Side-chain functionalized liquid-crystalline polymers and blends. IX. Phase behavior and structure of comb-shaped liquid-crystalline ionomers containing calcium ions

Liquid-crystalline (LC) ionomers containing 2-15 mol % calcium ions were synthesized by the exchange reaction between the nematic LC copolymer, bearing oxycyanobiphenyl mesogenic groups, and the carboxyl groups of acrylic acid, with calcium acetate. The incorporation of 2-3 mol % Ca ions in the LC copolymer leads to some rise in the clearing point and glass-transition temperature. A further increase in the concentration of metal ions (>5 mol %) is accompanied by induction of the smectic A phase where clearing point and glass-transition temperatures keep constant values. Phase behavior of the LC ionomers may be understood on the basis of a structural model that considers the dual role of calcium ions in a polymer matrix. Metal ions act as points of noncovalent electrostatic binding of the polymer chains and are capable of forming larger ionic associates (multiplets). The comparison of the phase behavior of sodium and calcium containing LC ionomers shows that the formation of ionic links may lead to the growth of structure defects suppressing a positive influence of charged groups on the mesophase clearing temperature. The orientation behavior of the LC ionomers in the magnetic field was studied. It was shown that the incorporation of calcium ions (3 mol %) in the LC copolymer matrix leads to the growth of orientation order parameter S of the nematic phase. (C) 2001 John Wiley & Sons, Inc.