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  • 1
    Electronic Resource
    Electronic Resource
    Conformational studies of bacterial polysaccharides. II. Optical activity of some bacterial capsular polysaccharidesPart I, see Ref. 29. (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 731-748 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optical activity of the Klebsiella capsular polysaccharides of serotypes K1, K5, K6, K8, K11, K56, and K57 has been studied in aqueous solution. Measurements of ORD in the range 185-450 nm reveal anomalous ORD with Cotton effects near λ0 = 195nm. The results are evaluated quantitatively according to hte Moffitt-Yang and the Drude equations. Straight lines are obtained in the Moffitt-Yang plots, while the corresponding Drude plots yield bent curves. The b0 values, calculated from the slope of the stright lines in the Moffitt-Yang plot, range from 90 to 270 and suggest a helical superstructure for the capsular polysaccyharides. Positive b0 values have been found for K1, K5, and K6 and negative b0 values for K8, k11, K56, ad K57. Circular dichrosim has been mesured, but the CD curves are found to be truncated at the lower-wavelength end due to the 185-nm limit of the spectrometer used. Measurements of the temperature dependence of the specific optical rotation [α] reveal in all cases cooperative order-disorder transitions at temperatures, Tm, fro m298 to 323°K. The van′t Hoff enthalpies derived from the width of the transition curves are found to be similar in value to those of polypeptieds in aqueous solution. The K8 polysaccharide shows a two-step transition. The results are discussed in relation to the known primary structure and x-ray data from oriented and partially crystalline films. A model is suggested for the two-step transition in the K8 polysaccharide.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1978.360170314
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  • 2
    Electronic Resource
    Electronic Resource
    Poly-α-ester degradation studies. II. Thermal degradation of poly(isopropylidene carboxylate) (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 11 (1973), S. 1079-1093 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal degradation of poly(isopropylidene carboxylate) has been studied over the temperature range 200-800°C by using the kinetic and analytical techniques described in Part I of this series. Over a wide range of temperature, tetramethyl glycollide, acetone, carbon monoxide, and, to a lesser extent, methacrylic acid are observed when the products are rapidly swept away from the reaction zone. As decomposition temperature is increased, tetramethyl glycollide takes on the role of an intermediate, the more stable products carbon monoxide and acetone being formed from it. At the highest temperature examined, carbon monoxide begins to predominate, and its formation is accompanied by formation of small amounts of a carbonaceous residue. When the reaction products are allowed to remain in the reaction zone, which is possible at the lower end of the temperature range, methacrylic acid becomes the major product. This is interpreted as a dual decomposition route, involving the tetramethyl glycollide intermediate. Kinetic studies have shown that the decomposition is a first-order process and that the first-order rate constant k is related to temperature (T) by the expression: \documentclass{article}\pagestyle{empty}\begin{document}$$ k = 4.1 \times 10^7 e^{{{ - 27,200} \mathord{\left/ {\vphantom {{ - 27,200} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}} {\rm sec}^{ - {\rm 1}} $$\end{document} The results are interpreted in terms of an intramolecular ester interchange process involving tetramethyl glycollide as the primary decomposition product.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.170110514
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  • 3
    Electronic Resource
    Electronic Resource
    Poly α-ester degradation studies. V. Thermal degradation of polyglycollide (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 11 (1973), S. 2045-2056 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal degradation of polyglycollide [poly(methylene carboxylate)] has been studied over the temperature range 250-400°C by using the combined kinetic and analytical technique previously described. The results obtained from thermogravimetry and product analysis were in many ways similar to those from previous work involving higher poly-α-esters. Thus the reaction was predominantly first-order and the major degradation product was glycollide monomer. This confirms the observations of Carothers and is best interpreted in terms of an intramolecular ester interchange process. Kinetic studies have shown that the first-order rate constant k is related to temperature T by the expression: \documentclass{article}\pagestyle{empty}\begin{document}$$ k = 2.1 \times 10^8 e^{ - 32,{{600} \mathord{\left/ {\vphantom {{600} {RT}}} \right. \kern-\nulldelimiterspace} {RT}}{\rm sec}^{ - {\rm 1}} } $$\end{document} The results from gas evolution analysis showed consistent and marked deviation from first-order behavior. This is interpreted in terms of the greater sensitivity of this technique to traces of acidic degradation products. Solution viscometry was used to demonstrate the effect of degradation conditions on molecular weight change in both thermogravimetric and gas evolution techniques.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.170110823
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  • 4
    Electronic Resource
    Electronic Resource
    Poly α-ester degradation studies. IV. Rheological studies of polymer degradation (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 11 (1973), S. 2031-2043 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Farol-Weissenberg rheogoniometer has been used to follow molecular weight changes during the degradation of certain poly-α-esters in the melt state. By observing the change in melt viscosity at low shear rates it had been shown that the decomposition of the poly(isopropylidene carboxylate) is substantially first-order with respect to the molecular weight of the residual polymer. The derived kinetic parameters are in good agreement with those previously obtained by other techniques. This provides a substantial piece of supporting evidence for the view that degradation takes place predominantly by intramolecular ester interchange involving the formation of 1,1,4,4,-tetramethylglycollide. The introduction of β-chlorine atoms into the polymer structure leads to a more complex degradation pattern. Thus the presence of a single β chlorine atom per repeat unit, as in poly(3-chloro-2-methyl-2-hydroxypropionic acid) leads to a substantially similar dependence on molecular weight with the added complication of progressive crosslinking which becomes more apparent in later stages of the reaction. This crosslinking reaction plays an increasingly important part as the extent of chlorination of the polymer is increased. In addition, the presence of chlorine leads to an increased sensitivity of the degradation reaction to the presence of oxygen.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.170110822
