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  • Chemistry  (74)
  • 2015-2019  (4)
  • 1985-1989  (70)
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  • 11
    Electronic Resource
    Electronic Resource
    Trace analysis at clay-modified carbon paste electrodes (1989)
    Weinheim : Wiley-Blackwell
    Electroanalysis 1 (1989), S. 167-172 
    Details
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon paste electrodes modified with montmorillonite clay are used for the collection of iron(III) from dilute solutions followed by voltammetric quantification of the surface-bound cation. Open-circuit conditions are maintained during the ion exchange preconcentration. The surface is regenerated by a brief exposure to a sodium carbonate solution. For 20 preconcentration/measurement/regeneration cycles, the response could be reproduced with 4.8% relative standard deviation. Factors influencing the response, such as electrode composition, preconcentration time, measurement and „cleaning“ solutions, ionic strength, coexisting metals, iron concentration, and other variables, have been investigated. A detection limit of 0.2 mg/liter was estimated following 3 min preconcentration. The unusual mechanisms of ion exchange processes at clays should lead to a new class of modified electrodes for preconcentration/voltammetric measurements.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140010213
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  • 12
    Electronic Resource
    Electronic Resource
    Influence of the structure on the photodegradation of poly(vinyl chloride), 3.Part 2: cf.5. Dependance of the quantum yield of dehydrochlorination on the isotactic content (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 477-485 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photodehydrochlorination of four poly(vinyl chloride) (PVC) samples of different tacticities, as studied previously, was compared with that of a PVC sample after being modified to various degrees by nucleophilic substitution with sodium benzenethiolate (NaBT). In order to separate the influence of substituted structures from that of the chromophoric group grafted onto the polymer, a series of PVC mixtures with sec-butyl phenyl sulfide (BPT), of compositions similar to those of modified polymers was also studied. The evolution of HCl was found to be a linear function of the absorbed dose in all cases. The quantum yield of dehydrochlorination, ΦHCl, as obtained from the slopes, appeared to decrease with the isotactic content. The results suggest specific isotactic triads to be markedly reponsible for the photodehydrochlorination, which would account for a mechanism based on the occurrence of chlorines of low dissociation energy at such triads.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900304
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  • 13
    Electronic Resource
    Electronic Resource
    Stereospecific functionalization of poly(vinyl chloride)Dedicated to Prof. P. Rempp on the occasion of his 60th birthday (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 223-230 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The substitution reaction of PVC with sodium dimethyldithiocarbamate (NaDC) and sodium azide (NaN3) was performed in cyclohexanone and dimethylformamide at various temperatures. The degree of compositional heterogeneity was estimated and found to be important up to conversions of about 0,5%, but to vanish afterwards. The evolution of unreacted iso, hetero and syndiotactic triads was measured by 13C NMR spectroscopy. For conversions of at least up to 12%, the content of both the isotactic and heterotactic triads was found to decrease, relative to the syndiotactic ones, but at different relative rates depending on the nucleophile. From these results, together with the kinetic ones, it is concluded that the reaction proceeds by a stereoselective mechanism. The results are discussed on the basis of a hypothesis concerning the role of the local triad conformations in PVC that contain the TT isotactic diad conformation. The results enable the selective substitution of PVC with NaDC and NaN3, which may be used as a useful tool to prepare specific graft copolymers based on PVC.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900201
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  • 14
    Electronic Resource
    Electronic Resource
    Tacticity and dielectric relaxation around the glass transition of poly(vinyl chloride). A thermally stimulated depolarization currents (TSDC) study (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 893-905 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermally stimulated depolarization currents (TSDC) technique has been used to study molecular motions around the glass transition in three different samples of poly(vinyl chloride) (PVC) varying in the contents of isotactic triads. The α-relaxation mode associated with cooperative molecular motions taking part in glass transition appears to be strongly dependent on tacticity. A secondary relaxation mode α′, different from the β-relaxation, has been detected just below the α-relaxation and at temperatures depending on the content of isotactic triads. Above the glass transition temperature the TSDC curves show a ρ-peak corresponding to the motion of free charges in the material. This process does not seem to be affected by tacticity. The results suggest that specific conformations of isotactic triads play an important role in the motion of chain segments in the polymer.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900422
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  • 15
    Electronic Resource
