Synthesis and properties of liquid‐crystalline side‐chain polymers containing β‐diketonato transition metal complexes

Abstract

AbstractPolymers (5‐7) containing β‐diketonato metal complexes of Cu2+, Ni2+ and Co3+ were synthesized from new thermotropic liquid‐crystalline poly(acrylate ester)s (4) with a mesogenic bidentate β‐diketone in the side chain, and the liquid‐crystalline properties were examined by differential scanning calorimetry (DSC), X‐ray diffraction and polarizing microscopy. The mesophase of 4 is an enantiotropic smectic A phase showing a batônnet and focal conic fan texture in polarizing microscopy. Polymers 5a‐c containing a bis(β‐diketonato) copper(II) complex also exhibit an enantiotropic smectic A phase, and polymer 5d prepared from the vinyl monomer 8 shows a nematic phase. Concerning the complexes of polymers 6 and 7 with nickel(II) and cobalt(III), only 6a and 7a containing a small amount of metal‐chelating β‐diketonate units exhibit liquid‐crystalline behavior like the parent polymer 4. It was found that the fourcoordinated square planar bis(β‐diketonate)copper(II) acts as the mesogen; both nickel(II) and cobalt(III) complexes do not work as mesogens and rather hinder the liquid crystallinity of 4. The electron spin resonance (ESR) spectra of 5a and 5b change markedly along with the transition from the smectic A phase to the isotropic one. The broadening and simplification of the spectra for the isotropic phase indicates increased interaction between neighboring bis(β‐diketonato)copper(II) complexes and substantial electron spin‐spin interaction. The ESR spectra of 5c and 5d also imply this increased interaction between neighbouring complexes and spin‐spin interaction regardless of the phase transition.