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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of poly(aryl ether) dendrimers using an aryl carbonate and mixtures of metal carbonates and metal hydroxides (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 1781-1798 
    Details
    ISSN: 0887-624X
    Keywords: poly(aryl ether) dendrimers ; cascade polymers ; polyetherification reaction ; divergent approach ; activation/condensation sequence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four generations of poly(aryl ether) dendrimers containing aryl sulfide or aryl sulfone groups, and aryl fluoride terminal functionality, have been synthesized using the divergent initiator core method and bis(4-fluorophenyl) sulfone as the core precursor. The strategy is based on the divergent approach and an activation/condensation sequence that involves oxidation of the aryl sulfide group and the displacement of the activated halide moiety by a phenolate ion. The phenolate is easily generated in situ from an aryl carbonate. No reaction intermediates were detected when the condensation reaction was carried out utilizing a very active metal carbonate, such as cesium carbonate, in conjunction with magnesium hydroxide or calcium carbonate which removes some of the fluoride ions formed. The samples were characterized by HPLC, MALDI-TOF-MS, NMR, and SEC. Imperfections in some of the molecules of the dendrimers, formed by reaction of the core precusors with an impurity present in the phenol, were also identified by MALDI-TOF-MS. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1781-1798, 1997
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Preparation of hyperbranched macromolecules with aryl fluoride and phenol terminal functionalities using new monomers and Cs2CO3 or Mg(OH)2 as the condensation agent (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2015-2033 
    Details
    ISSN: 0887-624X
    Keywords: hyperbranched ; aryl ether sulfone ; polycondensation ; divergent approach ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New A2B monomers were synthesized for preparation of hyperbranched aryl ether sulfone macromolecules with aryl fluoride and phenol terminal functionalities. The macromolecules, which possess high thermal stability, were prepared using the divergent approach. A masked phenol with two aryl fluoride groups and a bisphenol with an aryl fluoride group were the monomers used to synthesize these polymers. In both cases, the aryl fluoride group is activated by a sulfone moiety. The synthetic method used for the preparation of the hyperbranched macromolecules gave a fast reaction and a high yield. These methods include, e.g., the use of Cs2CO3 and Mg(OH)2 to generate the phenolate ion in situ. Use of the latter results in the formation of insoluble magnesium fluoride. The best conditions for the reaction utilized the more active nucleophilic polycondensation agent, Cs2CO3, and an aryl carbonate as a masked phenol. NMR, SEC, and MALDI-TOF-MS were used to characterize the samples. MALDI-TOF-MS allowed us to identify the different oligomeric species present, and it also indicated that an internal cyclization competes with the polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2015-2033, 1997
    Additional Material: 9 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of surface fractality on the permeability of transparent gas barrier coatingsThis work was financially supported through BRITE EURAM II project BRE 2-CT92-0237 and the CSIC/CONICET cooperation program. The authors are indebted to CE.TE.V. (Italy) for providing the samples and performing the water vapor diffusivity measurements. They are also indebted to Otto Nielsen Emballage (Denmark) for performing the oxygen permeability measurements. (1997)
    Weinheim : Wiley-Blackwell
    Advanced Materials 9 (1997), S. 654-658 
    Details
    ISSN: 0935-9648
    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
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/adma.19970090815
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  • 4
    Electronic Resource
    Electronic Resource
    Deformation, scattering, and birefringence of flexible polymer chains under external forces or electric fields (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 689-697 
    Details
    ISSN: 0887-6266
    Keywords: tensile force ; electric field ; chain conformation ; birefringence ; scattering ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of a tensile stress or an electric field on the conformation of a flexible polymer chain has been studied by combining theory with numerical simulation. In the presence of such external agents, the macromolecule experiences the action of two opposite forces at the chain ends. Two models are considered: the Gaussian bead-and-spring chain, and the freely jointed chain with segments of fixed length. From simulated Brownian trajectories we calculate steady-state properties of the polymer under the continuing action of the external forces. Thus, we compute the chain deformation and expansion, measured by the square radius of gyration, and analyze the influence of the external force on low-angle scattering of radiation. The effect of the link orientation in the optical anisotropy or birefringence is also analyzed. From existing theories, we predict very simple relationships between expansion, low-angle scattering, and birefringence, valid for Gaussian chains of any length, and for long freely jointed chains. The simulation results confirm those relationships. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 689-697, 1997
