ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The structural and thermal behavior of liquid-crystalline polyesters at hydrostatic pressure was investigated by using a high-pressure DTA and a wide-angle X-ray scattering apparatus equipped with a high-pressure sample vessel. The thermotropic polyesters (two homopolymers and the corresponding copolymer) are based upon 4,4′-biphenyldiol as the mesogen and aliphatic dibasic acids containing 7 and 8 methylene groups as flexible spacer, which are labeled as PB-7, PB-8, and PB-7,8 (30/70 mol-%), respectively. The phase diagrams of the PB-7, PB-8 and PB-7,8 samples were constructed for pressures up to 300 MPa. At room temperature both the PB-7 and the PB-8 crystals are compressed hydrostatically in the molecular chain and lateral packing directions. The d spacing of the low-angle reflection of the PB-8 crystal, corresponding to the layer spacing, decreases by about 2,6 ± 0,2 Å at the crystal (K)-smectic H(SH) transition under all pressures, while the crystal reflections of PB-7 disappear at the K-nematic (N) transition. The d spacings of the wide-angle reflections of both crystals, corresponding to the lateral packing in the crystals, expand gradually with increasing temperature up to the K-mesophase transition. The increase in lateral spacing of the PB-8 crystal at the K-SH transition changes slightly from ca. 0,29 Å at 0,1 MPa to 0,22 Å at 300 MPa. It is concluded that the transition mechanisms of the K-SH transition of PB-8 and the K-N transition of PB-7 are maintained at pressures up to 300 MPa.
Additional Material:
13 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1993.021941116
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