New thermotropic liquid‐crystalline polyesters with a metalchelated 1,3‐diphenyl‐1,3‐propanedione segment

New thermotropic liquid‐crystalline polyesters (2–4) containing a mesogenic β‐diketone segment, which can coordinate to a metal ion as bidentate ligand, were synthesized by polycondensation of a mixture of 1,6‐hexanediol (x mol), 1,3‐bis(p‐hydroxyphenyl)‐1,3‐propanedione (y mol), and 4,4′‐hexamethylenedioxydibenzoyl chloride (x + y mol). Homopolyester 1, prepared from 1,6‐hexanediol and 4,4′‐hexamethylenedioxydibenzoyl chloride, and copolyesters 2 and 3 (x/y = 0,8/0,2 and 0,5/0,5, respectively) show a nematic phase, whereas homopolyester 4, prepared from 1,3‐bis(p‐hydroxyphenyl)‐1,3‐propanedione and 4,4′‐hexamethylenedioxydibenzoyl chloride, exhibits a smectic phase. The wide‐angle X‐ray diffraction patterns from the melt‐drawn fibers prepared at mesophase temperatures suggested no orientation for 1, a monoaxial orientation and a crystalline state for 2, a monoaxial orientation and a frozen‐in nematic phase for 3, and a biaxial orientation and a frozen‐in smectic A phase for 4. Introduction of a transition metal (CuCl2 or NiCl2) into copolyesters 2 and 3 gave the corresponding metal‐chelated thermotropic liquid‐crystalline polyesters (5a–c, 6a–c, and 7a–c). Formation of a metal complex among polymer chains by introduction of a metal ion also resulted in better monoaxial orientation according to X‐ray diffraction patterns. The ESR spectra of fibers of copper‐containing polyesters (5a–c and 6a–c) indicated that the plane of the square planar copper complex in the polymers is oriented parallel to the fiber axis.