Macromolecules, Vol.37, No.15, 5490-5494, 2004
New chiral nematic ionomers containing metal ions
The series of new chiral nematic ionomers containing 0.7-9.0 mol % ions of alkali metals Na and transition metals Co(II) were synthesized by the exchange reaction between chiral nematic N* functionalized liquid crystalline (LC) copolymers bearing the phenylbenzoate mesogenic fragment, optically active moiety (derivatives of cholesterol), and carboxylic groups with acetate of cobalt and sodium. For ionomers containing 0.7-9 mol % sodium ions the melting point is independent of temperature. At the same time, the incorporation of cobalt ions in the polymer matrix leads to decreasing of clearing temperature and destruction of the mesophase at the concentration of transition metal higher than 6 mol %. All ionomers produce the chiral nematic phase, which is characterized by selective light reflection the spectral range 500-2000 nm. The introduction of even small amounts of metal ions to functionalized LC copolymer prevents untwisting of pitch of the helix with decreasing the temperature. This tendency is related to a limited translational mobility of side groups in the LC copolymer, which produce helical structure, due to the physical network as formed by charged groups.