Side­chain liquid crystal polymers derived from oxetane monomers containing 2­ or 3­fluorophenyl moieties in the core of the mesogen

Abstract

Two series of side-chain liquid crystalline polymers were prepared by cationic ring-opening of oxetane substituted mesogens. Each of the terminally appended side chain polymers prepared had a flexible spacer length of six methylene units separating a mesogenic aromatic core from the polymer backbone. The core unit was designed to incorporate either a 2-fluoro- or a 3-fluoro-phenyl unit possessing either an (R)-(−)-1-methylheptyl, (S)-(+)-2-methylbutyl or a 1-propylbutyl terminal chain. The materials produced in this study were compared with the previously reported unsubstituted parent materials in order to assess the affect of having a lateral fluoro substituent in the core. Low melting points, smectic C/C* and smectic A/A* phases were exhibited by most of the monomers. The behaviour of the 3-fluorophenyl monomers was found to be similar to their unfluorinated parents, whereas the 2-fluoro analogues were shown to have significantly lower transition temperatures. All of the polymers exhibited smectic C/C* and smectic A/A* phases over wide temperature ranges and had relatively low Tg values. Some of the polymers were found to exhibit exceptionally large temperature ranges for the smectic C/C* phase, e.g. from 0.8 °C to 190 °C.