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  • Polymers
  • Wiley-Blackwell  (6)
  • 1995-1999  (3)
  • 1960-1964  (3)
  • 1
    ISSN: 0570-0833
    Keywords: catalysis ; enantiomeric resolution ; imprinting ; molecular recognition ; polymers ; Imprinting ; Molecular recognition ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Can binding sites be produced in organic or inorganic polymers - similar to those in antibodies - which are able to recognize molecules and which may have catalytic action? In this article we review a method, analogous to a mechanism of antibody formation proposed earlier, by which in the presence of interacting monomers a cross-linked polymer is formed around a molecule that acts as a template. After removal of the template, an imprint containing functional groups capable of chemical interaction remains in the polymer. The shape of the imprint and the arrangement of the functional groups are complementary to the structure of the template. If chiral templates are used, the success of the imprinting process can be assessed by the ability of the polymer to resolve the racemate of the template molecule. Through optimization of the process has led to chromatographic separation factors of α = 4-8, and to base line separations. There is also great interest in the surface imprinting of solid materials and monolayers. In all cases, the structure of the polymeric matrix in the imprinted materials and the function of the binding groups are of crucial importance. The mechanisms of imprinting and molecular recognition of substrates are by now well understood. A large number of potential applications for this class materials are being intensively developed, for example in the chromatogrphic resolution of recemates, and as artificial antibodies, chemosensors, and selective catalysts. The use of similarly produced materials as enzyme models is also of great interest.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0570-0833
    Keywords: boron ; ceramics ; nitrides ; polymers ; silicon ; Boron ; Ceramics ; Nitrides ; Polymers ; Silicon ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Materials research is an interdisciplinary field in which engineers and physical scientists work together. Since the major binary oxides, nitrides, and carbides, which are currently used as high-performance ceramics, were discovered in the last century, the role of chemistry in the development of materials has become barely noticeable. This has changed only in the recent past as, for example, purity and defined morphology of starting powders were recognized as crucial parameters for enhancing the reliability of ceramic workpieces. While the application of chemical methods led to gradual-though significant-improvements, the true potential of chemistry lies rather in the exploitation of new chemical systems and the development of new preparative routes to already known materials. Such an approach is the preparation of ceramics from molecular or polymeric precursors. Herein we survey the most important contributions to those preparative routes starting from the pioneering work in the 1960s and the 1970s; a certain emphasis is placed on the concepts that we have applied to the preparation of multinary, nonoxide materials and amorphous inorganic networks. The name “amorphous high-performance ceramics” is in fact a contradiction in terms. Such materials are thermodynamically unstable with respect to the transformation or decomposition to crystalline phases, thus excluding their application in sensitive areas at high temperatures. However, the selection of element combinations for which the binding energies are derived from strong, local covalent bonds and which are therefore less dependent on a long-range crystalline order, can yield amorphous materials of remarkable thermal and mechanical durability. This is exemplified by novel quaternary ceramics in the Si/B/N/C system, for which an efficient synthesis, starting from raw materials suitable for industrial production, has been developed. For instance, a material of the composition SiBN3C remains amorphous up to 1900°C, which is unique, and, with respect to oxidation, is the most stable nonoxide ceramic known to date. Another advantage of this in several respects unsurpassed material is the simple way, in which the viscosity of the polymeric precursors can be adjusted to various methods of shaping. So far infiltrations and coatings have been realized. Most developed is the preparation of fibers, which in terms of their performance characteristics are significantly better than those currently available.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0570-0833
    Keywords: homogeneous catalysis ; industrial chemistry ; organometallic chemistry ; polymers ; reagents ; Homogeneous catalysis ; Industrial chemistry ; Organometallic compounds ; Polymers ; Reagents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homogeneous catalysis is the success story of organometallic chemistry. Otto Roelen's initial discovery of hydroformylation in 1938 not only entailed large-capacity production plants but was later followed by systematic research into the catalytic chemistry of the ever-growing class of organometallic compounds. Further developments in industrial chemistry towards clean, low-temperature, low-pressure, and economic processes - in feedstock or in the fine chemicals and polymer area - clearly depend on improved catalysts. Molecularly defined, tailor-made structures are the safest prerequisites for chemical selectivity; hence, organometallic compounds with their overwhelming variety of compositions and structures offer the most promising approach. Wilkinson's catalysts [HRh(CO){P(C6H5)3] and [ClRh{P(C6H5)}3}3] are outstanding examples. On the other hand, process technology has to be considered also (for example catalyst-product separation and hear-exchange problems). The following review attempts to critically assess the future trends and present demands in the applied area of orgnometallic catalysis-a “gentle art” that is far from being a mature field.
    Additional Material: 2 Ill.
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  • 4
    ISSN: 0570-0833
    Keywords: Tacticity ; Polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction course and kinetics of interfunctional reactions with polymers are determined by the microtacticity of the polymer chain. Among other things, this is shown by the hydrolysis of ester and amide polymers of different tacticities, and by ring-closure reactions (anhydride formation). The physical and physico-chemical properties are also governed by the tacticity.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0570-0833
    Keywords: Oligomers ; Pleionomers ; Polymers ; Fibers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The term “oligomer” is defined, and a survey of methods for the isolation and synthesis of cyclic and linear oligoesters, oligourethanes, oligo(acrylonitriles), and oligoamides is presented. The oligomers serve a valuable function as model substances for the investigation of many properties of the corresponding high polymers. This is shown using several examples (infrared spectroscopy, X-ray spectroscopy, viscosity).
    Additional Material: 1 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0570-0833
    Keywords: Heat resistance ; Fibers ; Polymers ; Materials science ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This survey is principally concerned with papers published since 1959 on hydrocarbon polymers, aliphatic poly(terephthalamide) fibers, poly(hydroxybenzoic acid) films, poly(oxadiazole) fibers, poly(benzimidazole) films, poly(phenyltriazole) films, poly(pyromellitimide) films, and fibers from cyclized poly(acrylonitrile). All these materials have extremely high melting points and satisfactory in-use characteristics at high temperatures.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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