Der Einfluß des Raumbedarfs der Kristallite auf die Entropie teilkristalliner Hochpolymerer

Zachmann, H. G.; Spellucci, Peter

doi:10.1007/bf01552512

Cited by 33 publications

(7 citation statements)

References 11 publications

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“…34 The rise in the low endotherm melting temperature with heating rate, observed after correction of thermal lag effects, is explained by superheating effects, as discussed by Wunderlich 35 and Zachmann. 36 Anticipat- ing conclusions drawn later in this paper but introduced earlier for random ethylene/R-olefin copolymers, 1,2 we associate the low endotherm with the melting of secondary crystals in a conformationally constrained environment. We suggest that, in the case of PEEK, this melting process results in the formation of a nonequilibrium amorphous fraction, which is characterized by a lower molar entropy than that of the metastable unconstrained melt at the same temperature.…”

Section: Two-step Crystallization Studiessupporting

confidence: 64%

“…One might be tempted to explain this behavior by a mechanism of fractionation during primary crystallization. 18,36 However, we refute this explanation since a similar multiple melting behavior is observed in narrow fractions of poly-(arylene ether ether ketone), 26 isotactic polystyrene, 45 and bisphenol A polycarbonate. 3 We now turn our attention to crystallization studies carried out below ca.…”

Section: Two-step Crystallization Studiesmentioning

confidence: 76%

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Influence of Structural and Topological Constraints on the Crystallization and Melting Behavior of Polymers. 2. Poly(arylene ether ether ketone)

et al. 2000

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The secondary crystallization and its influence on the glass transition are studied as a function of crystallization temperature and time by differential scanning calorimetry for PEEK. The multiple melting behavior resulting from isothermal annealing from the glass or crystallization from the melt is discussed in the context of models considering either a melting-recrystallization-remelting process or a bimodal population of primary and secondary crystals. The heating rate dependence of the multiple melting behavior indicates that reorganization of primary crystals occurs during heating for samples annealed from the glassy state but is insignificant for those crystallized from the melt. For either mode of crystallization, the high-and low-temperature endothermic regions are associated with the melting of primary and secondary crystals, respectively. Investigations of the low endotherm transition temperature and heat of fusion as a function of crystallization time and temperature lead to the following conclusions: the melting temperature of secondary crystals increases linearly with the logarithm of secondary crystallization time at a rate, B(T), increasing linearly with decreasing temperature; the Avrami exponent, which characterizes the initial stage of secondary crystallization, is constant below ca. 310 °C (n ) 1 /2) but increases gradually with temperature above 310 °C; the late stage of secondary crystallization is characterized by a linear increase in crystallinity with logarithm of time. Studies of the evolution of the glass transition after secondary crystallization indicate that the calorimetric Tg increases linearly with the logarithm of time at a rate, b(T), increasing with decreasing temperature. Finally, a qualitative model of polymer crystallization of semiflexible polymer chains is proposed. This model considers the effect of structural constraints (chain stiffness) on the nature of the amorphous phase after primary crystallization and the effect of topological constraints (pinning of amorphous chains) on the secondary crystallization behavior.

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Section: Two-step Crystallization Studiessupporting

confidence: 64%

Section: Two-step Crystallization Studiesmentioning

confidence: 76%

Influence of Structural and Topological Constraints on the Crystallization and Melting Behavior of Polymers. 2. Poly(arylene ether ether ketone)

et al. 2000

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“…lamellae in accordance with their thickness and evidently, to a negligible extent, to a changing entropy of melting. Up to now several authors had thought this entropy to be the more important reason [2][3][4][5][6][7][8]. In this paper a clarification is searched for.…”

Section: Introductionmentioning

confidence: 92%

“…9. The change of the entropy during the retreat of the crystal front in the cause of the melting process according to Zachmann [2][3][4][5], shown by H. Baur [6]. -"~a corresponds to the melting entropy As z in (73); ct = degree of crystallinity However, according to the conception presented in the chapters III.A., B. and D. of this paper an equilibrium melting in c-direction in conformity with equation (73) and (74) is not possible because of the barrier mechanism, but only a lateral melting in a-and b-direction.…”

Section: Iiii1mentioning

confidence: 99%

“…6, 10 and 11), which had been fixed in various manners, H. G. Zachmann [2][3][4][5] evaluated statistically the conformational entropy which is related to the retreat of the crystal fronts during the melting process. According to these studies the conformational entropy ASLk should be a function of the degree of crystallinity a, as Baur [6] shows in figure 9 for different cases after Zachmann.…”

Section: Zlslk(a C*) = Asui(x2)mentioning

confidence: 99%

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Crystallization of low and high molecular materials

Kanig

1983

Colloid & Polymer Sci

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Konformation, übermolekulare Struktur und weitreichende Ordnung in nichtkristallinen und nichtstereospezifischen Polymeren Teil II. Die übermolekulare Struktur von Blockcopolymeren als Folge einer Unverträglichkeit der Sequenzen und der molekularen Konformation

Krömer

Hoffmann

Kämpf

1970

Ber Bunsenges Phys Chem

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Styrol/Butadien (SB)‐Blockcopolymere sind wegen der Unverträglichkeit der verschiedenartigen Sequenzen entmischt und deshalb mikroheterogen. Die entmischten Bezirke haben kolloidale Abmessungen und enthalten zu mindestens 90% nur eine Sequenzart. Um die Beziehungen zwischen der übermolekularen Struktur und dem Molekülbau zu klären, wurden systematische Untersuchungen an sorgfältig synthetisierten und charakterisierten SB‐Blockcopolymeren vorgenommen (siehe Teil I dieser Veröffentlichung). Die experimentellen Ergebnisse lassen sich theoretisch deuten und führen zu dem Schluß, daß in diesen Blockcopolymeren beide Arten von Sequenzen als statistische Knäuel mit ähnlichen Abmessungen wie in athermischen Lösungen vorliegen. Die übermolekulare Struktur wird in erster Linie durch die Raumerfüllung und gegenseitige Durchdringung solcher Knäuel, weniger durch die Grenzflächenenergie bestimmt. Mit Hilfe dieser Annahmen gelingt es, Abstand, Form und Größe der übermolekularen Aggregate vorauszuberechnen. Die Überlegungen lassen sich verallgemeinern und auch auf andere Blockcopolymere anwenden.

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Der Einfluß des Raumbedarfs der Kristallite auf die Entropie teilkristalliner Hochpolymerer

Cited by 33 publications

References 11 publications

Influence of Structural and Topological Constraints on the Crystallization and Melting Behavior of Polymers. 2. Poly(arylene ether ether ketone)

Influence of Structural and Topological Constraints on the Crystallization and Melting Behavior of Polymers. 2. Poly(arylene ether ether ketone)

Crystallization of low and high molecular materials

Konformation, übermolekulare Struktur und weitreichende Ordnung in nichtkristallinen und nichtstereospezifischen Polymeren Teil II. Die übermolekulare Struktur von Blockcopolymeren als Folge einer Unverträglichkeit der Sequenzen und der molekularen Konformation

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