Synthesis and properties of novel chiral side-chain liquid crystalline polysiloxanes containing different chiral pendant groups

摘要

Two novel chiral liquid crystalline monomers, and a series of their corresponding chiral side-chain polymers (P_1-P_7) based on poly(methylhydrogeno)siloxane have been prepared. The chemical structures and liquid crystalline properties of the synthesized monomers and polymers have been investigated using various experimental techniques. Thermal analysis shows that all polymers have wide mesophase temperature ranges with a high thermal stability. With the increase of M_2 molar ratio in the polymer systems, the isotropic phase transition and glass transition temperatures of all polymers increase, and the temperature ranges of N~* phase and mesophase become broad. The effect of cholesteryl mesogens on mesophase behaviors, optical properties, and molecular arrangement of LC polysiloxanes and their advanced applications have also been discussed. For homopolymer P_1, it shows a single S_A phase. With increasing the content of M-2 in the polymer systems, P_2 and P_3 reveal a S_A-N~* phase transition when they are heated, and P4-P7 reveal a N~* phase. For N~* phase polymers P_4-P_7, the reflection wavelengths exhibit blue shift, suggesting that the pitch decreases with a decrease in the amount of the smectic domains induced by the M_1. The reflection wavelengths of P_4-P_7 are almost across the entire visible region when they are heated, which offer stremendous potential for various optical applications. For P_2 and P_3, the reflection wavelengths show a very steep change around the temperature of the S_A-N~* phase transition, which can be used as thermally sensitive liquid crystal devices requiring fast response, such as sensors, and thermally induced tuning.