch Oberflächenspannungen und Gasdurchlässigkeiten variiert.
    Notizen: Tailor-made segmented polymers play a key role in the development of novel polymeric materials exhibiting unsual bulk and surface properties. As a function of molecular architectures of segmented polymers, it is possible to control polymer morphologies and to achieve property synergisms. Selected examples are presented to illustrate basic concepts and recent developments. Segmented reactive liquid rubbers, containing an immiscible silicone segment flanked by two miscible oligo(caprolactone) segments, are efficient epoxy toughening agents. In such nano-phase-separated silicone-modified IPNs impact strength is improved without sacrificing dimensional stability. Compatibilized blends of segmented phenolic polyurethane and nitrile liquid rubbers produce rubber blend microphases dispersed in epoxy prepregs which are used to bond aluminum sheets in structural laminates. Reactive blending technologies are developed to produce segmented polymers as blend compatibilizers during melt processing, e.g., of polypropylene/polyamide 6 blends. Incorporation of oligo(tetrafluoroethene) segments into various condensation polymers modifies thermal and mechanical properties as well as surface tension and gas permeabilities.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/apmc.1994.052230104
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  • 4
    Digitale Medien
    Digitale Medien
    Density Functional Studies on Amino-Substituted Methane and Silane (1997)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 130 (1997), S. 1745-1749 
    Details
    ISSN: 0009-2940
    Schlagwort(e): Density functional calculations ; Tetra(amino)methane ; Tetra(amino)silane ; Transition states ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In all-electron density functional calculations on mono- and tetraaminosubstituted methane and silane the coordination around the nitrogen center is found, in complete agreement with experiment, to be less pyramidal in the silicon compounds. The calculated barrier to inversion at nitrogen is only 0.6 kcal/mol in silylamine, while in methylamine it is 5.5 kcal/mol. The larger flexibility is attributed to the greater ionic character of the Si-N bond compared to that of the C-N bond. In tetra(amino)methane, inversion of one amino group leads to a local minimum (calculated inversion barrier: 6.4 kcal/mol), while a corresponding structure (or barrier) does not exist for the silicon compound. Due to the steric influence of the amino groups, the barrier to rotation around the C-N bond is larger in the tetrasubstituted compound (6.4 kcal/mol compared to 2.3 kcal/mol in methylamine). While the average binding energy of the amino groups is similar in both tetra(amino)compounds, the binding energy of the fourth ligand is about 25% larger in the silicon compound for both homolytic and heterolytic bond cleavage. This difference arises from the relative stabilization of the tri(amino)-methyl species, due to some n contribution to the C-N bond.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/cber.19971301207
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  • 5
    Digitale Medien
    Digitale Medien
    Low temperature modification of polymers by triazolinediones. Electrophilic substitution of poly(oxy-2,6-dimethyl-1,4-phenylene)Dedicated to Prof. H. Sinn on the occasion of his 60th birthday (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 1433-1443 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Poly(oxy-2,6-dimethyl-1,4-phenylene) (PPE, 8) is reacted with substituted 1,2,4-triazoline-3,5-diones 1 to give the partially substituted poly[oxy-2,6-dimethyl-3-(1,2,4-triazoline-3,5-dione-1-yl)-1,4-phenylene]9. The reaction occurs via electrophilic substitution of the electron-rich PPE with the highly electron deficient triazolinediones 1. For low degrees of substitution, the reaction readily occurs at room temperature. The inherent viscosity decreases with increasing substitution. The results are compared to similarly substituted polybutadiene. The glass transition temperature of the substituted PPE's decreases with the content of triazoline groups, a result which is interpreted by a distortion of the packing in glassy PPE.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1989.021900623
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  • 6
    Digitale Medien
    Digitale Medien
    Activity of Peroxo and Hydroperoxo Complexes of TiIV in Olefin Epoxidation: A Density Functional Model Study of Energetics and Mechanism (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2135-2145 
    Details
    ISSN: 1434-1948
    Schlagwort(e): Density functional calculations ; Epoxidation ; Peroxo complexes ; Titanium ; Transition states ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Epoxidation of olefins by TiIV peroxo and hydroperoxo (alkylperoxo) complexes was investigated using a hybrid DFT method (B3LYP). Reaction energies and activation barriers for direct oxygen transfer to ethylene as a model olefin were computed for various model complexes to compare the epoxidation activity of Ti(η2-O2) and TiOOR (R = H, CH3) moieties. The activity of complexes with a Ti(O2) peroxo group is shown to be essentially quenched when the coordination sphere of the complex is saturated by strongly basic (σ-donor) ligands. In contrast, the activity of a TiOOH functional group depends only weakly on the saturation of the coordination sphere of the Ti center. Substitution of methyl for hydrogen in a TiOOH group is found to slightly increase the activation barrier of epoxidation. The computational results give preference to reaction paths that involve TiOOR species. The factors governing the activity of Ti(O2) and TiOOR groups, in particular the effects of donor ligands, are discussed on the basis of a molecular orbital analysis.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    The role of compatibilizers and elastomeric interlayers in glass-bead-reinforced poly(propylene) (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 15 (1994), S. 691-696 
