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Thermal properties of liquid crystalline aromatic random copolyesters containing two different mesogenic modifications within a polymer backbone
Author(s) -
Yoo Young Deuk,
Kim Sung Chul
Publication year - 1988
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1988.070350507
Subject(s) - mesogen , liquid crystal , mesophase , copolymer , materials science , differential scanning calorimetry , polymer chemistry , phase (matter) , crystallography , polymer , eutectic system , polarized light microscopy , organic chemistry , liquid crystalline , chemistry , microstructure , composite material , thermodynamics , optics , physics , optoelectronics
Two types of semiflexible mesogenic random copolyesters which contained both nematic and smectic type repeating units within the main chain were prepared and the thermal properties as well as the mesomorphic structures were characterized by differential scanning calorimetry and by polarizing microscope. The first type of copolymer (copolymer I) contained two repeating units which differed in the rigid mesogenic groups and the second (copolymer II) contained repeating units which differed in the length of flexible segment. Copolymerization disrupted the structural regularity of the crystal, lowered the crystal–mesophase transition temperature, and destabilized the molecular order of the smectic phase. These effects were more pronounced for copolymer II. However, the isotropization temperature was changed only slightly with the incorporation of the other mesogenic component. The crystal melting temperatures of both copolymers exhibited a eutectic behavior. A smectic to nematic transition, which was not observed for the homopolymers, occurred in the range of 0.4‐0.6 mole fractions of the smectic units for copolymer I and 0.5–0.85 for copolymer II. The molecular order of the nematic phase was slightly increased as the smectic units were incorporated, while those of the smectic phase became more disordered upon addition of the nematic units.