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Crystallization behavior of polyethers containing odd numbers of methylene spacers from the isotropic and liquid crystalline states
Author(s) -
Yandrasits Michael A.,
Chen Jianhua,
Arnold Fred E.,
Cheng Stephen Z. D.,
Percec Virgil
Publication year - 1994
Publication title -
polymers for advanced technologies
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.61
H-Index - 90
eISSN - 1099-1581
pISSN - 1042-7147
DOI - 10.1002/pat.1994.220051203
Subject(s) - mesophase , materials science , differential scanning calorimetry , liquid crystal , crystallography , crystallization , thermotropic crystal , amorphous solid , polarized light microscopy , glass transition , methylene , chemical engineering , organic chemistry , composite material , thermodynamics , polymer , optics , chemistry , liquid crystalline , physics , optoelectronics , engineering
A series of thermotropic polyethers synthesized from 1‐(4‐hydroxyphenyl) ‐ 2 ‐ (2 ‐ methyl ‐ 4 ‐ hydroxyphenyl) ‐ ethane and α,ω‐dibromo‐n‐alkanes with odd numbers of methylene units (MBPE‐n = odd) shows monotropic mesophase behavior. In isothermal differential scanning calorimetry (DSC) experiments, two—sometimes even three—exothermic transition processes can be observed when the crystallization temperature is below the mesophase transition temperature, while only one exothermic process is present above the mesophase transition temperature. The melting behavior of the crystals grown from the mesophase and from the isotropic melt states is different. The crystals grown from the mesophase state exhibit a larger overall heat of transition and a higher transition temperature compared with those grown from the isotropic melt. This may be attributed to the molecular interfacial connections between the crystal and amorphous regions when MBPEs crystallize from the mesophase state. The difference in morphology between the crystals grown from the different states has also been studied with polarized light microscopy (PLM) and transmission electronic microscopy (TEM). The structures of the crystals grown from the different states are, however, the same, as evidenced through wide‐angle X‐ray diffraction (WAXD) measurements. From the banded morphology of MBPE samples observed from PLM, the defect textures observed through TEM and the results of WAXD experiments, this mesophase can be identified as a nematic liquid crystal state.