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.