Scanning electron microscopy analysis of the structure of thermotropic LC copolymers containing 2,7‐dioxynaphthalene or vanillate units

The morphological structure of the fibers and rods of two series of thermotropic liquid‐crystalline copolymers made of 2,7‐naphthalenediol/terephthalic acid/4‐hydroxybenzoic acid(B)/poly(ethylene 2,6‐naphthalene dicarboxylate) and vanillic acid/B/poly(ethylene terephthalate), was systematically analyzed by using a high‐resolution scanning electron microscopy (SEM) fractographic method. Based largely on the SEM micrographs and visual appearance of the fracture surfaces, the fibers and rods were found to consist mainly of highly oriented needle‐like fibrils or lamellae, at which some finely split connections appear. The uniformity of the fibrils is somewhat dependent on the copolymer composition. The macrofibrils with diameters in the range of 10–50 μm and the microfibrils with diameters in the range of 50–90 nm have been observed. No separate phase is obvious in the fibers containing no more than 70 mol‐% of the B unit which has been confirmed by differential scanning calorimetry, but in the rods containing 75 mol‐% of the B unit a few less‐deformed phases related to B‐rich phase were occasionally observed.