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  • 1980-1984  (3)
  • Chemistry  (3)
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  • 1
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The crystallization of flexible-chain molecules of different degrees of coiling is considered. The nature of the phase transition during crystallization is discussed. The revision of established notions on phase transitions in polymers leads to the concept of crystalline topomorphism, i.e., the existence of two crystalline types with different modes of packing of macromolecules in the macroscopic crystal though they belong to the same lattice class: folded-chain crystal (FCC) and extended-chain crystal (ECC). Phase diagrams in coordinates of degree of coiling vs temperature are plotted. The values of molecular orientation and temperatures at which each of both mechanisms of crystallization takes place are evaluated. The mechanisms of ECC growth under equilibrium conditions and under conditions of molecular orientation are discussed. It is shown that the melting of ECC obtained by the process of orientational crystallization is a second order phase transition, being analogous to a crystal-nematic phase transition. At the same time the melting of FCC provides all the features of a first order transition.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 33 (1982), S. 483-485 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Kristallisation von Polypropylen im orientierten parakristallinen Zustand und der Übergang in den smektischen Zustand beim isometrischen Schmelzen der kristallisierten Proben wurden untersucht. Die Ergebnisse werden unter der Annahme struktureller Umwandlungen der makromolekularen Helices interpretiert, was ein lokales Schmelzen der Helices voraussetzt.
    Notes: The results of the study of polypropylene crystallization from the oriented paracrystalline state and the transition to the smectic state observed during isometric melting of the samples crystallized in this manner are interpreted from the viewpoint of structural transition in helical polypropylene macromolecules inevitably involving the local melting of helices.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 33 (1982), S. 427-428 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Existenz einer spezifischen metastabilen Phase erlaubt es, mehrstufige elektronenmikroskopische Untersuchungen der Bildung der übermolekularen Struktur bei der Kristallisation von Polypropylen im orientierten Zustand durch zuführen. Der Vergleich mit Elektronenbeugungsaufnahmen liefert einen direkten Beweis dafür, daß die Bildung von Struktureinheiten der übermolekularen Ordnung im kristallinen Polypropylen, d. h. der Fibrillen und Lamellen, während der Orientierung erfolgt und die Kristallisation diese Strukturen nur fixiert.
    Notes: The existence of the specific metastable phase made it possible to carry out multistage electron microscopic investigation of the supermolecular structure formation in the crystallization of polypropylene in the oriented state. Comparison with the data of electron diffraction yielded a direct evidence of the fact that the formation of structural units of the supermolecular organization of crystalline PP, i.e. fibrils and lamellae, occurs in the stage of orientation, and crystallization itself only fixes these structures.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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