    Electronic Resource
    Properties of polyacetylene obtained with (η-Cp)2Ti(PMe3)2 (1989)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 1309-1317 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acetylene was polymerized by (η-Cp)2Ti(PMe3)2 at room temperature to give predominantly trans-polyacetylene. All properties are within the ranges reported for polyacetylene produced with Ti(OBu)4/AlEt3 as catalyst.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1989.021900611
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  • 16
    Electronic Resource
    Electronic Resource
    Dependence of glass-transition temperature Tg on tacticity of poly(vinyl chloride). A preliminary study by differential scanning calorimetry (1988)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 189 (1988), S. 567-572 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The glass-transition temperature, Tg, of poly(vinyl chloride) (PVC) has been found to depend linearly on both the overall isotactic triad content and a small fraction of isotactic triads. It was previously demonstrated, that the latter react with sodium benzenethiolate at temperatures as low as -30°C, probably because they adopt a definite local conformation. In general, it was believed before that the tacticity effect on Tg occurs only for disubstituted C—C-polymers, the results obtained in this work for PVC would suggest that specific conformations of isotactic triads can also enhance the motion of chain segments in the polymer.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1988.021890310
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  • 17
    Electronic Resource
    Electronic Resource
    Quantitative evaluation of soluble polymeric photosensitizers, 4Parts 1-3: cf.5-7. Trans-cis isomerization of stilbene photosensitized by polymerbound o- and p-benzyloxybenzaldehyde (1987)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 188 (1987), S. 1703-1711 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The grafting of o- and p-benzyloxybenzaldehyde onto linear chloromethylated polystyrene is described. The resulting soluble polymeric photosensitizers and their model compounds, o- and p-(p-isopropylbenzyloxy)benzaldehyde, were tested as triplet energy donors against trans-stilbene in benzene solution. Irradiation of the ortho-compounds gives rise to a transformation which has been tentatively attributed to an intramolecular photocyclization. Stern-Volmer constants for the photostable para-compounds were determined. Results for both types of compounds show that the sensitizer efficiency diminishes when it is bound to the polymer.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1987.021880717
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  • 18
    Electronic Resource
    Electronic Resource
    Dissociation constant of poly(ethylene oxide) macroion pairs in nitrobenzene (1986)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 187 (1986), S. 1367-1370 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The great stability of the cationic polymerization system, ethylene oxide/nitrobenzene, from an electrochemical point of view, was investigatd as well as the assumption that the stable salts of triphenylmethylium and the macroion pair have the same dissociation constant. The value was determined to be 9,4 · 10-3 mol · 1-1 at 293 K in nitrobenzene.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1986.021870605
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  • 19
    Electronic Resource
    Electronic Resource
    Some spectral and thermal contributions to the curing of new epoxy compounds with aromatic diamines (1986)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 187 (1986), S. 1907-1914 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The curing reaction of the new bis(2,3-epoxypropyl) 4,4′-carbonyldi-ω-phthalimidoalkanoates 1a-c was studied with several aromatic diamines 2a-c as curing agents. The process was followed by means of spectrophotometric techniques. The influence of the nature of the curing agent on the reaction rate was examined. The adduct formation yielding first chain extension, is the first step of the reaction, followed by crosslinking, once the gel point has been reached. The products obtained were found to be rather thermostable.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1986.021870810
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  • 20
    Electronic Resource
    Electronic Resource
    Water-insoluble dextrans by grafting, 3Part 2: cf.2.. Reaction of dextran with butyl isocyanate. Chemical hydrolysis (1987)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 188 (1987), S. 2831-2838 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The modification reaction of dextran with butyl isocyanate using 1,4-diaza[2.2.2]bicyclooctane as catalyst was studied. The structure of the resulting polymers was determined by means of IR, 1H and 13C NMR spectroscopy as well as by chemical analysis. A linear dependence of the reaction rate on the concentrations of polymer, butyl isocyanate and catalyst was found. The activation energy was found to be 38,5 kJ/mol (9,2 kcal/mol). The homogeneous hydrolysis in alkaline medium was found to be first order with respect to both the base and the butyl urethane concentrations. The activation energy, obtained for the base catalyzed homogeneous hydrolysis, was 83,7 kJ/mol (20,0 kcal/mol). The heterogeneous hydrolysis of a water insoluble modified dextran (degree of substitution = 0,72) showed that no hydrolysis takes place under the applied conditions.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1987.021881205
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