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  • 1
    Electronic Resource
    Electronic Resource
    Infrared spectroscopic studies on polyethylene, 1. The measurement of low levels of chain branching (1976)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 177 (1976), S. 437-448 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Probleme, die bei Anwendung der Kompensationsmethode auf IR-spektroskopische Bestimmungen von niedrigen Verzweigungsgraden in Polyäthylenen hoher Dichte auftreten, werden systematisch untersucht. Die erzielbare Genauigkeit wird bestimmt und es wird gezeigt, daß, wenn möglich, eine Korrektur für die Methyl-Endgruppen angewendet werden sollte. Diese ist bei einigen Polymertypen leicht möglich, bei anderen hingegen schwieriger. Als Kompensationskeil im Referenzstrahl des Spektrometers verwendet man besser Polymethylen als hochmolekulares Polyäthylen. Die äußerste Empfindlichkeit, die mit der manuellen Kompensationsmethode erreicht werden kann, liegt bei einem Methylzweig pro 2000 C-Atome. Wenn diese Methode jedoch ergänzt wird durch Computer-Kurvendämpfung und Computer Mittelung über zahlreiche Momentspektren (“C.A.T.”), kann noch eine deutliche Verbesserung im Signal-Rausch-Verhältnis erzielt werden. Damit wird es möglich noch Verzweigungsgrade bis herunter zu 0,1 Methylgruppen pro 1000 C-Atome zu messen.
    Notes: The problems encountered in the infrared spectroscopic estimation of the low levels of chain branching present in high density polyethylene, using the compensation method, are discussed systematically. The precision to be expected has been determined and it is shown that, if possible, a correction should be applied for methyl groups present at the chain ends. This is feasible with some types of polymer but more difficult with others. The compensating wedge in the reference beam of the spectrometer should be made of polymethylene rather than a high molecular weight polyethylene. The ultimate sensitivity of the manual compensation method is about one methyl branch per two thousand carbon atoms. However, when this is supplemented by computer smoothing and off-line computation of average transients (C.A.T.), a significant improvement is obtained in the signal to noise ratio, and branching levels down to 0,1 methyl groups per thousand carbon atoms are readily measured.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1976.021770212
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  • 2
    Electronic Resource
    Electronic Resource
    A study of methods for measuring the tacticity of poly(vinyl chloride) by proton magnetic resonance spectroscopy (1978)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 179 (1978), S. 2895-2912 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 60 MHz undecoupled α-, 90 MHz undecoupled β-, and 90 MHz decoupled α- and β-proton spectra were measured for seven poly(vinyl chloride) samples, four of these being commercial type polymers, the others were prepared at +75°C, +5°C and -30°C. The results were used to assess the preferred approach to the determination of tacticity. The reproducibility of the values from different solutions of a given polymer is significantly worse than that between a series of runs on a particular solution, showing that sampling errors are larger than those from instrumental sources. Although the 60 MHz spectra were found to be unsatisfactory when interpreted on a first order basis, curve fitting methods, which were similar to those used for the other types of spectra and involved the use of reasonable assumptions for chemical shifts and coupling constants, gave results of comparable precision to those from the two types of decoupled spectra and superior to those from the undecoupled 90 MHz spectra. The preferred approach is to combine the results from α- and β-proton spectra and to examine more than one solution of a given material. The applicability of Bernoullian propagation statistics was assumed in the majority of the curve fitting calculations; in the cases where this was not so the results were used to test this assumption and it has proved to be valid.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1978.021791209
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  • 3
    Electronic Resource
    Electronic Resource
    Infrared spectroscopic studies on polyethylene, 5Part 4: cf.1.. The measurement of chain branching on powder polyethylene specimens (1979)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 180 (1979), S. 975-987 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The scope and limitations of the potassium bromide disc technique for the infra-red determination of chain branching in small samples of polyethylene in powder form have been assessed. Many of the samples encountered have an average particle size, prior to grinding with potassium bromide, of about 100 μm and very satisfactory results have been obtained, but the presence of larger particles leads to poor quality discs and inferior results. The well established double beam technique proves suitable for removing the interfering methylene absorption and compensation with polymethylene in the form of a film rather than as a pressed disc is preferable. Difficulties were encountered in preparing branching standards in a uniform and fine powder form, to avoid variation of the absorption coefficient of the 1 378 cm-1 methyl band with particle size. Such powders are best obtained by precipitation from solution rather than by low temperature milling. Despite these problems chain branching measurements may be made with a precision of between 5 and 10% and an accuracy of about 15%.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1979.021800414
