Textures of thermotropic liquid-crystalline copolymers containing either 2,7-, 1,5- or 1,4-naphthalenediol or vanillic acid units

The melts of the thermotropic liquid-crystalline copolymers prepared from 2,7-, 1,5- or 1,4-naphthalenediol (N)/terephthalic acid/4-hydroxybenzoic acid/poly(ethylene 2,6-naphthalene dicarboxylate) or vanillic acid (V)/4-hydroxybenzoic acid/poly(ethylene terephthalate) and other five types of 4-hydroxybenzoic acid/poly(ethylene terephthalate)/comonomer copolymers are turbid and exhibit a thready texture on the basis of visual observation. Strong shear and stir opalescences in the copolymer melts are also observed. The polarized light micrographs of the melts show a marble or threaded schlieren texture which is a typical optical texture of the nematic mesophase. The polarizing microscopy observation indicates that the vanillate unit-containing copolymer films obtained by drawing the melts are highly oriented and fibrillated, Elliptical light scattering patterns are obtained for the sheared films of the copolymers, suggesting the existence of a preferred orientation of the copolymer chains. The X-ray fiber diagrams of the extrudates from the 2,7-N and 1,5-N, and V units-containing copolymers, show broad halos centered at 0.436-0.444 nm and diffraction spots centered at 1.2-1.5 nm along the equator that are reminiscent of amorphous polymers with a ''frozen'' nematic phase, indicative of chain orientation. Additionally, the X-ray fiber diagram of the V unit-copolymer film shows strong meridional reflections at spacings 0.208 and 0.328 nm, representing the molecular repeat spacing of the copolymer chains. The X-ray fiber diagram of 1,4-N unit-containing copolymer rods exhibits two diffuse annular rings, the outer at the d-spacing 0.438 nm and the inner at 1.3 nm, indicating no definite order or amorphous structure.