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  • Polymer and Materials Science  (9)
  • General Chemistry  (6)
  • 1995-1999  (15)
  • 1
    Electronic Resource
    Electronic Resource
    Highly branched radial block copolymers via dendritic initiation of aliphatic polyesters (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2793-2798 
    Details
    ISSN: 0887-624X
    Keywords: highly branched radial block copolymers ; dendritic initiation ; alipatic polyesters ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Living ring opening polymerization of ε-caprolactone initiated from the numerous chain-end hydroxymethyl groups of the analogous dendrimeric and hyperbranched polyesters derived from 2,2-bis(hydroxymethyl) propionic acid is described. By controlling the size of the dendritic macromolecule and the molar ratio of ε-caprolactone, a variety of highly branched radial block copolymers are obtained. Comparison of the results obtained for the dendrimeric and hyperbranched initiators demonstrates that the reactivity of the chain-end hydroxymethyl groups in the dendrimer are significantly greater than in the isomeric hyperbranched case. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2793-2798, 1998
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    A versatile and efficient synthesis of alkoxyamine LFR initiators via manganese based asymmetric epoxidation catalysts (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2161-2167 
    Details
    ISSN: 0887-624X
    Keywords: alkoxyamine ; living free radical polymerizations ; asymmetric epoxidation ; Jacobsen's catalyst ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Intramolecular cyclization in hyperbranched polyesters (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 1627-1633 
    Details
    ISSN: 0887-624X
    Keywords: hyperbranched macromolecule ; polyester ; focal point groups ; intramolecular cyclization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of monomer structure and catalyst on the synthesis of hyperbranched polyesters based on 4,4-(4′-hydroxyphenyl)pentanoic acid has been examined. The nature of the ester group and the catalyst have a significant effect on the molecular weight of the hyperbranched polyester but do not effect the degree of branching for these materials. The fate of the single ester group at the focal point of these hyperbranched macromolecules is probed by the synthesis and polymerization of 13C labeled methyl 4,4-(4′-hydroxyphenyl)pentanoate. Comparison of the molecular weights determined by 1H- or 13C-NMR spectra with those determined by osmometry suggest that intramolecular cyclization does not occur to a significant extent in these systems. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1627-1633, 1997
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Correlation between glass transition temperature and chain structure for randomly crosslinked high polymers (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2247-2259 
    Details
    ISSN: 0887-6266
    Keywords: glass transition temperature ; polymer ; repeat unit ; correlation ; structure ; rotational degrees of freedom ; topology ; copolymerization ; crosslinking ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The empirical form for the dependence, Tg(n) ≅ Tg(∞)·(1 + α/n), of the glass transition temperature Tg on the average number n of repeat units between crosslinks, is generalized for randomly crosslinked high polymers. The new form, Tg(n) ≅ Tg(∞) · [1 + c/(n·Nrot)], is based on a correlation study of data for 77 samples of 10 different sets of resins. The fitting parameter α is resolved into composition-dependent Nrot and composition-independent c terms. Nrot summarizes the average number of rotational degrees of freedom per repeat unit, and is estimated in a straightforward manner from the structure and mol fraction of each repeat unit. The value of c is found from data analysis to be 5 ± 2. The results of this work are consistent with expectations based on the entropy theory of glasses, and provide improved understanding and predictive ability for the properties of crosslinked polymers. © 1996 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    “Living” free radical polymerization of macromonomers: Preparation of well defined graft copolymers (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 155-166 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Well defined graft copolymers have been synthesized by a nitroxide-mediated “living” free radical process using pre-formed macromonomers. Analysis of the graft systems revealed that the macromonomer was efficiently incorporated into the polymeric backbone to give block copolymers of controlled molecular weight and narrow polydispersities. An added benefit of the “living” free radical process is that macromonomers, such as polylactide or polycaprolactone, which contain reactive functional groups can be used to form novel graft systems using this approach. Functionalized monomers or polymeric initiators were also used in the copolymerization mixture to give graft systems with a variety of functional groups attached to the backbone.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021980112
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  • 6
    Electronic Resource
    Electronic Resource
    Macromolecular engineering via ‘living’ free radical polymerizations (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 923-935 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The use of nitroxide-mediated ‘living’ free radical procedures as a synthetic tool for obtaining polymers with well defined and complex macromolecular architectures is discussed. The preparation of linear homo, block, and random co-polymers by ‘living’ free radical procedures have been demonstrated for a variety of systems and results in a significant increase in control over the macromolecular structure when compared to traditional free radical polymerization. The factors which affect the success of this novel synthetic approach will be reviewed and the advantages of ‘living’ free radical polymerization over other living polymerization techniques discussed. The synthesis and chemical stability of a wide range of unimolecular alkoxyamine initiators will also be demonstrated and their use in the preparation of complex macromolecular architectures such as hyperbranched polymers and hybrid dendritic-linear polymers illustrated.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Electron-stimulated desorption total cross-section determination for digermane on Si(100) (1998)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 105-108 
