LC Ionomers with Phosphonate Groups and Their Multilayer Build-Up

Abstract

This paper describes the synthesis of new liquid-crystalline (LC) ionomers (semiflexible LC main-chain polymers with ionic groups as side groups) by polycondensation of substituted malonates with mesogenic diols. Phosphonic acids were used as negative groups, and phosphonium and ammonium ions as positive groups. The presence of these ionic groups leads to gelation (physical crosslinking) of the polymers, which display a rubbery consistency. As expected from the reference polymers without an ionic group, all polymers show smectic phases. These phases are destabilized by bulky side groups (e. g., phosphonium ions or phosphonic acid esters). They are, however, stabilized by phosphonic acid groups and the corresponding salts. Together with X-ray measurements this supports the assumption that different smectic sublayers are formed for the mesogens and the ionic groups. Dielectric relaxation measurements show four different relaxation processes for these polymers. They are, with rising temperature, the χ- and the β-relaxation (local relaxations, active below Tg) and an α- and a δ-relaxation above Tg. The α-relaxation corresponds to the dynamic glass process and the δ-relaxation is due to a reorientation of the mesogenic groups around their short axis. Despite the fact that these LC ionomers have only one ionic group per repeating unit (one group per 3.3 nm), they could be successfully used for a multilayer built-up by electrostatic deposition. The resulting multilayers are rather hydrophobic, if the LC ionomer is the outermost layer.