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  • Polymer and Materials Science  (2)
  • melting transition  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Analysis of a symmetric neopolyol ester (1996)
    Springer
    Journal of thermal analysis and calorimetry 46 (1996), S. 1093-1111 
    Details
    ISSN: 1572-8943
    Keywords: conformational disorder ; crystal ; DSC ; glass ; glass transition ; heat capacity ; melting transition ; tetra[methyleneoxycarbonyl (2,4,4-trimethyl) pentyl] methane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Quantitative thermal analysis was carried out for tetra[methyleneoxycarbonyl(2,4,4-trimethyl)pentyl]methane. The ester has a glass transition temperature of 219 K and a melting temperature of 304 K. The heat of fusion is 51.3 kJ mol−1, and the increase in heat capacity at the glass transition is 250 J K−1 mol−1. The measured and calculated heat capacities of the solid and liquid states from 130 to 420 K are reported and a discussion of the glass and melting transitions is presented. The computation of the heat capacity made use of the Advanced Thermal Analysis System, ATHAS, using an approximate group-vibration spectrum and a Tarasov treatment of the skeletal vibrations. The experimental and calculated heat capacities of the solid ester were compared over the whole temperature range to detect changes in order and the presence of large-amplitude motion. An addition scheme for heat capacities of this and related esters was developed and used for the extrapolation of the heat capacity of the liquid state for this ester. The liquid heat capacity for the title ester is well represented by 691.1+1.668T [J K−1 mol−1]. A deficit in the entropy and enthalpy of fusion was observed relative to values estimated from empirical addition schemes, but no gradual disordering was noted outside the transition region. The final interpretation of this deficit of conformational entropy needs structure and mobility analysis by solid state13C NMR and X-ray diffraction. These analyses are reported in part II of this investigation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01983623
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of a symmetric neopolyol ester (1996)
    Springer
    Journal of thermal analysis and calorimetry 46 (1996), S. 1113-1132 
    Details
    ISSN: 1572-8943
    Keywords: chiral molecule ; conformational disorder and motion ; crystal ; DSC ; heat capacity ; γ-gauche effect ; glass ; glass transition ; melting transition ; molecular mechanics computations ; tetra[methyleneoxycarbonyl (2,4,4-trimethyl) pentyl] methane ; solid state13C NMR ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The symmetric neopolyol ester tetra[methyleneoxycarbonyl(2,4,4-trirnethyl)pentyl]methane (MOCPM) has been studied by variable-temperature solid-state13C NMR and X-ray powder diffraction and compared to molecular mechanics calculations of the molecular structure. Between melting and glass transition temperatures the material is semicrystalline, consisting of two conformationally and motionally distinguishable phases. The more mobile phase is liquid-like and is, thus attributed to an amorphous phase (≈16%). The branches of the molecules in the crystal exhibit two conformationally distinguishable behaviors. In one, the branches are well ordered (≈56%), in the other, the branches are conformationally disordered (≈28%). Different branches of the same molecule may show different conformational order. This unique character of the rigid phase is the reason for the deficit of the entropy of fusion observed earlier by DSC. In the melt, solid state NMR can identify two bonds that are rotationally immobile, even though the molecules as a whole have liquid-like mobility. This partial rigidity of the branches accounts quantitatively for the observed increase in heat capacity at the glass transition. The reason for this unique behavior of MOCPM, a small molecule, is the existence of one chiral centers in each of the four arms of the molecule. A statistical model assuming that at least two of the chiral centers must fit into the order of the crystal can explain the crystallization behavior and would require 12.5% amorphous phase, 28.1% conformational disorder, and 59.4% crystallinity, close to the observed maximum perfection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01983624
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  • 3
    Electronic Resource
    Electronic Resource
    Heat capacity of poly(trimethylene terephthalate) (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2499-2511 
    Details
    ISSN: 0887-6266
    Keywords: heat capacity ; poly(trimethylene terephthalate) ; entropy ; enthalpy ; free enthalpy ; heats of transition ; glass transition ; melting ; crystallinity ; rigid-amorphous fraction ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The heat capacity of poly(trimethylene terephthalate) (PTT) has been measured using adiabatic calorimetry, standard differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC). The heat capacities of the solid and liquid states of semicrystalline PTT are reported from 5 to 570 K. The semicrystalline PTT has a glass transition temperature of 331 K. Between 340 and 480 K, PTT can show exothermic ordering depending on the prior degree of crystallization. The melting endotherm of semicrystalline samples occurs between 480 and 505 K, with a typical onset temperature of 489 K (216°C). The heat of fusion of the semicrystalline samples is about 15 kJ mol-1. For 100% crystalline PTT the heat of fusion is estimated to be 30 ± 2 kJ mol-1. The heat capacity of solid PTT is linked to an approximate group vibrational spectrum and the Tarasov equation is used to estimate the heat capacity contribution due to skeletal vibrations (θ1 = 550.5 K and θ2 = θ3 = 51 K, Nskeletal = 19). The calculated and experimental heat capacities agree to better than ±3% between 5 and 300 K. The experimental heat capacities of liquid PTT can be expressed by: \documentclass{article}\pagestyle{empty}\begin{document}$ C^L_p(exp) $\end{document} = 211.6 + 0.434 T J K-1 mol-1 and compare to ±0.5% with estimates from the ATHAS data bank using contributions of other polymers with the same constituent groups. The glass transition temperature of the completely amorphous polymer is estimated to be 310-315 K with a ΔCp of about 94 J K-1 mol-1. Knowing Cp of the solid, liquid, and the transition parameters, the thermodynamic functions enthalpy, entropy, and Gibbs function were obtained. With these data one can compute for semicrystalline samples crystallinity changes with temperature, mobile amorphous fractions, and resolve the question of rigid-amorphous fractions.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2499-2511, 1998
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Model of double associates for sorption of binary gas mixtures on polymers (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 160 (1988), S. 107-115 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ein einfaches Modell von Doppelassoziaten wurde verwendet, um die Doppelschichtsorption von binären Gasgemischen an flexiblen linearen Polymerketten zu beschreiben. Die Isothermengleichung nach diesem Modell ist ein einfaches Produkt der isothermen Gleichung, die die Doppelschichtadsorption von binären Gasgemischen an einer homogenen festen Oberfläche beschreibt und einer Funktion, die die spezifischen Merkmale der Sorption an Polymeren widerspiegelt.
    Notes: A simple model of double associates is used to represent bilayer sorption of binary gas mixtures on a flexible linear chain of a polymer. The isotherm equation derived in terms of this model is a simple product of the isotherm equation describing bilayer adsorption of binary gas mixtures on a homogeneous solid surface and a function reflecting specific features of sorption on polymers.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051600108
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