Liquid-crystalline copolyester films

Quantitative Small-Angle Light Scattering of Liquid Crystalline Copolyester Films... 

Various process steps were used to determine their Influence on the morphological nature of liquid crystalline copolyester films. Compression molding was used to form quiescent films, while extenslonal deformation above and below the onset of fluidity, as well as shear deformation above the onset of fluidity was used to make non-quies-cent films. It Is a basic result that molecular orientation can only be achieved when the deformation is done while the polymer is In a liquid crystalline melt state. Experimental details are given In the subsection Materials and Processing, while an interpretation is offered in the discussion in the subsection Morphological and Process Consideration. ... 

Chung Tai-Shrmg, Cheng Si-Xue. (2000). Effect of Catalysts on Thin-Film Polymerization of Thermotropic Liquid Crystalline Copolyester. J. Polym. Sci. A, 38(8), 1257-1269. 

Teoh, M. M., Liu, S. L. Chung, T. S. (2005). Effect of Pyridazine Structure on Thin-Film Polymerization and Phase Behavior of Thermotropic Liquid Crystalline Copolyesters. J. 

Materials and Processing. Copolyesters of poly(ethylene terephtha-late) (PET) and para-oxybenzoic acid (FOB) were supplied by the Tennessee Eastman Corporation. Past work Indicates the copolyesters form thermotropic liquid crystalline phases at compositions containing more than 30 mole% POB (26,27,28). The composition of the copolyester studied here contains 60 mole% POB. Quiescent liquid crystalline films were made by compression molding the copolyester at 210, 230, 255, and 285 C, and followed by a quench Into Ice water, ambient air, or cooled In the press with the power off. Film thicknesses ranged between 0.05-0.15 mm. Another sa(q>le of the 40/60 PET/POB copolyester was melted at 270 °C In a Mettler hot stage, manually sheared between glass slides, and then ambient air cooled. 

When the copolyester is heated up or cooled down in the liquid crystalline state fluctuations in the scattering intensity can be observed. Fig. 56 shows the intensity obtained by a position sensitive linear detector and integrated from 29 = 12° 26 = 30° as a function of time. Obviously, the time scale of the fluctuations lies in the region of minutes. Measurements at different azimutal angles reveal that the fluctuations are caused by changes in the orientation of the chains. The area of the film from which the scattering arises is about 2 mm x 2 mm. 

To date, reports of investigations on the gas transport properties of main chain liquid crystalline polymers appear to have been limited to the work conducted in our laboratory. Chiou and Paul (4.) have briefly described the transport parameters of an extruded film of an LCP having a similar structure to the commercial product Vectra. This copolyester belongs to the family of napthylene thermotropic polymers (NTP s) commercialized by Hoechst-Celanese Corp. whose synthesis and properties have been described previously (iLS.). Transient permeation experiments were conducted with a series of gases. The effective... 

Transient permeation experiments were conducted on the copolyester films using a series of gases in the same manner described previously. In Table 5, the transport coefficients of the liquid crystalline films can be compared with amorphous and semi-crystalline PET(22). 

The development of ordered bands perpendicular to the shear direction in the oriented film of both copolyester compositions is an optical effect observed with liquid-crystalline behaving polymers under mechanical stress conditions and appears to relate to the electro-optical effects observed in nematic liquid crystals. The non-uniform distribution of shear bands in the oriented film of the 20/80 copolyester composition is due to the inhomogeneity of its mesophase which is composed of rich PET and PHBA areas because no shear bands are observed readily in oriented film which is prepared below 310-320 °C, that is when the PHBA domains are not fused. ... 

This chapter describes the recent application of TEM to the study of thin films of several thermotropic random copolyesters. The interpretation of the micrographs obtained requires concepts in addition to those previously established for crystalline and amorphous materials, because liquid... 

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