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  • 4
    Electronic Resource
    Electronic Resource
    Polyene sequence distribution in modified poly(vinyl chloride) after thermal degradation (1984)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 185 (1984), S. 1277-1284 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The products resulting from the reaction of PVC with sodium benzenethiolate were degraded to 0,3% at 180°C in the solid state and at 160°C in solution in trichlorobenzene. The polyene distribution of the polymers after degradation was studied by both UV-visible and resonance Raman spectroscopies, as a function of the degree of substitution. The results show that there are two types of behaviour: that of the PVC sample prior to the substitution reaction together with the samples modified up to a definite degree of substitution which depends on the starting isotactic content, and that of samples with higher degrees of substitution. The former group exhibits not only a steady improvement in thermal stability but also a preferential formation of polyenes of 7 - 9 double bonds whose concentration decreases with increasing degree of substitution. Conversely, for the second group of samples the thermal stability decreases with the degree of substitution and no specific absorption bands are observed. On the basis of earlier work on the selective substitution of the isotactic GTTG and heterotactic TTTG triads during the first stage of the reaction, the present results show that the bands at 393, 416, and 437 nm are related to specific polyenes which result from initiation by the above quoted conformations in PVC, a conclusion for which confirmatory evidence was obtained by resonance Raman spectroscopic examination of the samples. There is, therefore, clear evidence for the occurrence of two distinct degradation mechanisms, one involving initiation by the unstable triad conformations and the other via random initiation at stable and normal structures. To this may be added the initiation by defect structures, which have been extensively documented in the literature.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1984.021850701
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  • 5
    Electronic Resource
    Electronic Resource
    Formation of conjugated polyenes by chemical and thermal degradation of vinyl chloride copolymers and other vinyl polymers (1985)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 186 (1985), S. 715-723 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman and infrared spectroscopic studies on the chemical degradation products of two vinyl chloride/vinyl acetate copolymers and a vinyl chloride/vinyl acetate/vinyl alcohol terpolymer, obtained with the system potassium tert-butoxide/N,N-dimethylformamide, show that substantially complete dehydrochlorination occurs. Although the vinyl acetate groups are hydrolysed to the corresponding alcohol these latter largely remain intact and block the extension of the polyene sequences, whose lengths, measured by Raman spectroscopy, are in agreement with values calculated from the initial polymer composition. No degradation other than hydrolysis occurs with vinyl acetate and vinyl alcohol homopolymers or a vinyl alcohol/vinyl acetate copolymer. The thermal degradation of the copolymers containing vinyl chloride, and of two vinyl chloride homopolymers of differing syndiotacticity, at 153°C in N,N-dimethylformamide, gives both dehydrochlorination and elimination of the comonomer units, the latter reaction occurring at least as rapidly as the former. A crosslinked structure, in which there is some steric stabilisation and, hence, conjugated polyene sequence lengths up to about 40, is formed. A maximum sequence length of 8 is found in thermally degraded poly(vinyl acetate), but the conjugated polyenes are too short to be detected in degraded poly(vinyl alcohol) and the vinyl alcohol/vinyl acetate copolymer.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1985.021860405
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  • 6
    Electronic Resource
    Electronic Resource
    The chemical dehydrochlorination of poly(vinyl chloride), 2Part 1: cf.1. Studies on N,N-dimethylformamide solutions (1985)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 186 (1985), S. 707-714 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The chemical dehydrochlorination of poly(vinyl chloride) was studied in solution in N,N-dimethylformamide. By comparison with solutions in tetrahydrofuran, examined previously, the reaction was found to occur at a significantly enhanced rate for the four systems studied, a mass polymer of 55% syndiotacticity and a low temperature polymer of 63% syndiotacticity, dehydrochlorinated with potassium hydroxide or with potassium tert-butoxide. Furthermore, at dehydrochlorination levels up to about 60%, markedly longer polyene sequences are formed, the more so in the case of potassium tert-butoxide., where they reach values of at least 65, as assessed by Raman spectroscopy. For levels of 80%, and greater, there is a significant decrease in the sequence lengths, the result of cross-linking, which is facilitated by the substantial loss of the \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} ({\rm CHCl \hbox{---} CH}_{\rm 2} \rlap{--} )_n$\end{document} sequences that sterically protect the long polyenes in the les heavily dehydrochlorinated materials. Limited results are also presented for chemically dehydrochlorinated PVC prepared by the urea clathrate method; the insolubility of this polymer probably leads to degradation on the surface of the particles only.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1985.021860404