    Details
    ISSN: 1022-1336
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/marc.1994.030150905
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  • 8
    Digitale Medien
    Digitale Medien
    Mechanical and morphological properties of elastomer-modified polypropylene/polyamide-6 blends (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 56 (1995), S. 1599-1605 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Polypropylene/polyamide-6 (70:30) blends, containing dispersed discrete polyamide-6 microphases as matrix reinforcement, represent attractive materials for engineering applications. In order to enhance impact resistance, ethene/propene (EPM) was incorporated as a second separately dispersed microphase using reactive blending technology. Blend morphologies were controlled by adding maleic-anhydride-grafted-polypropylene (PP-g-MA) as compatibilizer during melt processing, thus enhancing dispersion and interfacial adhesion of the polyamide-6 phase. With PP-g-MA volume fractions increasing from 2.5 to 10 vol %, much finer dispersions of discrete polyamide-6 with average domain sizes decreasing from 8 to 0.8 μm were obtained. When polyamide-6 and ethene/propene (EPM)-rubber are dispersed simultaneously in the polypropylene matrix, impact resistance was improved. The influence of PP-g-MA volume fraction and blend morphologies on mechanical properties such as Young's modulus, yield stress, notched Charpy impact resistance was investigated. The ternary polypropylene/polyamide-6/EPM blend properties were compared with those of binary polypropylene blends containing the equivalent volume fraction of EPM. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1995.070561210
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  • 9
    Digitale Medien
    Digitale Medien
    Reactive blending of polypropylene/polyamide-6 in the presence of tailor-made succinic anhydride-terminated oligopropene compatibilizersDedicated to honor the 70th birthday of Professor Dr. Dr. h.c. H.-J. Cantow. (1993)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 4 (1993), S. 465-474 
    Details
    ISSN: 1042-7147
    Schlagwort(e): Polypropylene ; Polyamide ; Blend ; Compatibilizer ; Ziegler-Natta catalysts ; Metallocene ; Maleic anhydride ; Graft copolymer ; Block copolymer ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Various anhydride-terminated isotactic and atactic oligopropenes of number average molecular weights ranging between 1,000 and 10,000 g/mole, prepared by maleinating vinylidene-terminated propene oligomers obtained with isospecific and nonstereospecific metallocene-based Ziegler-Natta catalysts, have been evaluated as blend compatibilizers of polypropylene/polyamide-6 (70 vol%/30 vol%) blends to study the role of blend compatibilizer molecular architecture. When added during processing, as shown by IR spectroscopic analysis, the anhydride-terminated oligopropenes react with the amine-terminated polyamide-6 to yield polypropylene-block-polyamide-6 in situ. Such block copolymers are efficient dispersing agents. While the polyamide dispersion in the polypropylene continuous phase is not affected by blend compatibilizer stereoregularities, both stiffness and yield stress as well as notched Charpy impact strength increase with increasing stereoregularities and molecular weights. With oligopropene molecular weights exceeding 1,150 g/mole, the average size of the dispersed polyamide microphases correlates with the volume fraction of the oligopropene-block-polyamide-6 blend compatibilizer and the dicarboxylic acid anhydride/amine molar ratio.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pat.1993.220040710
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  • 10
    Digitale Medien
    Digitale Medien
    Anisotropic dispersion polymerization of N-(4-aminobenzoyl)-caprolactam in polymer melts (1994)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 5 (1994), S. 282-286 
    Details
    ISSN: 1042-7147
    Schlagwort(e): Dispersion ; Microcomposite ; Polyamide ; Polyaramide ; Molecular composite ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: When N-(4-aminobenzoyl)-caprolactam (PAC) is injected into polymer melts, dispersions of anisotropic polyaramide particles with average diameters of 100-400 nm and aspect ratios of 5-10 are formed within few minutes. At 200°C PAC dispersion polymerization yields caprolactam and predominantly poly(p-phenylenebenzamide), whereas with increasing polymerization temperatures PAC ring-opening polymerization accounts for the incorporation of 6-aminocaproic acid units into the polyaramide backbone. Covalent bond formation between microparticle surfaces and functional groups of the matrix polymer provides excellent interfacial adhesion and stabilizes the anisotropic polyaramide microparticle dispersions. This in situ PAC dispersion polymerization during melt processing, producing polyaramide-whisker reinforced thermoplastics, represents a versatile route to organic microcomposites exhibiting improved stiffness and strength.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pat.1994.220050507
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