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

Bogdanov, B.; Michailov, M.; Uzov, Chr.; Gavrailova, G.

doi:10.1002/macp.1994.021950628

Cited by 9 publications

(3 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, when the quenched samples are heated to 90 °C, the usual trigonal crystal modification, stable at room temperature, reappeared. 16 PEG-U-IC was investigated using X-ray diffraction previously by Suehiro et al It was suggested that all the reflections in the PEG-U-IC diffractogram can be indexed with a large tetragonal unit cell with unit cell dimension of a ) b ) 9.3 Å and c ) 19.51 Å. However, to date there is no report on the structural determination of PEG-U-IC single crystals.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Structure, Conformation, and Motions of Poly(ethylene oxide) and Poly(ethylene glycol) in Their Urea Inclusion Compounds

1996

View full text Add to dashboard Cite

X-ray diffraction and FTIR and 13 C NMR spectroscopies have been utilized to observe the inclusion compounds (ICs) formed by poly(ethylene oxide) (PEO) and low molecular weight poly(ethylene glycol) (PEG) oligomer with urea (U). We have confirmed that PEO-U-IC formed from solution has a trigonal crystal structure, while recrystallization from the melt produces a hexagonal PEO-U-IC. PEG-U-IC apparently adopts a crystal structure different from the trigonal and hexagonal forms of PEO-U-IC, and single crystals of PEG-U-IC are currently under investigation by X-ray diffraction. The conformations of PEO and PEG chains in their U-ICs appear similar to the TGT bulk crystalline conformation, while the all-trans conformer does not appear to be consistent with either the FTIR or the 13 C NMR observations. For solution-formed PEO-U-IC in the trigonal crystal structure, where one-third of the urea molecules are hydrogen-bonded to the PEO chains and reside in the channels, the mobility of the included PEO chains is similar to that of the bulk crystalline PEO. This is quite different from the usual observations made on hexagonal polymer-U-ICs, where spin-lattice relaxation times observed for the carbon atoms of the included polymers are much reduced (often more than 1 order of magnitude) from those observed for the same polymer in their bulk crystals. It is proposed that the direct involvement of the urea molecules in the trigonal channels of PEO-U-IC with the included PEO chains is the source of their reduced mobility.

show abstract

Section: Resultsmentioning

confidence: 99%

“…It has been shown that heating the trigonal crystal form to 150 °C and then quenching to 0 °C yields a crystal form different from the usual trigonal or hexagonal crystal structure. However, when the quenched samples are heated to 90 °C, the usual trigonal crystal modification, stable at room temperature, reappeared …”

Section: Resultsmentioning

confidence: 99%

Structure, Conformation, and Motions of Poly(ethylene oxide) and Poly(ethylene glycol) in Their Urea Inclusion Compounds

1996

View full text Add to dashboard Cite

show abstract

“…[12,13] By virtue of inter-species hydrogen bonding between the constituent polar molecules, the melting temperatures of the α crystals in the intermediate PEO/urea blend compositions were found to be considerably higher than those of the neat constituents. [14,15] Upon lowering temperature, there appeared another compound called β crystal in the PEO-rich region that melts in the vicinity of ~100 o C, i.e., intermediate between those of neat PEO crystal (i.e., 65 o C) and of the α crystal (i.e., 144 o C). [16][17][18] The β crystal was characterized as a metastable crystal that transformed reversibly to the stable α crystal upon heating and cooling.…”

Section: Introductionmentioning

confidence: 99%

Role of molecular complexation in solid-liquid phase diagram of poly-ethylene oxide/urea mixture

Kyu

2017

Polymer

View full text Add to dashboard Cite

Thermodynamic phase diagram of polyethylene oxide (PEO)/urea blend has been investigated with emphasis on the formation of induced crystals driven by molecular complexation. Of particular interest is that the complexed α crystal is more stable than those of neat constituents. The experimental solid-liquid phase diagram of PEO/urea blends has been analyzed in the context of the combined Flory-Huggins free energy for liquid-liquid demixing and phase field free energy of crystal solidification. The self-consistently calculated coexistence lines of the PEO/urea mixture exhibit an azeotrope type, accompanied by eutectoid reactions in the submerged regions, wherein the complexed α crystal decomposes into two coexistence crystalline phases. These coexistence crystalline phases were further analyzed by means of polarized optical microscopy, Fourier transform infrared spectroscopy, and wide-angle x-ray diffraction. A possible phase diagram of the complexed PEO/urea is constructed and discussed.

show abstract

Clathrates

Tarallo

2013

Encyclopedia of Polymer Science and Technology

View full text Add to dashboard Cite

Polymer clathrates are a fascinating class of crystalline host–guest compounds in which at least one component consists of a polymer species. In these compounds, the main component acts as the host, forming a cage‐like structure around the molecules of the guest. Polymer host–guest compounds can be distinguished in “polymer clathrates,” “crystalline polymer‐inclusion complexes,” “crystalline‐polymer molecular complex,” or “polymer intercalates.” Polymer clathrates are crystalline solids in which low molecular mass guest species are hosted inside cages or cavities of molecular size, generated by polymer chains. Crystalline polymer‐inclusion complexes are crystals comprising a polymer guest within a low molecular mass host whereas crystalline‐polymer molecular complexes are the crystalline molecular complex between different polymers. Finally, polymer intercalates are sandwich‐type inclusion compounds in which the guest molecules are entrapped in between layers of closely packed polymer chains. In the present article, the crystal structure and the main features of the most studied systems of each class, together with those of the nanoporous polymer crystals (ie, a polymer crystal presenting empty volume elements that can host low molar mass guest species) that can be obtained by removing the low molar mass guest species from some polymer host–guest compounds, are discussed. A review of the most promising applications in material science and technology of this class of host–guest compounds is also presented.

show abstract

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

Cited by 9 publications

References 7 publications

Structure, Conformation, and Motions of Poly(ethylene oxide) and Poly(ethylene glycol) in Their Urea Inclusion Compounds

Structure, Conformation, and Motions of Poly(ethylene oxide) and Poly(ethylene glycol) in Their Urea Inclusion Compounds

Role of molecular complexation in solid-liquid phase diagram of poly-ethylene oxide/urea mixture

Clathrates

Contact Info

Product

Resources

About