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  • 7
    Electronic Resource
    Electronic Resource
    Infrared spectroscopic studies on polyethylene, 6Part 5: cf. C. Baker, P. David, W. F. Maddams, Makromol. Chem. 180, 975 (1979).. Linear low density polymers (1985)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 186 (1985), S. 1665-1670 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The infrared spectra of five linear low density polyethylenes, containing methyl, ethyl, butyl, isobutyl and hexyl branches, respectively, were measured. Particular interest attaches to the region 800-1200 cm-1 where the spectra, although weak, show significant differences. The findings of an earlier study on the methyl rocking mode, in the vicinity of 900 cm-1, are confirmed and extended. In particular, no band was detected for the ethyl branched polymer and it must be an order of magnitude weaker than for methyl, butyl and hexyl branches. Conversely, it is displaced in frequency and is markedly stronger for isobutyl branches. The methyl wagging mode band is at about 1 150 cm-1 with the methyl branched polymer. It is relatively broad and probably consists of two overlapping components, specific for methyl branches in crystalline and amorphous regions. This mode is not of detectable intensity for ethyl, butyl and hexyl branches but, as with the rocking mode, it is anomalously strong for isobutyl branches.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1985.021860814
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  • 8
    Electronic Resource
    Electronic Resource
    A note on the quantitative estimation of chain branching in poly(vinyl chloride) (1973)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 165 (1973), S. 321-323 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1973.021650128
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  • 9
    Electronic Resource
    Electronic Resource
    Polyene sequence distribution in degraded poly(vinyl chloride) as a function of the tacticity (1979)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 180 (1979), S. 2937-2945 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Four fractions of poly(vinyl chloride) (PVC) having appreciably different tacticity distributions were prepared by selective extractions on samples polymerised at temperatures between +60 and -50°C. They were degraded thermally at 180°C in the solid state to conversions in the range 0,2 to 0,5% and in solution at 200°C to conversions in the range 1,6 to 5%. The polyene sequence distribution was investigated by ultra violet/visible (UV/VIS) and resonance Raman spectroscopy. The results show that the type of polyene sequence distribution depends markedly on the tacticity distribution of the polymer. Cross-linking reactions occur more readily as the syndiotacticity increases. The results are discussed and interpreted with reference to previous work relating degradation processes and tacticity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1979.021801215
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  • 10
    Electronic Resource
    Electronic Resource
    The measurement of the tacticity of poly(vinyl chloride) by 13C nuclear magnetic resonance spectroscopy (1983)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 184 (1983), S. 879-891 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Fourier transform 1H-decoupled 13C NMR spectra were obtained on seven poly(vinyl chloride), (PVC), samples in solution in o-dichlorobenzene. Four of the polymers were of the commercial type and the others were prepared by suspension polymerisation at +90°C, +5°C, and -30°C. Measurements of the spectra were used to assess the precision and accuracy with which information about the tacticity of PVC can be obtained from such spectra. The results show that the well-resolved α-carbon triad and β-carbon tetrad spectra obtained may be reliably analysed to give values of the probability of syndiotactic placement with a precision of about 0,005 for measurements on a single run on a single sample. The simplest and probably the most reliable method of measuring the areas under the peaks which correspond to specific triads ot tetrads is to use the spectrometer integrator, although results of slightly lower precision may be obtained by the use of a curve resolver. Consideration of possible systematic errors due to different T1 relaxation times, unequal nuclear Overhauser enhancement (NOE) factors, and incomplete dissolution of the polymer has shown that the only one of these which is possibly significant is that due to NOE, which is almost certainly less than 0,008, so that the absolute accuracies of the Pr values should be better than that. A more detailed study of the data shows that the polymers made at 5°C and -30°C are almost certainly non-Bernoullian and that firstoder Markov statistics can adequately describe the observed departures from Bernoullian statistics. These departures may have significant consequences for the physical properties of the polymers.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1983.021840421
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