    Details
    ISSN: 0142-2421
    Keywords: ESD ; Si(100) ; electron-stimulated desorption ; silicon ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: We have studied digermane-covered Si(100) using electron-stimulated desorption (ESD). Estimates are presented for the total H(a) ESD removal cross-section for digermane-exposed Si(100) substrates at 85 K using electrons incident at 150 eV energy. It is found that electron-enhanced deposition of Ge occurs only when physisorbed digermane is present. Auger electron spectroscopy provided the means for determining the relative amounts of germanium adsorbed on the Si(100) surface following digermane exposures, electron irradiation and surface reconstruction. It is found that two coverage regimes are important: initial dosing of digermane on Si(100) at 85 K results in overlayers consisting of both physisorbed digermane and chemisorbed GeHx(a) (x=1, 2 or 3) species; and short anneals to 200 K following exposure of the Si(100) surface at 85 K lead to the presence of only chemisorbed GeHx(a). The two coverage regimes exhibit different ESD behavior. Two kinetic energy distribution (KED) peaks are seen when physisorbed digermane is present, and only one when it is absent. The ESD signal decay curves obtained from the two surfaces are also different: the presence of physisorbed digermane results in a two-component exponential signal decay; the absence of the physisorbed species results in a single-exponential decay. The total H removal cross-section from the physisorbed digermane overlayer was determined to be σ∽1.4×10-15 cm2, while that from Si(100) with only adsorbed GeHx present was found to be σ∽2.6×10-16 cm2. Our results suggest that adsorbed GeHx(a) species remain intact on the surface even when the Si(100) substrate is annealed to 200 K, indicating that hydrogen migration from surface GeHx(a) to Si surface sites does not occur at 200 K. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Initial adsorption of trimethylsilane on Ge(100) surfaces (1998)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 113-120 
    Details
    ISSN: 0142-2421
    Keywords: XPS ; x-ray photoelectron spectroscopy ; Ge ; adsorption ; trimethylsilane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Trimethylsilane (TMSiH) was adsorbed onto a Ge(100) surface at a temperature of -150±3°C and x-ray photoelectron spectroscopy (XPS) was used to study the resulting surface species as functions of the TMSiH exposure in Langmuir (L). The core-level C 1s, Si 2p and Ge 3d photoelectrons were monitored after each dosing. It was observed that the C-C bonds are the dominant species formed at the low doses of TMSiH. The second abundant species at the low coverage is the C-Ge bond. This indicated dissociative adsorption of TMSiH molecules onto a clean Ge(100) surface, which is similar to the adsorption of TMSiH molecules onto an Si(100) surface. As the dose increases, the Si-C species gradually increase due to physisorbed TMSiH on top of the C-C- and C-Ge-covered surface. This study clearly reveals the growth processes of TMSiH on a Ge(100) surface. The electronegativities of C, Si and Ge and the bond strengths of C-C, C-Si and C-Ge were invoked to discuss the initial formation of C-C and C-Ge on the Ge(100) surface. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of low-energy electron irradiation on submonolayer ammonia adsorbed on Pt(111) (1998)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 26 (1998), S. 97-104 
    Details
    ISSN: 0142-2421
    Keywords: ammonia ; Pt ; adsorption ; electron irradiation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The effects of electron impact on ammonia-covered Pt(111) have been studied using temperature-programmed desorption (TPD) and electron-stimulated desorption (ESD). For coverages below one monolayer, ammonia adsorbs on the surface in two distinct TPD states: the α-state is broad and desorbs over the temperature range 150-350 K, and the β-state appears as a sharper peak at 150 K. The β-state was seen to be damaged by electron-beam impact much more readily than the α-state, resulting in the formation of atomically adsorbed N on the surface. The mass 28 recombinative nitrogen desorption TPD peak appearing at 550 K exhibited second-order desorption kinetics, further confirming the presence of atomically adsorbed nitrogen. The ESD kinetic energy distributions (KEDs) were obtained for m/e=1 amu, which exhibited broad peaks generally. The H+ KEDs were analyzed using empirical curve fits, with the resulting conclusion that the H+ KEDs contain contributions from at least three different hydrogen-containing surface species. We believe that these three H+ KED peaks are due to ESD from adsorbed NH3, NH2 and H. The ESD cross-section for NH3 removal was measured in three different ways, all of which were found to be in general agreement, and which gave an averaged cross-section value of Qtot=4×10-17 cm2. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Kontrolle der Molekülarchitektur in lebenden radikalischen Polymerisationen: Herstellung von Stern- und PfropfpolymerenDiese Arbeit wurde vom National Institute of Standards and Technology durch den ATP-Vertrag Nr. 70 NANB-3H-365 gefördert. (1995)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 107 (1995), S. 1623-1627 
    Details
    ISSN: 0044-8249
    Keywords: Polymere ; Pfropfpolymere ; Radikalische Polymerisation ; Sternpolymere ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19951071332
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