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Polymorphism in an oligo(aryl ether ketone)Dedicated to Prof. Dr. F. J. Baltá Calleja on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 2089-2099 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1,3-Bis(4-phenoxybenzoyl)benzene (1) shows a single melting peak at T1 = 120°C when rapidly crystallized from a methanol/benzene mixture (10:1 v/v) (sample A) and a double melting peak at T1 = 120°C and T2 = 130°C when crystallized slowly (overnight) (sample B). Slow recrystallization of 1 using ethanol instead of methanol induces the formation of large single crystals which only show a single melting peak at T2 = 130°C (sample C). Analysis of powder X-ray diffractograms obtained for A, B and C samples clearly point out the coexistence of two crystalline phases in sample B: phase 1 (observed for sample A) and phase 2 (sample C). From optical microscopy and thermal (DSC) observations, it can be concluded that, upon heating, phase 1 melts at T1 and the molten material converts itself into phase 2 if some crystals of phase 2 are present. Single crystal structure determination of, both, phase 1 and 2 reveal conformational differences of the molecule in both phases which pack in an orthorhombic and a monoclinic unit cell, respectively.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021980707
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis of polymeric organic-inorganic hybrid materials. Partially deacetylated chitin-silica hybrid (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 18 (1997), S. 163-167 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This work reports the synthesis of a novel polymeric organic-inorganic hybrid. The inorganic component is a silica network obtained by controlled hydrolysis of tetraethyl orthosilicate via sol-gel process and the organic counterpart is partially deacetylated chitin (CHI). The resulting polymer hybrids were homogeneous transparent film forming glassy materials being compatible through a wide composition range. Simultaneous thermal analysis of a CHI/silica 1:1 mixture confirms the intermolecular complex formation between organic and inorganic polymers.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1997.030180214
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  • 7
    Electronic Resource
    Electronic Resource
    Branched poly(ethylene glycol) linkers (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 2489-2498 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Novel types of methoxy poly(ethylene glycol) (PEG) linkers (U-PEG linkers) have been synthesized. These PEG linkers are linear polymers that attach to bioactive agents via a functional group, derived from a 2° alcohol, located in the center of the polymer chain versus the traditional terminal attachment site. These new types of linkers can be prepared with different functional groups (e.g. active ester, succinimidyl carbonate, and carbazate) for selected point of attachment, including ethylene oxide oligomers to provide “stems” when steric factors need to be addressed. Conversion of p-nitrophenyl carbonates to the more desirable succinimidyl carbonates has also been accomplished by a novel nucleophilic displacement procedure. Modification of proteins with these reagents is easily accomplished and is illustrated by the conjugation of a U-PEG linker with L-asparaginase.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021980810
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of Photoetching on Porous Silicon Morphology (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 677-682 
    Details
    ISSN: 0142-2421
    Keywords: silicon ; light irradiation ; surface tension ; transmission electron microscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The morphological differences between porous silicon formed in the dark or under illumination have been studied by means of gravimetric measurements, transmission electron microscopy, infrared spectroscopy and cyclic voltammetry. Photoetching has been found to give rise to a complex surface structure, due to the presence of narrower outer silicon fibres, which suffer a more severe cracking process upon drying. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Characterization of the interfaces formed during the silicidation process of Ti films on Si at low and high temperatures (1997)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 25 (1997), S. 896-903 
    Details
    ISSN: 0142-2421
    Keywords: titanium silicide ; Schottky barrier ; silicidation ; rapid thermal annealing ; interface ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The silicidation process of titanium on silicon shows three distinct ranges depending on the treatment temperature. From 700°C up to 900°C, a stable and reproducible TiSi2 C54/Si structure is formed for all treatment conditions. At lower temperatures the silicidation process is not complete, and several silicide phases appear during the thermal treatment. On the other hand, the silicidation at high temperatures (T〉900°C) provokes changes in the TiSi2/Si structures. We have centred our interest in these two extreme ranges of temperature. The degree of silicidation has been established by Rutherford backscattering and grazing-incidence x-ray diffraction. It has been observed that TiSi and TiSi2 C54 are the only silicide phases present in the film at low temperatures. The distribution of phases has been determined by transmission electron microscopy. The high-resolution electron microscopy images indicate that the silicide/silicon interface is very flat, but the interface between the different phases of the silicide is not well defined. High-resolution electron microscopy and I-V measurements have been used to characterize the interface formed between the silicide and the silicon at high temperatures. At 1050°C the interface is flat in a scale of nanometres but it is rough in a scale micrometres. This roughening is not high enough to explain the decreasing of the Schottky barrier height. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
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