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  • 5
    Electronic Resource
    Electronic Resource
    Poly-α-ester degradation studies. III. Effect of β-chlorination on polymer degradation (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 11 (1973), S. 2343-2355 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal degradation of two β-chlorinated versions of poly(isopropylidene carboxylate) has been studied by the combined thermogravimetric and gas evolution techniques described previously. Poly(3-chloro-2-methyl-2-hydroxypropionic acid) was found to decompose by a predominantly first-order process which was characterized by kinetic parameters similar to those obtained for poly(isopropylidene carboxylate). These are interpreted in terms of an intramolecular ester-exchange process. As the reaction proceeds intermolecular elimination of hydrogen chloride leads to crosslinking and ultimately to the formation of a carbonaceous char. This process is much more marked in the randomly β-chlorinated analog of poly(isopropylidene carboxylate). With this polymer, drastic deviation from first-order behavior is observed in thermogravimetric results, even in the early stages of reaction. Gas evolution analysis, being more influenced by degradation fragments having an appreciable vapor pressure, yields reasonable first-order data and indicates that the intramolecular interchange mechanism is still an important process. In general, the introduction of β-chlorine atoms is seen to reduce the rate of thermal decomposition of poly-α-esters.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.170110923
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  • 6
    Electronic Resource
    Electronic Resource
    Poly-α-ester degradation studies. I. Introduction: Design and construction of equipment (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 11 (1973), S. 1069-1077 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The various types of polyester degradation known to occur at elevated temperature are briefly summarized with particular reference to features of potential diagnostic value. Although little is known of poly-α-ester degradation in particular, examination of work on other linear polyesters indicates the spectrum of analytical and kinetic information that will be needed to characterize the degradation of poly-α-esters of various structures. On the basis of this review, an apparatus has been designed which enables kinetic information to be simultaneously obtained by thermogravimetry, gas evolution analysis, and rheological studies of the residual polymer melt. In addition a gas sampling procedure enables twin-column gas-liquid chromatographic analysis to be carried out on the degradation products. Samples of the chromatographically separated degradation products are collected in a microcollector cell for infrared and mass spectrometric analysis. Other refinements include in-line filament and Curie-point pyrolysis techniques.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.170110513
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  • 7
    Electronic Resource
    Electronic Resource
    Poly-α-ester degradation studies. VI. Thermal degradation of poly(3-pentylidene carboxylate) (1980)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 18 (1980), S. 123-146 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal degradation of poly(3-pentylidene carboxylate) has been studied kinetically over the temperature range 200-300°C using thermogravimetry, gas evolution analysis, and rheogoniometry together with isolation and analysis of the reaction products. The observed behavior is completely different from that previously reported for poly(isopropylidene carboxylate) and poly(methylene carboxylate). Whereas in the latter cases the decomposition occurs by a first-order intramolecular ester interchange process characterized by an activation energy in the region of 27 kcal mole-1, poly(3-pentylidene carboxylate) decomposition occurs by random chain scission superimposed on a first-order hydrogen abstraction process. The activation energy associated with this decomposition reaction is in the region of 47 kcal mole-1, and the major degradation products are cis- and trans-2-ethyl crotonic acid.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1980.170180113
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  • 8
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    Altitudinal dependence of meteor radio afterglows measured via optical counterparts (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2016-08-26
    Description: Utilizing the all-sky imaging capabilities of the LWA1 radio telescope along with a host of all-sky optical cameras, we have now observed 44 optical meteor counterparts to radio afterglows. Combining these observations we have determined the geographic positions of all 44 afterglows. Comparing the number of radio detections as a function of altitude above sea level to the number of expected bright meteors we find a strong altitudinal dependence characterized by a cutoff below ∼ 90 km, below which no radio emission occurs, despite the fact that many of the observed optical meteors penetrated well below this altitude. This cutoff suggests that wave damping from electron collisions is an important factor for the evolution of radio afterglows, which agrees with the hypothesis that the emission is the result of electron plasma wave emission.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 9
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    F2-region atmospheric gravity waves due to high-power HF heating and subauroral polarization streams (2012)
    Wiley-Blackwell
    Details
    Publication Date: 2012-06-01
    Description: We report the first evidence of atmospheric gravity waves (AGWs) generated in the F2 region by high-power HF heating and subauroral polarization streams. Data come from the CHAMP and GRACE spacecraft overflying the High-frequency Active Auroral Research Program (HAARP) heating facility. These observations facilitate a new method of studying the ionosphere-thermosphere coupling in a controlled fashion by using various HF-heating regimes. They also reveal the subauroral F2 region to be a significant source of substorm AGWs, in addition to the well-known auroral E region.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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