Die kristallisation eines geschmolzenen molekülkomplexes aus hochmolekularem polyoxyethylen und harnstoff

Bogdanov, B. S.; Michailov, Marin; Uzov, Chr.; Gavrailova, G.

doi:10.1002/apmc.1992.051950113

Cited by 6 publications

(2 citation statements)

References 8 publications

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“…In contrast, the β complex has a 12:8 EO:urea stoichiometry and it is much more difficult to prepare because of its incongruent melting at 90 °C that yields a PEO‐rich liquid and crystals of the α complex 12. It has most often been obtained by melt‐quenching the α complex, but this process leads to a metastable mixture of β complex and urea 4, 5. We recently showed that the pure β complex prepared by electrospinning is thermodynamically stable and suggested an intercalated structure with layers of PEO and urea 16…”

Section: Resultsmentioning

confidence: 99%

“…These complexes sometimes present an incongruent fusion, in which case they typically melt to yield a polymer‐rich peritectic liquid and crystals of the pure small molecule. This creates a challenge for the preparation of pure complex samples when using most common synthesis methods such as cocrystallization from concentrated solutions, melt‐cooling, or solvent casting 2–8. Indeed, the system has to pass through a region of the phase diagram where crystallization of the small molecule is thermodynamically favored and, as a consequence, samples often consist in mixtures of the complex with crystals of the small molecule and residual polymer.…”

Section: Introductionmentioning

confidence: 99%

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Polymer Complexes with Congruent and Incongruent Fusion by Spin Coating

Richard‐Lacroix

Pellerin

2011

Macromolecular Symposia

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We demonstrate that spin coating is an efficient method for preparing pure complexes between polymers and small molecules. Samples of the a and b complexes between poly(ethylene oxide) and urea were prepared as proof-of-concept examples since they show congruent and incongruent fusion, respectively. Infrared spectroscopy showed that pure complex of both types could be obtained by spin coating from solutions in various solvents. The ultrafast solvent evaporation appears to be the key factor in preventing the crystallization of the small molecule. These results suggest that this simple method could be generally applicable to a wide range of systems.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polymer Complexes with Congruent and Incongruent Fusion by Spin Coating

Richard‐Lacroix

Pellerin

2011

Macromolecular Symposia

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Phase transformation on heating of undercooled melt of poly(ethylene oxide)‐urea molecular complex

Bogdanov

Michailov

Uzov

et al. 1994

Macro Chemistry & Physics

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X-ray and calorimetric investigations of the structure and transformations on heating of quenched (undercooled) samples of poly(ethy1ene oxide)-urea molecular complexes are discussed. It was established that at room temperature the undercooled melt of the molecular complex contains free urea in a tetragonal crystal modification and a high-temperature poly(ethy1ene oxide)-urea molecular complex whose crystal modification does not coincide with the known hexagonal crystal structure of the molecular complex obtained from solution or by slow cooling from the melt. It was shown that on heating this molecular complex to a temperature between 87,5 and 90 "C, the hexagonal crystal modification, stable at room temperature, is obtained.

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Characterization of the stable and metastable poly(ethylene oxide)–urea complexes in electrospun fibers

Liu

Antaya

Pellerin

2008

J Polym Sci B Polym Phys

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Solution electrospinning was used for the first time to prepare nanofibers of the stable (α) and metastable (β) complexes between poly(ethylene oxide) (PEO) and urea. Both types of fibers were highly crystalline and presented a large level of molecular orientation. Detailed characterization of the ill‐studied β complex was performed using wide angle X‐ray diffraction (WAXD), infrared spectroscopy, and differential scanning calorimetry (DSC). Results reveal that it possesses a 3:2 PEO:urea stoichiometry and suggest that it belongs to the orthorhombic system with a = 1.907 nm, b = 0.862 nm, and c = 0.773 nm. The PEO chains are oriented along the fiber axis and present a conformation significantly affected by strong hydrogen bonding with urea when compared with the pure polymer and the stable complex. A layered structure model is suggested for the metastable complex, in which the urea molecules would be arranged into a ribbon‐like structure intercalated between two PEO layers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1903–1913, 2008

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Die kristallisation eines geschmolzenen molekülkomplexes aus hochmolekularem polyoxyethylen und harnstoff

Cited by 6 publications

References 8 publications

Polymer Complexes with Congruent and Incongruent Fusion by Spin Coating

Polymer Complexes with Congruent and Incongruent Fusion by Spin Coating

Phase transformation on heating of undercooled melt of poly(ethylene oxide)‐urea molecular complex

Characterization of the stable and metastable poly(ethylene oxide)–urea complexes in electrospun fibers

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